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Royal Australian Chemical InstituteNSW BranchQuiz a Chemist |
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What is Phenolphthalein clear in?
What are some acid base indicators?
I have a series of questions on distillation and purification technique. Could you please help?
What is an independent and dependent variable in an experiment?
What method of analysis would you recommend to test the concentration of Fulvic Acid?
Please explain the concept and ideas in simple English, on Atomic Absorption Spectroscopy.
How is silver made into its pure form?
Is Le Chatelier's Principle a generalisation of a scientific truth?
What is the specific gravity of an 18% Hydrochloric Acid Solution?
Analytical Chemistry - Answers
What is Phenolphthalein clear in?
(April)
Phenolphthalein is clear at all pHs. It is however coloured (pink) above pH 7, and colourless below that pH.
(Note the difference between "clear" and "colourless". A liquid can be clear and colourless, like water. A liquid can be white and opaque, like milk, or it can be coloured and opaque, like strawberry-flavoured milk. Lasttly, it can be clear but coloured, like orange cordial.)
What are some acid base indicators?
(April)
Litmus, thymol blue, bromocresol purple, methyl red etc.
I have read an article on the preparation of medicines. I do have a science degree, but I cannot remember a number of things and can not find it in my outdated textbooks:
1. How does one extract with ether and chloroform?
2. What is a vacuo? Is it the same as a fume cupboard?
3. How does one ""reflux"" and what is a reflux condenser?
4. What is an addition funnel? Is it the same as a thistle funnel?
5. What does it mean to ""heat to reflux""?
6. How does one ""take up the residue in the minimum amount of water and decolourize with carbon""?
7. Is 20* the same as 20 degrees Celsius? I read the article on the internet.
8. What does it mean: ""the product comes over at 110*""?
9. Please define psi.
10. How does one ""recrystallize from ethanol to purify""?
11. Is 0i the same as 0 degrees Celsius?
(Owen )
1. How does one extract with ether and chloroform?
Answer: Usually this is referring to a 2 phase system, and extraction occurs using a separatory funnel. That is, the compound to be extracted is soluble in either ether or chloroform, and so an aqueous mixture is combined with ether or chloroform to extract the pure compound. When mixed, the compound goes into the organic phase, which is immiscible with the aqueous, and so the 2 phases can be separated.
2. What is a vacuo? Is it the same as a fume cupboard?
Answer: This is an unfamiliar term, and may be specific to the method you are reading, but vacuo is more likely to refer to a technique involving a vacuum or removal of the atmosphere, such as a vacuum oven, or maybe a rotary evaporator.
3. How does one "reflux" and what is a reflux condenser?
Answer: Product from a reflux is a liquid which has been partially condensed after being vaporised. So the equipment used is akin to a distillation rig, where a vertical, jacketed fractionating column (reflux condenser) sits above the flask. At right angles and on a downward slope to the fractionating column may be a standard condenser, a glass tube with an outer jacket flushing with cold water to condense the vapour that leaves the fractionating column (at a controlled temperature, in order to discretely separate that product from all else in the flask). At the end of this condenser is a clean vessel in which to collect the condensed product. So to reflux, the solvent is heated to boiling point, the vapour condenses and drops back into the system (reflux). Otherwise it is boiled over to condense and be collected separately (distill).
4. What is an addition funnel? Is it the same as a thistle funnel?
Answer: An addition funnel is a standard funnel, used for adding solids or liquids into a flask (or other vessel). A thistle funnel is similar to an addition funnel, but has a specific use. It is like an upside down addition funnel that is normally used in the process of generating a gas.
5. What does it mean to "heat to reflux"?
Answer: See the answer to question 3; if you are only refluxing, then all products in the flask are simply heated to vapour (boiling point), then recondense back into the original flask.
6. How does one "take up the residue in the minimum amount of water and decolourize with carbon"?
Answer: This is describing a purification step. That is, the residue is obviously soluble in water, so the method is to use the minimum amount of water so as to concentrate the residue, then pass it over activated charcoal (carbon), using a Buchner funnel and filter paper (size chosen carefully).
7. Is 20* the same as 20 degrees Celsius? I read the article on the internet.
Answer: Unfortunately the symbol you are asking about appeared on our system as an asterisk (*), so we can only assume the symbol was a small "o", superscript, in which case it denotes degrees Celsius.
8. What does it mean: "the product comes over at 110*"?
Answer: Again, this is talking about the reflux procedure, where the product you are retrieving will be that fraction that distills (or boils) at 110 degrees Celsius.
9. Please define psi.
Answer: Pounds per square inch (a term for pressure)
10. How does one "recrystallize from ethanol to purify"?
Answer: This is another purification step. Dissolve the compound in hot ethanol, then hot filter the solution to remove the impurities. When the solution cools, the purified product should crystallize out.
11. Is 0i the same as 0 degrees Celsius?
Answer: Sorry, we can only see a lower case "i", so are not sure of the question, so we can only assume it is the same as question 7.
What is an independent and dependent variable in an experiment?
(Freda)
This terminology is usually used in graphing where the independent variable (eg time) is on the x-axis and the dependent variable is on the y-axis (eg: concentration of the product of the reaction). In terms of an operational definition: in an experiment where we want to know how some physical property changes with change in concentration, then we would make a series of solutions of different concentration and measure the physical property for each solution. The concentration is the independent variable (because we set it) and the physical property is the dependent variable.
In a mathematical sense for the function y = f(x), x is the independent variable and y is the dependent variable because the value of y is determined by substituting in a value of x.
I was wondering, how do the following
separation techniques work: a) Immiscible Solvents, b) Melting point determination,
c) Centrifugation, d) Simple distillation, e) Sublimation
(Melissa Eaton)
a) Immiscible solvents are those which do not mix with each other (eg: water and mercury), and therefore can be physically separated. The most common technique is to use a separatory funnel.
b) Melting Point Determination: Individual elements and compounds have unique melting points (ie: the temperature at which the compound passes from the solid to the liquid phase). Therefore with a mixture of compounds, by performing a melting point test, you will be able to determine how many compounds are present in the mix by observing their progressive melting points.
c) Centrifugation: This is the separation of substances by means of a centrifuge. A centrifuge is a machine whic employs centrifugal (or spinning) force to attain high rates of sedimentation or filtration in order to separate a solid from a liquid.
d) Simple Distillation: This technique is similar to that described in b), except with distillation you are working with the boiling points of the substances. So, we are looking at the liquid moving to the gas phase. Each gas phase is then condensed to give its respective liquid (purified), and so you have separated the mixture.
e) Sublimation: This process is the volatilisation of a solid substance into the vapour phase, without passing through the liquid phase. It is also a process of purification in which the vapour is condensed directly to a solid.
What method of analysis would you recommend to test the concentration of Fulvic Acid? We are using "Organic materials method of Walkley and Black"
(Federico Casillas)
Fulvic Acid is a carboxylic acid. Titration with NaOH will give the number of moles of the acid present. The theoretical number of moles is calculated from the mass used and the molar mass. The degree of purity can then be determined by percent purity. That is:
% Purity = (Experimental moles/Theoretical moles) x 100
Several titrations should be performed to give some idea of accuracy.
Please explain the concept and ideas in simple English of Atomic Absorption Spectroscopy (AAS).
(Derek Garrison)
The basis of AAS is the result of the electronic structure of the atom.
Electrons are able to absorb quanta (a given amount) of energy. When this
happens they are promoted to another energy level. Each wavelength of light
carries a different amount of energy, according to the Planck equation (E
= hc/wavelength), and as a result of the absorption, a dark line appears
in the spectrum. Since each element has a different set of electronic energy
levels, each has its own set of absorption lines. Quantification, determining
the amount, of an element can be achieved by looking at the amount of light
at a given wavelength which is absorbed. According to the Beel-Lambert Law,
the amount of light absorbed is proportional to the amount os a substance
present.
How is silver made into its pure form?
(Kristi-Lee Lannan)
Silver can be made by one of two ways.
a) Dissolve the impure silver in a strong acid solution followed by electrolysis
b) Smelting: the impure solid is melted and air is bubbled through the liquid causing the impurities to float to the surface where they can be skimmed off the top.
Is Le Chatelier's Principle a generalisation of a scientific truth?
(Michael Lum)
Le Chatelier's Principle is not a generalisation and can be defined as when a constraint such as heat or pressure is applied to a system in equilibrium, the equilibrium will tend to move in such a way as to neutralise the effect of the constraint. So, in a reaction such as:
N2O4 þ-----------¦ 2NO2
Increasing the total pressure will cause the equilibrium to move towards the formation of more N2O4, thereby decreasing the total number of molecules in the system.
How many calories per minute does a blue flame release? And how many calories per minute does a yellow flame release?
(Raymonf Serrano)
The colour of a flame is proportional to the energy being released. Therefore yellow is cooler than blue. Energy released is ~225kJ/mol of the gas. However, the energy released per minute will be dependent on the flow rate. So further information is required to be able to answer your question. Hopefully you have enough information now to do the calculation yourself.
What is the specific gravity of an 18% Hydrochloric Acid Solution?
(Kerry Crockett)
The answer to this is available in any standard chemistry reference book. We used the CRC Handbook of Chemistry and Physics. SG of 18% HCl at 20oC is 1.0898 kg/l.
In medicines and some shampoos you can come across terms like "contains 5% w/w". What does this mean?
(Paul Cox)
% w/w is a unit of measurement describing concentration. In full it stands for "weight for weight". So 5% w/w means that every 100g of the product contains 5g of the ingredient or component listed. Similar units also describing concentration are w/v (weight per volume) and v/v (volume per volume).
So far we have not received any questions on this topic.
So far we have not received any questions on this topic.
How do you know what shampoo or skincare products are right for each person?
What is the chemical equation for shampoo?
I need assistance with a school project on the chemistry of perfumes and fragances
Cosmetics - Answers
How do you know what shampoo or skincare products are right for each person?
(Bradley A. G. Hanna)
This question is one rightly answered by the medical experts. However the RACI response seeks to describe how shampoos and skin care products are prepared.
Depending upon their ingredients shampoos and skin care products are legally regarded as either cosmetics or as therapeutic goods. The latter contain an active ingredient(s), known to promote a beneficial therapeutic effect. Shampoos are solutions or emulsions, containing detergents to aid in the washing of hair. They are also likely to contain colourings and perfume. The most common medicated shampoos contain an active ingredient to aid in dandruff control.
Skin care products are oils, lotions and creams. Again these may be medicated or unmedicated, depending upon an individual's expectations and needs.
Creams and lotions are emulsions. Emulsions are an intimate mixture of very fine droplets of either oils or water, surrounded by a continuous phase of the other. The stability of the emulsion, ie to stop separation into water and oils, is maintained by means of surface active agents known as surfactants. Emulsions can be either “oil-in-water” or “water-in-oil”. Cold cream is an example of the former and a thinner moisturiser (usually) an example of the latter. A water-in-oil emulsion, when applied to the skin, is more likely to repel water. Emulsions are manufactured by heating water and oils and mixing. “Label Claim” ingredients, surfactants and perfumes and colourings are added, all with constant high speed and stirring and homogenising before cooling. The choice of ingredients and their concentrations dictate the effect of the emulsion on the skin.
What is the chemical equation for shampoo?
(Sarina)
As it happens, there is not a " chemical equation", but rather a formulation of various chemicals. If you read the labels on the back of any commercial shampoo bottle, all the chemicals mixed to produce that shampoo are listed. Of course, for trade practice purposes, the proportions of each component are not listed, nor the process used to mix them.
I am in an accelerated chemistry class. For this class, I have to do a project and explain the procedures and reason why I am doing this project. For my project, I have decided to make different scents and fragrances. I also have to list at least 5 different variables for this project. I have NO clue on what I am doing. Also, for this project I am going to have to find some complex chemicals. I have no idea where to find them! Please help! I am very desperate.
(Desperate Gina)
Dear Desperate Gina,
On the project of scents and fragrances, to kick start you, here are five variables to consider:
a) Extractions from natural materials
b) Synthesis of perfumes
c) Blending of individual compounds and fragrances for a particular perfume
d) Use of perfumes and fragrances in products (eg: scents in liquids, creams and aerosols as separate items)
e) Industrial applications such as toiletries and household fragrances
A more appropriate body of people to approach, however, would be the Cosmetic Toiletry and Fragrance Association of Australia
140 Arthur Street, North Sydney Phone: (02) 9927 7500
Good luck with your project.
From where can I get an Aromatic dictionary. Which book can be consulted for making fragrance compounds from aromatic chemical and essential oils?
(Muhammad Slaeem)
"Perfumery: Practice and Principles" by RT Calkin and SJ Jellinek, published by Wiley (1994).
So far we have not received any questions on this topic.
When sodium is added to a container of water, why does it go bang?
How do you make pure samples of sodium Na?
Dangerous Goods / Hazardous Substances - Answers
When sodium is added to a container of water, why does it go bang?
(William John Bailey)
The bang is from a small explosion, but it's not the sodium and water that are exploding. Together, these react to form hydrogen gas. When this hydrogen is ignited (usually by a spark from the sodium), it explodes. Don't try this one at home, folks!
How do you make pure samples of sodium Na?
(Krystle)
Sodium metal is made by electrolysis of sodium chloride (common salt).
Na(+) + electron -> Na metal
(Sian)
Teratogen is a chemical which produces malfunction, generally in the form of mutations or tumours.
How do you make all the different medicines?
Where can I get Skin Cancer cream?
What is the chemical structure for glucogen and insulin?
Is there anyone in Australia who may be able to manufacture or supply compounded T3?
How do I make tablets for medicine, what is the procedure?
What tablet is carbamazepine and what is it for and what does it have in it?
Drugs and Medicines - Answers
How do you make all the different medicines?
(Bradley A. G. Hanna)
This question requires a very detailed answer. Go to this link for details.
Where can I get Skin Cancer cream?
(Natasha Gorbunova)
Your question is unfortunately not one which any onf our members are able to answer. This is more a medical question, and we advise you speak with your doctor about it, or contact the Cancer Foundation. While the RACI has pharmaceutical chemists, none of them have expertise in this field.
What is the chemical structure for glucogen and insulin?
(Stacey)
Glucogen: This is a brand name, you probably mean GLYCOGEN: (C6H10O5)x. The molecule is built up of a large number of short chains with 12 or sometimes 18 alpha-glucose units joined by 1-4 links, the chains being cross-linked by alpha-1-6 glucoside links. The molecular weight is about 4 million g/mol!
Insulin: Insulin is built up of 2 polypeptide chains, "A" of 21 amino acids, and "B" of 30 amino acids, linked by 2 disulphide bridges.The molecular weight of insulin is 6500g/mol.
We have been in contact with the Wilsons Syndrome Foundation in Florida and are seeking to obtain compounded T3 here in Australia. Is there anyone in Australia who may be able to manufacture or supply this substance as described by Dr Wilson (website www.wilsonssyndrome.com)
(Robynne and Chris Warner)
As there are very strict rules in Australia on the importation, manufacture and supply of therapeutic goods, we advise you direct your query, in consultation with your physician, to the Therapeutic Goods Administration (TGA) of Australia. Their toll free number is 1800 020 653.
How do I make tablets for medicine, and what is the procedure?
(Roy)
This is a general question, and different manufacturers of tablets and medicine have different procedures and equipment. May we suggest you contact directly some of the local pharmaceutical manufacturers, and they may have information with flow diagrams to answer your question more effectively. Companies such as SmithKline Beecham, Novartis, Johnson and Johnson, and Herron are just a few names to pursue.
What tablet is carbamazepine and what is it for and what does it have in it?
(Dianne Coggan)
The chemical formula for carbamazepine is C15H12N2O. It is a therapeutic drug used as an anticonvulsant, specifically in the treatment of pain associated with trigeminal neuralgia. A reference document to visit for more detail is H Y Aboul-Enein, A A Al-Badr, "Anal.Profiles Drug Subs", Vol 9, p87-106 (1980).
How can I determine the volume of the gas released by one tablet of Alkaseltzer?
Design an experiment to test the effect of amylase on starch.
Education - Answers
I am doing a project on dry ice. My partner and I cannot think of any labs to do on dry ice. I was wondering if you had any ideas about labs that we can do on dry ice.
(Paul Goetsch)
Try the following, and remember when using dry ice the hazards, and wear gloves and safety glasses.
Take a tall measuring cylinder and fill it with water. Add a little dilute NaOH to the cylinder of water, enough to make the pH relatively high (11/12 - universal indicator paper would be violet). Drop in some dry ice, then stand back and enjoy the show! The effect you will see is a change in pH from alkaline to acidic, and on the way there will be billows of vapour emitted along with spectacular colour changes as the pH changes. You can repeat this experiment using a different indicator (such as Congo Red) to watch a different rainbow of colours.
Another simple experiment is to physically demonstrate the sublimation process of dry ice. That is, dry ice is solid and does not go through a liquid phase, but directly to the gas phase. So, take a flat balloon and put some dry ice in it, tie a knot in the balloon and watch it inflate.
I am planning a project with a class and I need to create a small explosion that will tear paper into lots of little pieces. My friend wants to use two firecrackers in a plastic bowl with the paper and place a lid loosely on top. Is there a better, safer way or would this work okay?
(Sue Carr)
It is more likely that a firecracker will burn paper, and not tear it.
Provided the paper is stretched tort without any other way for the expanding
gas to escape, any small explosion would cause the paper to tear. If you
only want to cause a loud sound, covering a bowl of vinegar which has a
cup containing Bicarb of Soda with plastic will work. Bump the bowl to knock
over the Bicarb so that it mixes with the vinegar. These reagents will react
to form Carbon Dioxide, which will expand against the plastic causing it
to break with a pop.
How can I determine the volume of the gas released by one tablet of Alkaseltzer?
(Carlos Flores)
You will need a beaker, a small glass funnel, a measuring cylinder, some plastic wrap, water and the Alkaseltzer tablet. Put the tablet in the bottom of the beaker and then put the funnel (upside down) over the tablet. Fill the measuring cylinder to the brim with water and cover the top with plastic so you don't lose any of this water for a step later. Carefully add some water to the beaker, about to the level half way up the stem of the funnel, ensuring NO water gets under the funnel and starts dissolving the tablet. Now the tricky bit: Carefully invert the full measuring cylinder and place over the funnel, piercing the plastic with the tip of the funnel stem. As water reaches the tablet, it will start to dissolve and emit gas. The additional gas will force itself up the stem of the funnel and into the measuring cylinder, displacing the water. When the reaction has finished, you will be able to determine the volume of gas emitted from the reaction by the total amount of water displaced from the measuring cylinder.
CaCl2 + Na2CO3 react to form CaCO3 + 2NaCl. I do not know how to determine the number of moles of sodium carbonate used in the reaction or how to convert that value to particles of sodium carbonate.
(Jason Sevier)
You already have a balanced equation with this information. So only one mole of sodium carbonate will react with one mole of calcium chloride. However, both these starting salts are solid substances. So the reaction requires the salts to be as aqueous solutions for the reaction to occur. Then you will result in a solution of NaCl and a precipitate of calcium carbonate. To convert your resulting carbonate into number of particles, you need to multiply the number of moles by Avogadro's number, or the number of molecules per mole of compound. In this instance there is just one mole, so the number of molecules will be Avogadro's Number: 6.22exp23
Design an experiment to test the effect of amylase on starch.
(Mac O'Neil)
ANSWER:
Materials: saliva, saltine crackers, test tubes, droppers, Iodine in KI solution (I2/KI), hot plates or incubator at 37C, beaker, water, test tube rack, thermometer
Before you design your experiment, it is important to be very clear about the question that you are trying to answer.
Starch is present in lots of the food we eat. Starch molecules are very large. Each one is made up of hundreds of much smaller molecules of a chemical called glucose, which have joined together.
Amylase belongs to the group of chemical compounds called enzymes. It is the job of enzymes to speed up chemical reactions in the body and amylase speeds up the breakdown of the very large starch molecules into the smaller glucose molecules.
The question you are trying to answer then is "does amylase break down the large starch molecules into smaller glucose molecules"
You can now work out what you will need to carry out the experiment:
something with starch in it (the saltine cracker)
a way of testing to show the saltine cracker contains starch ( the iodine in potassium iodide solution (I2/KI) is used to test for starch. It changes from pale brown to a blue/ black colour if starch is present.
something to test and see if any glucose has been made (Benedict's solution goes from blue to an orange colour if glucose is there.) OR you can test at the end of the experiment and show that the starch (or most of it) has gone by testing a little of your reaction mixture with the iodine in potassium iodide solution. If you can iinclude Benedict's solution on the list of materials you can use, then this is probably the easiest.
a source of amylase. Saliva cannot be used as a source of amylase any more in schools, so if you are actually going to do this experiment you will need to ask for a solution of amylase.
We need to be able to do this reaction to see if it takes place at the temperature of out bodies (37C) so you need some way of getting to 37C (incubator or hot plate + beaker of water)) and some way of knowing that the temperature is 37C (thermometer).
something to carry out the reaction in (test tubes)
EXPERIMENT:
ß Half fill a beaker with water (to act as a water bath) and put it on the hot plate to heat to 37C. Check the temperature of the water regularly and adjust the hot plate so that the temperature stays as close to 37C as possible - (alternatively turn on the incubator and set to 37C)
ß Scrunch up a little of the saltine cracker and put into a clean, dry test tube. Add a little iodine in potassium iodide solution using a pipette and watch what happens. This is to test for starch.
ß Scrunch up a saltine cracker and pack the pieces into the bottom of a clean, dry test tube. Just cover with a little water. Now put a little amylase solution into another clean, dry test tube.
ß Put these 2 test tubes into the water bath or incubator for a few minutes until they reach a temperature of 37C. Check this with the thermometer. (remember to rinse the thermometer with water between readings so that you don't contaminate the contents of either tube).
ß When both tubes are at 37C, pour the amylase solution into the saltine cracker + water and replace this tube in the water bath or incubator. Leave for 10 minutes. It is important to keep it at 37C.
ß After 10 minutes, remove a little of the mixture with a pipette and put into another clean test tube. Put your reaction tube back into the water bath or incubator in case you need to leave it for longer..
ß Add a few drops of Benedict's solution to the sample of your reaction mixture and put this tube in the water bath too - Benedict's works better if heated. This is to test to see if any glucose has been formed. (if you do not have Benedict's solution, then repeat the starch test to see if the starch has gone ).
ß If there has been no change, leave the reaction mixture at 37C for another 10 minutes and test a sample again. Repeat this until you can prove a change has taken place, or until you are sure there is not going to be a reaction.
ß Experiments should always be repeated to check that they give the same result. You could repeat this (which could be a bit boring) or work with more than one sample from the beginning making sure you treat them all in the same way. Or, if you work in a group, each member of the group can set up one experiment (you can all use the one water bath) but be careful that you all do the experiment in exactly the same way.
ß Write down your observations at each stage of the experiment. Remember to say what things look like originally as well as what they look like afterwards.
Having carried out the experiment and looked at the observations you should now be able to answer the question that the experiment was designed to answer. Of course, you will need to find a way to record all this!
How does the deodorisation process work for esters?
Environmental Chemistry - Answers
How does the deodorisation process work?
(Dave Shivas)
Because these compounds (esters) are sweet-smelling, they are used as deodorisers. They mask or over-power bad odours. They are used in toilets, cars, food flavourings and cosmetics. One very characteristic methyl ester is methyl salicylate (derived from methanol and salicylic acid) which provides the smell in "Dencorub" and similar exercise rubs.
Does the term BOD really refer to the biological oxygen demand or is it in fact the biochemical oxygen demand. (Does the biochem oxygen demand = biological oxygen demand + chemical oxygen demand?)
(Faeire Hay)
In short, the Biological Oxygen Demand is the same as the Biochemical
Oxygen Demand. It is a measure of the amount of living organisms contained
in an environment. Chemical Oxygen Demand is a measure of the amount of
oxidisable organic material in an environment.
What is the EXACT chemical formula of a cup of coffee (minus the cup of course)?
Food - Answers
What is the chemical formula for vinegar and baking soda, and what is the chemical equation when the 2 react?
(Moh'd)
Vinegar is a dilute (4-10%) solution of acetic acid, or ethanoic acid, with the chemical formula CH3COOH.
Baking soda is Sodium Bicarbonate with the chemical formula NaHCO3.
The chemical equation when these 2 react with each other is:
CH3COOH + NaHCO3 ----> NaO2CCH3 + CO2 + H2O (sodium acetate + carbon dioxide + water)
Can you explain more on PDI and NSI of soymeal? Is there a conversion factor that you can use on PDI to convert to NSI? What would soymeal with a low PDI and NSI be used for?
(Krity Miller)
NSI is Nitrogen Solubility Index; PDI is Protein Dispersibiltiy Index. For extra information refer to http://www.ruchihealth.com/nutrela/soya.html (obtained by a www.google.com search). Refer to the American Association of Cereal Chemists (AACC) Methods for procedures. There is possibly some relationship between NSI and PDI but these methods are probably method dependent (ie type of extraction solvent, time, temperature). It is understood that high NSI is required for high digestibilty which is important in animal feeds.
Could you explain in terms of chemical bonding why polyunsaturated compounds (which contain many double and/or triple bonds are better for a person's health than saturated compounds (which contain no double or triple bonds) ?
(Rachel Christopher)
In terms of chemical bonding, polyunsaturated compounds (those with multiple double or triple carbon-carbon bonds) are better the saturated compounds (those without any double or triple bonds) because the double or triple bonds are able to react with compounds that are detrimental to health.
What is the EXACT chemical formula of a cup of coffee (minus the cup of course)?
(Maria)
Coffee beans do not have an EXACT chemical composition, therefore it is impossible to answer your question. However, in general, a coffee bean constitutes the following:
So, you then further complicate your exacting question when taking into account
a) the water added: water will vary around the world, depending on local sources and treatment before issued for consumption (eg: salinity, flouride added, mineral content, etc).
b) if milk is added: is it cow's milk, and if so, what type (full cream, calcium enhanced, etc)? And similar complexities arise when considering the options of other sources of milk, such as goat, sheep, human, and soy.
And we didn't even get started on the various types of sugar available, let alone how varying quantities of sugar may affect the overall chemical formula of the drink. Are you getting the picture yet?
So far we have not received any questions on this topic.
What are the products and reactants when you burn coal?
What substances is gasoline composed of? Which of these substances make it flammable?
Fuel Technology - Answers
What are the products and reactants when coal burns?
(Cheryl)
Given the complex chemistry of coal, there is not a simple answer to your question. However, we will attempt to simplify it as follows:
Coal is formed by arrested bacterial decay of vegetation that grew 40-300 million years ago, followed by chemical processes of condensation and polymerisation under the influence of temperature, pressure and time. Due to these variables, coal is ranked according to carbon content (from ~50 - 95%), with the highest ranking coal being called anthracite. So the properties of the various ranking coals will vary considerably. Therefore, to address the part of your question on the reactants, in general, the reactants will be the coal (carbon, inorganics, impurities), oxygen as a fuel, and temperature.
The products from burning coal will depend on all three parameters (coal, temperature and oxygen content). However, in general you will get carbon dioxide, carbon monoxide, water and various impurities, the most common being sulfur dioxide. There are well known environmental issues with the burning of coal, the main ones being a) acid rain from the sulfurous impurities, and b) dust or soot as the oxides of the various burnt inorganic matter.
What would happen if cellulose is heated in a high pressure chamber containing Hydrogen? Would it create coal? I am assuming that the oxygen will combine with hydrogen creating water and the hydrogen would contribute to the hydrogen in the chamber.
(Barrington Murray)
It is unlikely that coal would be created with the mixture being heated and pressurised, the probability of chemical reaction / change is high, particularly in the formation of a suite of hydrocarbon products. The most likely scenario is a mish-mash of hydrocarbon products over a broad spectrum of molecular families but not specifically those associated with coal. I personally would expect many compounds which might be common to crude oil, there will be degradation and reforming processes taking place, there could be "water gas" formation at some stage in the process and further there may be some reforming (particularly with the excess hydrogen). Ultimately there may be a few "coal type" products produced in the reaction vessel but this is not what could be considered as an ideal pathway to coal production.
What substances is gasoline composed of? Which of these substances make it flammable?
(Tshwanna Littles)
The overall composition of gasoline may vary, depending on the processes available, but the main component is generally a straight-run naphtha from the primary distillation of crude oil. And all components are flammable.
A series of Oxygen Solubility questions
Gases - Answers
What organic substances in emission gases are emitted into ambient air during manufacturing of ethylene chlorohydrin?
(Vaclav)
We advise you contact a company in this industry, but if chlorine followed by water are added to ethylene to give the chlorohydrin, the by-product will be HCl. Depending on how the process is done, this could be emitted into the atmosphere or, more likely, just dissolve in any water present.
A series of Oxygen Solubility questions: a)Why does oxygen have such a low solubility in water? b) What effect does temperature have on the solubility of a gas solute in a liquid? c) What molecular interaction is responsible for oxygen dissolving in water? d) What molecular interaction occur between oxygen and perfluorocarbon molecules?
(Jarod)
a) Water has Van der Waals forces / Hydrogen Bonding and the water molecules are attracted to other water molecules. Solubility of O2 from air is 9 mg/L (9ppm) and pure oxygen is 45 mg/L (45 ppm) - proving Henry's Law (solubility is proportional to partial pressure).
b) Increasing temperature reduces solubility.
c) Oxygen is non-polar - water prefers ionic species.
d) Perfluorocarbons would have an affinity for the non-polar Oxygen.
So far we have not received any questions on this topic.
How does the electrolysis of tarnished silver work?
Can you help me determine the molecular mass of a number of various steel alloys?
Does boiling water remove Fluoride?
Why is carbon mixed with iron in the manufacture of Steel? What type of new bonds are formed?
I want to know how baking soda works to clean? What is the chemical reaction?
Inorganic Chemistry - Answers
How does the electrolysis of tarnished silver work?
(Laura)
Tarnished silver is elemental (pure) silver coated with a layer of Ag2O. The electrolysis process converts this oxidised silver back to elemental silver via electron transfer, using electricity as the source of electrons (sometimes by REDOX). So:
Ag+ + e- -------> Ag(s)
I need help to find out what the average molecular mass of these alloys are Carbon steel, Cast iron, Manganese Steel, Common steel, Tungsten Steel, and Silicon steel. If it helps Carbon steel is a combination of carbon, silicon, iron, and manganese. Cast iron is a combo of carbon, manganese, iron, and silicon. Manganese steel is a combo of iron, manganese, and carbon. Tungsten steel is a combo of iron, tungsten, and carbon. Common steel is a combo of iron and carbon. Silicon steel is a combo of iron, silicon, and carbon. I like through various websites and books but I could not find out the info I needed. Any help will be greatly appreciated. If you cannot tell me exactly what the average molecular mass for the alloys are can you at least direct me to a website where I can find the information.
(Jeremy)
The difficulty for a chemist with your question is that metals and alloys do not have a molecular mass (or a molecular formula) in the same way that water or chloroform do. This is because metals are not molecular (ie consisting of discrete molecules). Nor are they like a pure ionic compound such as sodium chloride which has a 3-dimensional lattice of positive sodium ions and negative chloride ions. The best information that can be given on an alloy is a percentage composition (which you have found). I would strongly suggest that you use another factor (eg the % of various alloying elements: Mn, W, Cr, Mo, V, Co, Ni etc) as part of your study.
Does boiling water remove Fluoride?
(S Eadie)
Boiling normal tap water would not remove fluoride because fluoride does not evaporate - it would be left in the small salt residue left behind when water is boiled dry. Putting this fact to use...
If you boiled the water and condensed the steam back to liquid water in another container, then the condensed water would contain only a trace of the original fluoride.
Why is carbon mixed with iron in the manufacture of Steel? What type of new bonds are formed?
(Fahad Fahsher)
Carbon is added to steel to increase its tensile strength (making it
more difficult to break). There are no bonds formed between the Carbon and
Iron. On close inspection (using a microscope) it is clearly visible that
the carbon forms small granules in the iron.
I want to know how baking soda works to clean? What is the chemical reaction?
(Robin)
Baking soda is probably not a very good cleaner but it would be OK for 'moving' fats, oils and grease base dirt as the 'acid' should tend to split off the "fats" when cleaning.
2NaHCO3 + Fatty acids (ie the grime) = Na salt of the fatty acid + 2CO2 + 2H2O
The CO2 evolution would also tend to lift the grime
The sodium salt of the fatty acid is in fact a 'soap' type compound which would facilitate the cleaning process.
Please give me the chemical formulations for the following:
(Jessica Bedell)
Formulae:
Does polyester or its monomer have any environmental hazards?
Does polyester or its monomer have any environmental hazards?
(Jennifer Jean)
More information is required on the type of polyester you are investigating. However, for all questions of this nature, we refer you to the Material Safety Data Sheet for the specific product in which you are interested. A web site of MSDS's is quoted at the top of this page.
What exactly are methyl esters?
Name a poly-atomic ion composed of one hydrogen atom, carbon and three oxygen atoms.
Can you please inform me on the theory of Emulsions?
Can you please give me some examples of esters, their occurence, production and use?
Are there any coloured surfactants?
What is the equation for the reaction that occurs when vinegar is added to ammonia (NH3)?
I was wondering if you could tell me how you would make luminol for a science experiment.
Provide details of the manufacturing process of 3-nitrophthalic acid
What are the mechanisms used in the manufacture of high density and low density polythene?
What is Phenyl and what does it look like?
What are the principles and scope of recrystallisation and solvent extraction methods?
Organic Chemistry - Answers
What exactly are methyl esters?
(Dave Shivas)
Esters are sweet-smelling compounds made from carboxylic acids and alcohols. Carboxylic acids are sour-smelling compounds, the simplest of which are formic acid (the smell of crushed ants) and acetic acid (which is actually vinegar). Methyl esters are those esters which are formed from the simplest alcohol methanol.
Name a poly-atomic ion composed of one hydrogen atom, carbon and three oxygen atoms.
(April)
Hydrogencarbonate or bicarbonate (older)
(Kenneth Davies)
A polymer is a high molecular weight molecule that is made up of repeating molecular units (monomers). Some polymers are synthetic (nylon, polystyrene, etc.) while others are derived from natural systems (starch, proteins, DNA etc.). The polymers deriver from natural systems are called biopolymers.
Can you please inform me on the theory of Emulsions?
(Eliza Ritchie)
Emulsions are colloidal dispersions of two immiscible liquids, or liquids that are not soluble in each other. So, as an example, vinegar is mostly water. When shaken with a salad oil, as in the preparation of a salad dressing, a temporary oil-in-vinegar emulsion is formed. This quickly separates into a layer of oil and a layer of vinegar. On the other hand, mayonnaise is also an oil-in-vinegar emulsion in which the egg yolks, a colloidal material, act as an emulsifying agent that stabilises the dispersed oil droplets with a protective film that prevents their coalescence. Another good example is that of soap which is a classic emulsifying agent in that it can emulsify oily dirt so that it can be rinsed away.
Can you please give me some examples of esters,
their occurance, production and uses?
(Kate)
a) Methyl Salicylate (or oil of wintergreen) has the chemical formula C8H8O3. It is prepared mostly by esterification of salicylic acid with methanol and is present naturally in the leaves of Gaultheria procumbens and in the bark of Betula lenta. Methyl Salicylate is used in perfumery and for flavouring sweets, as well as a therapeutic use as a counter-irritant.
b) Ethyl Acetate (or acetic acid ethyl ester, or vinegar naphtha) has the chemical formula C4H8O2, and is obtained by slow distillation of a mixture of acetic acid, ethyl alcohol and sulfuric acid. Its uses are varied, and include a pharmaceutical aid (flavour); artificial fruit essences; solvent for nitrocellulose, varnishes, lacquers and aeroplane dopes; cleaning textiles, and more!
c) Ethyle Acrylate (or acrylic acid ethyl ester) has the chemical formula C5H8O2, and is prepared from ethylene chlorohydrin or acrylonitrile, ethanol, and sulfuric acid; also by an oxo reaction from acetylene, carbon monoxide and ethanol in the presence of suitable catalysts. Ethyl Acrylate is used as a monomer in the manufacture of water emulsion paint vehicles, in the production of emulsion-based polymers used in textile and paper coatings, leather finish resins and adhesives, and imparts flexibility to hard films.
Are there any coloured surfactants?
(Ekta Mahajan)
The simple answer to this is NO!
What is a household product that is a) made of polar molecules, b) a hydrocarbon with a molecular weight of 100 or more, and c) made of Sodium Carbonate?
(Brittni Vorrhis)
a) Water
b) Moisturising creams, olive oil
c) Alkaseltzer (ant-acid tablets), some washing powders
With the condensation polymers, why are they called 'condensation'? Does that indicate the production of water specifically?"
(Yvonne Kavatina)
Response from Whelan, Tony, Polymer Technology Dictonary, Chapman
and Hall, London, 1994. "Condensation Polymerisation
: Also known as polycondensation. Polymerisationin which monomers are
linked together with the splitting off (elimination) of water or other simple
molecules to give a condensation polymer."
What is a solid substance that does not dissolve in water, does not conduct electricity, and does not melt below 1500 degrees celsius? Label with Formula and bonding type.
(J Stewart)
Our chemists were not sure of the context of your question, so the only answer they can give you is that CARBON does not dissolve in water, nor conducts electricity, and melts at 3550C.
After a reaction, I have to distill ethyl acrylate. How do I clean everything and eliminate the odor?
(Ramiro Rivero)
Using a fume cupboard, we suggest you flush all equipment thoroughly with acetone.
What is the equation for the reaction that occurs when vinegar is added to ammonia (NH3)?
(Chris Athanasias)
This is a reaction in which a weak acid (Acetic acid in vinegar) reacts with a weak base (Ammonia). As a result, the reaction does not proceed to completion. Instead it comes to an equilibrium, a point where the rate of the forward reaction is equal to the rate of the reverse reaction. This is shown schematically below:
CH3COOH + NH3 <--------> CH3COO- + NH4+
All the nonpolar solvents I read of which are used in herbal extractions (such as hexane with saw palmetto) appear to be somewhat toxic. Can oils (such as olive oil) serve as nonpolar solvents for extraction purposes, and if so, why aren't they more widely used?
(Robert Manson)
Yes, oils can be utilised as non-polar solvents for extractions. They are not widely used for this purpose due to their high viscosity. The extraction technique most often employed is liquid-liquid phase extraction, which relies upon the immiscibility of the 2 liquids as well as their low viscosity for rapid separation after mixing.
I was wondering if you could tell me how you would make luminol for a science experiment.
(Cashida Okeke)
Here is a website that you might want to visit which will answer your question: It is entitled Chemiluminescence: Synthesis of Luminol
http://cas.bellarmine.edu/chem117a/lab/luminol.htm
Provide details of the manufacturing process of 3-nitrophthalic acid
(Dr Gouri Muju)
The answer given here is for a laboratory scale technique. We suggest you visit web sites of manufacturers of 3-nitrophthalic acid for further information. Often commercial information is not available for obvious reasons of competition and fair trading.
3-nitrophthalic acid can easily be prepared by nitrating phthalic acid. A solution of phthalic acid in glacial acetic acid is prepared. To this is added concentrated sulfuric acid, followed by nitrating acid, a 40:60mixture of conc. nitric acid and conc. sulfuric acid. During the addition of the nitrating acid the temperature MUST be kept below 5oC. The reaction mixture is then poured into ice/water, and the solid product is collected by filtration, and purified by recrystallisation.
How has Organic Chemistry changed our daily lives? What are five different products made in this field that we use in our daily lives that were not around 50 years ago?
(Lacy Moo)
Organic chemistry has changed our everyday lives by allowing production
of many useful materials on a large scale. In answer to providing 5 new
products, we have listed four general areas, in which there are several
specific examples. a) Medicines: the discovery and development of antibiotics,
b) Polymers: Many objects in use are polymers, for example teflon which
is used in non-stick coatings on cooking utensils, c) Food Flavourings:
There are now many synthetic versions of natural flavours, which allows
for mass production and a cheaper product. For example, the natural Vanilla
Extract is far more expensive than its synthetic equivalent, Vanilla Essence,
d) Dyes and Paints: The range of colours available in dyes and paints has
expanded greatly in recent years.
What are the mechanisms used in the manufacture of high density and low density polythene?
(Dustin Engen)
Firstly, there are several types of commercial technologies available for manufacturing the wide range of Polyethylene plastics. In general, there are high pressure / high temperature processes (eg: autoclave) through to safer low pressure / low temperature processes. The density of the Polythene is "high" or "low" depending on the side chain branching along the polymer. In many instances a catalyst is required to initiate the reaction, and then, depending on the specific type of Polythene the manufacturer is producing, the density may be affected by the physical reaction conditions, and/or the addition of other chemicals such as a monomer or comonomer. Also, varying concentration mixes of all raw materials will in turn have an impact on the density of the polymer produced. If you are after more detailed information, one suggestion is to contact local manufacturers of Polythene, Qenos. They have locations in both Sydney and Melbourne.
What is the condensed structure for an ester with a pineapple odour is produced from ethanol and butanoic acid?
(Veeps)
Ethyl butanoate, the ester in question, has the condensed structural formula of CH3CH2OCOCH2CH2CH3.
I have two questions about the reaction between vinegar and bicab soda. 1.What gas is produced when vinegar and bicarb meets? 2.What are actually molecules?
(N. Sadrina)
The reaction between vinegar and bicarb. soda (sodium hydrogen carbonate) can be represented as follows:
CH3CO2H + NaHCO3 -------¦ CO2(g) + H2O + NaO2CH3(aq)
Acetic bicarb. carbon water sodium acetate
Acid soda dioxide
A molecule is the smallest particle of matter which can exist in a free state. So for a substance such as sodium chloride, the molecule is considered as NaCl.
What is Phenyl and what does it look like?
(Aaron Markveld)
Firstly, there is no such chemical called phenyl. Rather, phenyl is the family name for all chemicals with the group C6H5. PHENOL however, has the chemical formula of C6H6O, and is commonly denoted as PhOH (that is, a phenyl or benzene ring with a functional group OH on it). Phenol is a colourless crystal, melts at 43C, boils at 183C, and is soluble in water at room temperature. Phenol is acidic and forms metallic salts.
What are the principles and scope of recrystallisation and solvent extraction methods?
(Andrew Somers)
Both recrystallisation and solvent extraction are techniques that are mostly used as purification methods for synthetic products.
Paint - Answers
We make an ink that is an emulsion of mineral oil and water. At temperatures below -11 degrees C it is damaged--it separates. Can you suggest anything we can add to the ink to permit it to be stored at lower temperatures?
(Robert Keen)
Our expert's suggestion would be to add a thixotropic additive to stabilise the emulsion. A product called "BENTONE" is used for such applications, but there are various such additives on the market. "BENTONE" has been used for improving the stability of ink, paint and adhesive emulsions. There are various grades to suite specific applications. BENTONE is a proprietary product and is a compound made from reacting amines with Bentonite clay. When included in paint, ink and adhesive formulations it provides a 'lattice' structure to the product which thickens the product but also gives slip (thixotropy). The principal of thixotropic additives is to 'thicken' the product so that it is quite 'thick' in the can but becomes 'thin' when in use due to the thixotropy. Thus, an emulsion (or a single phase solution mixture) can be given good stability due to the increased 'thickening' but remain quite 'thin' in application. This is a common method used in the paint, ink and adhesive business.
How can you determine whether a molecule is nonpolar or polar via its shape?
Periodic Table - Answers
I can't understand the concept of molecular polarity. How can you determine whether a molecule is nonpolar or polar via its shape?
(Laarni)
A bond is polar because there is a difference in electronegativity (ie pulling power of an atom for electrons) between the partner atoms in the bond. The difference in electronegativity means that the shared pair of electrons in a covalent bond is evenly shared so one atom will have a partial +ve charge and the other atom will have a partial -ve charge (ie a dipole). So most BONDS are polar because atoms of different elements are involved. However to decide whether a MOLECULE is polar, we must consider the shape and determine whether the dipoles associated with the bonds are cancelled out to give a non-polar molecule or if the dipoles are not cancelled then the molecule will be polar.
A C-O bond will be polar because O has a higher electronegativity than C. However CO2 is not a polar molecule because the two C-O dipoles cancel each other in this linear molecule (think in terms of vector addition). An O-H bond is polar because O has a higher electronegativity than H. H2O is a polar molecule because it is not linear, cancelling of the two dipoles does not occur and the molecule has a net dipole.
How do I determine the melting point of an element based on the elements that are placed before it. For example, fluorine is -220C, chlorine is-103C, and bromine is ?
(Austin Debevec)
Due to the periodicity of the chemical and physical properties of the elements, the periodic table was able to be constructed. If a group of elements is selected (say group 1, the alkali metals) and a graph is constructed of the property of interest versus the atomic mass of the elements involved, an unknown value for that property can be extrapolated. It is necessary thought, that at least three data points be known, so as to ensure a more accurate estimate.
An example of this can be seen from the melting points of the group 1 metals. The melting point of Francium is not mentioned. Graphing the following data will allow it to be determined.
Element Atomic Mass (AMU) Melting point (C)
Li 7 180
Na 23 98
K 39 63
Rb 85 39
Cs 133 28
Fr 233 ??
A graph of the atomic masses of the elements against their melting points, along with a line of best fit, shows that the melting point for Francium is approximately 21 C. This would make it the third liquid element at room temperature.
I need to make a Bohr model of an atom. I chose Uranium. a) To which family does U belong, and which period? a) How many electrons go on each energy level?
(Daniel Biegler)
The Bohr model of the atom states that the atom is composed of a small positively charged nucleus of protons and neutrons surrounded by negatively charged electrons. The electrons are contained in "shells", "sub-shells", and "orbitals." The number of electrons exactly matches the number of protons, so that each atom is electrically neutral. In the case of Uranium (U,) the number of protons and electrons is 92. The number of neutrons in the nucleus is dependent on which isotope is being examined. For 238U, the most stable isotope, the number of neutrons is 146.
a) U belongs to a group of elements called the "transuranics" which also includes elements like Plutonium and Neptunium. All of these elements have similar chemistry, and are quite difficult to separate. The transuranics belong to the seventh period. (Each row in the periodic table is a period, and each column is a group.)
b) The electronic configuration of U is shown below in terms of shells, sub-shells and orbitals (and the number of electrons in each sub-shell):
Shell 1 2 3 4 5 6
Sub-shell 1s 2s 2p 3s 3p 3d 4s 4p 4d 5s 5p 5d 5f 6s 6p 6d
# Orbitals 1 1 3 1 3 5 1 3 5 1 3 5 7 1 3 5
# electrons 2 2 6 2 6 10 2 6 10 2 6 10 14 2 6 6
In the 6d sub-shell, there are 5 orbitals that are occupied by only 6 electrons. According to the Aufbau principle, electrons will fill a set of orbitals in such a way that the maximum number of unpaired electrons will exist (i.e. the orbitals will be half filled) before they will pair electrons (fill the orbitals.).
To construct a Bohr model for Uranium (238U,) you will therefore need a nucleus containing 92 protons (say red marbles,) 146 neutrons (say white marbles,) surrounded by 92 electrons (say blue pebble sized objects) arranged in at least 6 levels (shell levels.)
An easier Bohr model to construct would be Hydrogen (H.) For this you only need 1 proton and 1 electron. To build a scale model would be difficult. As an illustration of the Bohr model, imagine a cricket ball at the very centre of the SCG or MCG, this would be the proton nucleus. The electron surrounding this would be the size of a pinhead and would be whizzing around about the boundary rope.
Could you offer a method for differentiating between chloride and bromide in plastic samples?
Plastics and Polymers - Answers
I am looking for some kind of a method or instrument to differentiate between chloride and bromide. The reason I am looking for something to do this is because I am employed at a plastic extrusion company and we run fire retardent materials which contain bromide. When we test our materials in our lab we do a flame test by burning some of the materials. When it is a fire retardent material a green flame is given off but we also get a green flame from polyvinyl chloride. The PVC is a contaminate and will burn up the chrome on our dies if it some how gets mixed in with other materials. The materials will come to our lab in a pellet form so we need some kind of method or instrument to take us from the pellet being a green flame to a positive identification of the material as containing either chloride or bromide. If you could provide any information it would be greatly appreciated.
(Joe Jacobsen)
Joe, as a part of my undergraduate degree many years ago I did considerable work on the organic halides in gaseous form and my tool was Infra-red ( and I could use it both qualitatively and quantitatively). There are some strong areas in the spectrum in the range of 550 - 800 cm -1 with the chlorides towards 800 and the bromides towards the 550 cm -1.The exact location of the peaks is affected by the attached organic structure, so it is a matter of examining the actual materials that you are using. Having noted that I would suspect that Mass-spec may also be a useful tool to try.
Now, my interests have been Industrial Chemistry where we would be interested in the area in which to look but we would tend to run spectra of the 100% PVC and the Bromide and then "dope up samples in the intermediate range" to provide an indication of the peaks and what we are looking for. With a chart for our operators which would provide a qualitative pass / fail indication as a QC step for feedstock.
Here, my interest in Chemical Engineering comes foreward, my approach would be to examine the properties of our dies and seek a plating material which may not be damaged by chloride contamination. I do not know if it is possible but I have had considerable success with Titanium, when it comes to resistance to halogens, particularly chlorides. I would tend to prefer going this way and then not have to worry about contamination by chlorides, in fact it may be a pathway to obtaining a cheaper feedstock where chloride contamination is a risk which could then be ignored or at least will not have such a detrimental effect on equipment.
So far we have not received any questions on this topic.
I'd like to ask my own question. |
Why isn't the formula of the hydronium ion H4O++?
Does the colour of water affect its boiling point? Why or why not?
Water and Water Treatment - Answers
Why isn't the formula of the hydronium ion, H4O ++ ? This seems logical because of the two pairs of non-bonding electrons in water and the small size of the captured protons.
(Louis Bialy)
When an acid dissosciates in water, the Oxygen of water donates one of
its lone pairs of electrons to the Hydrogen(+) cation, forming a co-ordinate
covalent bond. This leaves the Oxygen with reduced electron density, and
the single positive charge. The electronegativity of oxygen is quite large.
It is, in fact, the second most electronegative element. As a result, the
loss of electron denisty is not favourable, and the remaining lone pair
electrons are even more tightly bound.
In a text book I read "the covalent molecualr gas Hydrogen Chloride is very soluble in water because it forms ions H+ and Cl-. This is ionisation and the ions are formed due to the reaction with water". What reaction are they talking about that causes a covalent molecular gas to decide to form ions?
(Rachel Christopher)
Although HCl is covalently bonded, the difference in electronegativities results in the bond being strongly polarised. The lone pair electrons of the water-oxygen can form a coordinate bond with the H of HCl. This then allows the H to donate its electron to the Cl, resulting in Cl-. H+ does not actually exist in solution, instead it forms the hydronium ion (H3O+) with water.
Does the colour of water affect its boiling point? Why or why not?
(Tierra Walker)
Water is a clear colourless liquid. Any colour therefore, comes from impurities. A solution such as impure water does have a slightly higher boiling point than pure water, but unless the solution is somewhat concentrated, this difference is not noticeable. This effect is known as boiling point elevation, and is accompanied by freezing point depression (i.e. the solution freezes at a lower temperature than pure water.) These are colligative properties, which means that the extent of these properties depends on the concentration of the solution.
Does a chemist always work in a chemist shop?
Do chemists ever end up working outdoors at all, or do most chemists work indoors in labs?
How does the enthalpy or potential energy of the products compare with that of the reactants?
What is the reaction between hydrogen chloride gas and water?
Why does the Bronsted-Lowry Acid/Base theory work for substances like ammonia, but not benzene?
What is electronic configuration and how do you work it out?
Why is the melting point low when the atomic mass is low? Is there a relationship between the two?
What is the melting point of NaCl?
How do you measure Density using Archimedes Method?
I would like to know the boiling point of tri-isopropylbenzene.
OTHER - Answers
Does a chemist always work in a chemist shop?
(Nigel Rose)
This is a good question, Nigel. In fact, your local chemist shop is properly
called a Pharmacy, and Pharmacists work in a pharmacy, not Chemists. A Chemist
does a wide range of things from research and development to analysing all
sorts of samples (like rocks, food, petrol, cosmetics, even gases) to marketing
a product for a company. Basically, a chemist could be working in a laboratory
developing new drugs, materials or experiments, or managing companies that
perform these tasks!!
Do chemists ever end up working outdoors at all, or do most chemists work indoors in labs?
(Ben Murrin)
All chemists, if practising their profession, by nature of the job have to work in a laboratory to conduct various experiments. However, there are several jobs where the chemist is required to collect samples, which may only require a brief visit outdoors to a sample point on a factory, or may require field work along with other scientists to inspect the environment, design an experiment, and then collect appropriate samples. This might involve many days away from the laboratory for any one series of experiments. So they are not always confined to the laboratory.
How does the enthalpy or potential energy of the products compare with that of the reactants?
(H Couch)
Enthalpy (H), is defined as a thermodynamic state function, H = U + PV,
where U us the internal energy and P and V are the pressure and volume respectively.
For any process that occurs at constant temperature, heat may be absorbed
or evolved, depending on the nature of the reaction. That is, you may be
dealing with an endothermic or exothermic reaction. If endothermic, then
heat is absorbed, and a spontaneous endothermic reaction must be accompanied
by an increase in entropy of the system and surroundings. If exothermic,
then heat is evolved.
:
I was reading my textbook and it said "the covalent molecular gas Hydrogen Chloride is very soluble in water because it forms ions H+ and Cl-. This is ionisation and the ions are formed due to the reaction with water." I was wondering what reaction are they talking about that causes a covalent molecular gas to decide to form ions?
(Rachel Christopher)
Although HCl is covalently bonded, the difference in electronegativities results in the bond being strongly polarised. The lone pair electrons of the water oxygen can form a coordinate bond with the H of HCl. This then allows the H to donate its electron to the Cl resulting in Cl-. H+ does not actually exist in solution, instead it forms the hydronium ion (H3O+) with water.
Is there a theoretical maximum Kelvin temperature? If so, what is the value and how is it calculated?
(Louis Bialy)
As far as we are aware, there is no theoretical maximum temperature.
However, you may wish to contact a physicist for more detail on this topic.
(Michael Starky)
Peptisation is a chemical means of forming a dispersion, which is the
reverse of coagulation. The dispersion is generally a colloidal sol in which
the particulate matter is stabilised by the adsorption of ions. For example,
silver iodide sols can be formed by shaking the neutral precipitate with
a small excess of either potassium iodide or silver nitrate. With the former
reagent the resultant sol has a negatively charged surface; with the latter
it is positively charged.
How is temperature related to particle movement? How would temperature effect the speed/rate of a reaction?
(Natasha Prow and Donna)
Assuming you mean atomic or molecular movement, and not particle movement, as temperature is increased, molecules will move faster. Hence higher temperatures, generally speaking, accelerate the rate of a reaction.
Why does the Bronsted-Lowry Acid/Base theory work for substances like ammonia, but not benzene?
(Karma)
This theory defines acids as proton (H+) donors, and bases as proton acceptors. Ammonia has a lone pair of electrons able to accept a proton, and so is classified as a base. However, benzene is not able to either accept or donate a proton, and hence cannot be classified in this way.
Can you please tell me all the bond angles with respect to both carbon atoms in ethanoic acid. How does one determine bond angles of different molecules.
(Safia Haider)
The formula for ethanoic acid is CH3CO2H. The bond angles around the methyl (the CH3) carbon are all 109.5 degrees. Whilst those around the carboxyl (the CO2H) carbon are 120 degrees.
To determine the bond angles, it is necessary to examine the regions of electron density around the atom, as well as the strength of electron-electron repulsions. Lone pair electrons exert more repulsive force than a pair of bonding electrons, thereby bending the bond angle.
For example, compare methane, ammonia, and water. Methane, CH4, has 4 regions of electron density, all of which form bonds. The bond angles will be 109.5 degrees. Ammonia, NH3, also has 4 regions of electron density, but one is a lone pair. This exerts a repulsive force on each of the bonding pairs that is greater than the force exerted by the other bonding pairs. Hence the bond angle is slightly less, at about 107 degrees. Finally, water has 4 regions, 2 of which are lone pairs. Each of these lone pairs squashes the bonding pair of electrons so that the final bond angle is only 105.9 degrees.
What is electronic configuration and how do you work it out?
(Kevin Day)
Electronic configuration is the arrangement of electrons into sub-shells and orbitals in an atom. It is determined by working out the order of sub-shell energies and the number of orbitals within each sub-shell (e.g. an s sub-shell has 1 orbital, a p has 3, a d has 5, an f has 7.) If the Pauli principle (no two electrons can occupy the same space) and the Aufbau principle (electrons will half fill a sub-shell before filling it) are applied, this helps to work out the electronic configuration. It is important to note, however, that the order of sub-shell energies can vary from element to element, and from atom to ion.
For example, elemental Iron, Fe, has 26 electrons, whereas Iron(II), Fe(2+) has only 24. The electronic configuration of elemental Iron is 1s2 2s2 2p6 3s2 3p6 4s2 3d6, while the electronic configuration for Fe(2+) is 1s2 2s2 2p6 3s2 3p6 3d6. This is an example of how the orbital energies can change.
I saw in my text book the general idea that the solubilities of most solid solutes in water increases as the temp of the solution goes up. Examples are NaNo3, CaCl2, Pb(NO3)2 NaCl, etc etc, But,...one example on the curve in the text showed a exeption, Ce2(SO4)3 Cerium Sulfate Its solubility decreases as temp increases! I would like to know why this molecule behaves opposite most.
(Jamey Licata)
The solubility of a salt depends on the dissolution reaction. In some cases (e.g. NaOH,) the dissolution of the solid into ions is a favourable reaction. In these cases, the dissolution releases heat, and is said to be exothermic. The solubilities of such salts decreases as the temperature of the solution increases. In other cases (e.g. KI,) the opposite is true, heat is absorbed as the dissolution takes place. This ia an endothermic dissolution, and solubility of these salts increases as the temperature increases.
It is possible to determine whether or not a dissolution reaction will be endothermic or exothermic by doing enthalpy (Delta H) calculations. Subtracting the delta H value for the parent salt from the sum of the delta H values for the aquated ions will tell you the enthalpy difference for the dissolution. If this value is negative, the dissolution is exothermic, whilst a positive value indicates an endothermic dissolution.
Why is the melting point low when the atomic mass is low? Is there a relationship between the two?
(Angel Johnson)
The melting point of an element bears no relationship to its atomic mass (A), The melting point for Lithium (A=7) is 180 degrees and is much higher than that of Sodium (A=23,) which is 98 degrees. It is however, related to the molecular mass. The heavier a molecule is, the higher its melting point. For example, the melting point of methane is 182 degrees, whilst the melting point for hydrogen fluoride is 83 degrees. This rise with increasing molecular mass is due to the increase in intermolecular forces, namely dispersion forces, which are weakly attracting.
What is the melting point of NaCl?
(Meredith Blackmore)
Sodium chloride (commonly called table salt) has a melting point of 801C.
How do you measure Density using Archimedes Method?
(Carol Jackson)
The volume of an object can be measured by placing it into a known volume of water. The volume of water that is displaced by the object exactly equals the volume of the object. Next, the mass of the object is accurately measured. The density if the object is obtained by dividing the mass of the object by ita volume. This is the Archimedes principle.
How could you experimentally determine that the gas produced when an alkali metal reacts with water is hydrogen?
(M Hayward)
If you can safely trap the gas that is produced, it can be tested with a lit splint (or string.) Place the flame near the opening of the container and release the gas slowly. If a popping sound is heard, the gas is hydrogen. If the flame dies out, the gas is carbon dioxide, and if it burns larger, the gas is oxygen.
I would like to know the boiling point of tri-isopropylbenzene.
(Nadzarudin Latif)
232 236C, and this was obtained from a Material Safety Data Sheet (MSDS)
Could you tell us please whether glycogen is soluble or insoluble.
Is there is a way to separate dry ice into carbon and oxide?
How do I recover silver from the negatives of pictures after development?
Please explain the effects of different contaminants on the growth rate of rust.
I would like some assistance on an experiment regarding batteries (See answer for detailed question)
What is the process by which the biopolymer glucose is formed?
What are the optimum conditions for formation of Chromium VI?
I want to ask if there is isomerism in C2H5(CH3)C=CHCH3? Please explain.
Why does Hg have a smaller radius than Cd when Hg has more occupied energy levels?
Why do most ionic substances dissolve whereas few covalent substances dissolve?
What is a brief way to explain the chemistry of smell? How are smells distinguished and perceived?
What is the scientific principal or scientific discovery behind Luminol? How is Luminol made?
Can you give me some information about the ester butyl ethanoate?
Can you provide some information on the pros and cons of artificial sweeteners?
A neutron can decompose into a proton and an electron. I have a few questions on this topic please.
How do you stabilise methyl salicylate in formulations containing thymol, ethanol and benzoic acid?
I'd like to ask my own question. |
I'd like to ask my own question. |
Could you account for me the shape of pH curves. I understand that pH=-log(H ions). Could you explain the shape of the curve and relate it to kinetics?
(D.Longfellow)
This specialist question requires a very detailed answer. Go to this link for details
When preparing esters one needs to reflux the reagents over a period of time in the presence of a catalyst. Could you specifically tell me when does one use a water bath in the process rather than a open bunsen flame. I understand that compounds of a low molecular weight have low boiling points.
(D.Longfellow)
There are many ways to synthesise esters, all involving different substrates and reaction procedures. I am presuming the questioner means that they are intending to synthesise the ester from a carboxylic acid, a substantial excess of the alcohol and a strong acid catalyst.
The choice of steam bath, bunsen, or indeed oil bath, heating mantle or some other heat source, is really only one of practicality. It has to be able to reach a temperature sufficient for the mixture to boil. This will vary from one example to another. If, for example, one was making a methyl ester using an excess of methanol, a steam bath would be sufficient as the boiling point of methanol (the solvent as well as the reactant) is 65. If one was using a similar proceedure to make the 1-octyl ester (and there are probably better methods in this case), one would need hotter reaction conditions since the boiling point of 1-octanol is 157.
Could you tell us please whether glycogen is soluble or insoluble. We understand that amylose is soluble whereas amylopectins are insoluble due to their hightly branched nature. We understand that Glucogen has a still more highly branched structure than amylopectins yet we found information stating that was soluble. Please explain.
(D.Longfellow)
The starch story is complicated. Amylose, once isolated from the starch granules, undergoes a process known as retrogradation, in which the linear amylose molecules coalesce - the product has low solubility. The branched amylopectin molecules are more soluble than the retrograded amylose molecules. Glycogen, also a branched molecule, is also soluble. There is a voluminous literature on starch and the enquirer is referred to the nearest library for information.
Is there is a way to separate dry ice into carbon and oxide?
Full Version of Question:- Ok I don't know what area of chemistry this belongs to but anyway. I'm trying to invent something here but It's giving me a hard time because this can be a big thing but it's kind of complicated. All I need to know is if there is a way to separate Dry ice into Carbon and Oxide.
No. (Simple answer).
Longer answer. No - because:
A bit of thermodynamics - When you burn carbon in oxygen you get a molecule called carbon dioxide which looks a bit like OCO . (Note that the word 'oxide' indicates oxygen in combination with another element). Lots of heat is given off (this is what happens when you burn coal), because the carbon dioxide molecule is much more stable than the carbon and oxygen you start with. This difference in energy has to go somewhere and it is given off as heat. It follows that if we wanted to reverse this reaction we would have to put in this large amount of energy.
This is only the first problem (having to supply lots of energy). It turns out that practically we cannot do it simply by heating up carbon dioxide - the molecule is simply too stable. In fact there is no way that we can go back to carbon and oxygen directly. Nature does a clever trick in plants to convert carbon dioxide and water into glucose (a sugar compound of carbon, hydrogen and oxygen) and oxygen but we have not managed to reproduce this photosynthesis in the lab.
Is there a way to contain carbon in the solid form while letting the oxygen off as a gas directly from dry ice?
Full Version of Question:- I need to know if there is a way to contain carbon in the solid form while letting the oxygen off as a gas directly from the dry ice. It is important that the Carbon is not let off when the gas is let off from the dry ice. Is there any mixture of chemicals that might do something to this effect? Or maybe to cancel the carbon in the dry ice but still contain it's coldness. As you can see I'm trying to eliminate Carbon from dry ice and keeping the area around the dry ice freezing cold.
A way to get carbon back is to react the carbon dioxide with a substance that has a greater affinity for the oxygen than carbon. If you take a piece of burning magnesium ribbon (DANGER! do not do this without safety precaustions and training) and enclose it completey in solid carbon dioxide, it keeps on burning. Now the magnesium takes the oxygen from the carbon dioxide leaving black carbon and white magnesium oxide behind. The chemical equation for this is CO2 + 2 Mg --> C + 2 MgO.
After development of the pictures from the negative in photography some waste water remains which has some silver in it. I have tried to dissociate its silver with ( 1- HCl then 2- NaOH then 3-HNO3 & then adding Formaldehyde ) but it was not a good way. Please tell me how I can get its silver by a high degree of quality cheaply. (It is better to say that the waste water is red and it is used in color photography and it is from a milk company.)
(Youness Ansari)
Youness, there is a number of options from iron substitution to electrodeposition but these are well dealt with on a particular web page. Enviroscience has an article (62 pages) entitled " Guides to Pollution Prevention The Photoprocessing Industry". This has a web address as follows: http://es.epa.gov.program/epaorgs/ord/photoind.html. This document deals with the recovery from developer, fixer, scrap etc and is well detailed in its chemistry and very descriptive in dealing with the subject the options of recovery and goes on to include the levels of silver on films, economics etc. On the other hand, Murdoch University, Department of Chemistry have this subject as a topic "No; 26 Silver Recovery" and have many further references to the data including reference to Kirk-Othmer Encyclopedia.
I am doing a project on the effects of different contaminants on the growth rate of rust. I have jars with different contaminants and then a nail is placed in it. I was wondering if the amount of the substances in each jar will affect the outcome of my experiment? Also, does the amount of air exposed to the nail affect how long it takes to rust? My experiment is only for five days, is that enough time for it to rust?
(Katrina)
Dear Experimentalist,
I should firstly admit that I'm not a great expert on rust, but I'll do my best to answer your questions. There are many factors to consider in this experiment, so if you want to carefully test each contaminant you must be sure that everything else is the same in each jar.
* Surface area of the nail: It would be a good idea to use some emery paper to scratch the surface of each nail. This will also help to remove any oils/grease from the surface, which would inhibit rusting. You might also want to wash each nail in detergent, being careful not to touch it with your fingers after doing this.
* Type of nail: for good reasons, many nails are designed to be highly resistant to rust. Make sure you don't use galvanised ones!
Depending on what your contaminants are, I would imagine that the most important thing will be how "salty" the solutions are - e.g. household salt and any other contaminants that dissolve to form ions will speed up corrosion. And, YES, the amount of air exposed to the nail does affect how long it will take to rust. Corrosion is an oxidation process, that is, it uses the oxygen out of the air for the process to occur. The more contact with air, the more corrosion expected.
The length of time for your experiment will depend on what nails you are using and on how you choose to measure the amount of rust on each nail - the easiest way, of course, is just to look at the nail, in which case I'd imagine 5 days should be long enough to see the beginnings.
Finally, if you discover anything to add to your solutions that greatly inhibit rusting, make sure you take out a patent!
What functional groups are present, what type of bonds are between atoms, and what is the molecular geometry around the central atoms in Isoflurane?
(Angela Rasch)
Isoflurone is 1-chloro-2,2,2-trifluoroethyl difluoromethyl ether. It therefore contains the alkyl halide (fluoride) and ether functional groups. It contains C-C, C-H, C-O-C, C-F bonds. Th molecular geometry around the central atoms, which I take to be the ether part, is essentially tetrahedral, if you include the two lone pairs of electrons on oxygen. In other words, there would be a C-O-C bond angle of about 112.
Can you give me some information regarding 'the chemical reaction kinetics'of the reaction between salicylic acid and acetic anhydride with toluene as a solvent to produce aspirin and acetic acid?
(Sushil Mathakri)
In thinking about the kinetics, write down the overall equation and consider the mechanism of the reaction. Next, think of the reaction profile, that is, the energy of the system as a function of the progress of the reaction. Thermodynamics depends upon the energies of the reactants compared to the energy of the products, and can be energy releasing (exothermic), energy absorbing (endothermic) or with no energy release or absorption (thermoneutral). Kinetics on the other hand involves processes at the boundary between reactants and products (the transition state). It depends for example on the number of species that must collide to give the transition state.
Kinetics refers to the rate (R) (or speed) at which a reaction takes place. If a reaction involves only one species in its transition state then:
R is proportional to [concentration of reactant]
If the reaction involves three species in its transition state then:
R is proportional to [concentration of reactant 1]x[concentration of reactant 2]x[concentration of reactant 3]
What is the advantage of using toluene as a solvent for industrial manufacture of acetyl salicylic acid(aspirin) ?
(Sushil Mathakri)
Reactions are driven forward by removal of products or side products. Hence, perhaps toluene can remove the side product. Does it form an azeotrope with toluene?
I am doing a science experiment over batteries and I was wondering if you could help me. My experiment poses the question, "Does a battery last longer if it is left on continuously or if it is turned on and off periodically (every hour)?". And of course only the ""on"" hours for the off and on battery is accounted for. After 24 trials, I have concluded that leaving the battery on continuously lasts longer by approximately 9 or 10 %. However, I don't know the explanation for my conclusion. I am leaning to think that when a battery is turned off, you lose power to the load, and I think that the chemical reaction is still occurring in the battery as the reaction comes down to a stop which is a waste of chemical energy because nothing is turned on. And I think that it takes a higher magnitude of chemical reaction to get it back started again. I would appreciate it if you would give me your perception and your explanation. Could you also please write your explanation in scientific terms, because I really need to know this in detail so I may be able to understand and expand on my project.
(David Poarch)
It is difficult to answer this question without knowing what type of battery the student is referring to, but assuming that David is referring tothe standard alkaline batteries, then, the answer can be quite complicated depending on how the battery is being discharged (ie at what current) and even what brand of battery it is. Different brands of batteries are designed to deliver the most energy under high discharge rates, while others under low discharge rates. Normally, you would expect that when you intermittently use the battery, you should get more energy out of it because the solid state reactants have a chance to rearrange themselves so that they can access the electrolyte solution to continue the reaction. That is why when you are running your video camera or other portable appliance, it might cut out when the battery goes flat, but if you let it rest for a few minutes and switch it back on again, you can usually get a few more minutes of life from them before they cut out again. The fact that the student has observed a 9-10% increase with continued use, could be due to variation from one battery unit to another. He would need to test up to 10 batteries under each condition and average the results for each set of batteries to get a more statistically significant result. Without further information, I can really only speculate on the cause, but hopefully, the above comments might be of some use.
What is the process by which the biopolymer glucose is formed?
(Anthony Carney)
Glucose itself is not a biopolymer, rather it is a small biomolecule (monomer) which can be built into a variety of biopolymers. Glucose itself is formed (along with a number of other sugars) in plants as a result of photosynthesis. It may then be converted to starch by a system of enzymes. Starch is a storage biopolymer, and is the main source of carbohydrate in the human diet. Cereal grains such as wheat, corn and rice are high in starch, which is the principal energy storage material used by plants. Glucose is also converted by other enzymes to cellulose, which is a structural biopolymer. Cellulose is the principal component of most plant cell walls, and is the most abundant organic polymer on earth. Other biopolymers in close association with cellulose form a structure able to support the growth of enormous trees. Cellulose is a major component of timber.
We sell Coffee OiL derived from the roasting of coffee beans. The Oil is sold as a flavor enhancer. One potential buyer asked the following question; "Since our coffee Oil is at 77 Brix, what is the cutting ratio of a 2 ounce sample to bring the Brix to 9?" How can this be determined and what is the formula for doing so, in laymens terms please.
(Richard Della)
Brix (measured with a refractometer) is an unusual way to measure the concentration of an oil. Usually refractive index is used. Brix is an alternative scale in a refractometer used specifically for sucrose solutions. So 77 Brix is the reading for a 77% solution of sucrose in water. It is sometimes used for other sweeteners (eg liquid glucose, honey) but the actual concentration would vary slightly from the Brix reading. So, as Brix is a concentration measurement to dilute 77 Brix to 9 Brix would require a dilution of about 8.5 times. The problem is what would you dilute it with. I am guessing the coffee OIL is used as a flavour in a food product such as a syrup, cream, ice cream, cakes. I would use ethanol.
I am researching Chromium (VI) compounds. I have been able to find plenty of literature about sources, environmental and health effects. What are the optimum conditions for formation of Chromium VI?
(Leah Kelly)
Chromium(VI) and Cr(III) are the most common oxidation states of chromium. In nature Cr commonly exists as Cr(III) (generally as chromite). Some Cr(VI) minerals exist, eg crocoite but these are relatively rare. Cr(VI) complexes exhibit a similar geometry to phosphate and sulfate anions. It is this property that is believed to be the reason for the rapid uptake of Cr(VI) into cells. Cr(VI) is also a strong oxidant which causes damage in vivo that leads to its carcinogenic properties. A lot of attention was focussed on environmental Cr(VI) exposure in recent years following the incident in Hinkley, California (the subject of the movie Erin Brokovich), whereby a number of townspeople were exposed to Cr(VI) from contaminated drinking and irrigation water and consequently developed health problems including cancer. This Cr(VI) exposure resulted from industrial pollution. Generally, strong oxidising conditions, that are not commonly encountered in nature, are required to produce Cr(VI). The industrial method for producing Cr(VI) occurs by treatment of chromite (generally containing Cr(III) as FeCr2O4) with molten alkali and oxygen. Another method involves the digestion of a Cr compound in a highly acidic oxidising medium such as concentrated HNO3 to form aqueous Cr(VI). This latter method is commonly used for preparation of samples for quantitative Cr analysis.
I was wondering how could one tell if something such as carbon tetrachloride is soluble in water? Both components, the carbon tetrachloride and water are colorless, so when you mix them together, how can you distinguish between immiscibility or solubility?
(Al)
Let's look at definitions of soluble and miscible. Solubility is the maximum quantity of one phase dissolved by another under specified conditions. Substances are generally soluble in like solvents. For example, organic molecules are soluble in molecular solvents such as CCl4, ethanol and ether, while inorganic salts are often soluble in water, and less soluble in organic solvents. Miscibility, however, denotes the extent of mixing. Gases mix in all proportions and are said to be completely miscible. Liquids may be completely miscible, partially miscible, or almost completely immiscible. The miscibility of liquids depends upon their chemical and physical similarities, and in particular on their internal pressures. Liquids which have approximately equal internal pressures are miscible in all proportions.
So with your example of carbon tetrachloride in water, using the above information, the carbon tetrachloride is insoluble and almost completely immiscible in water. After mixing and allowing to settle, although both are colourless, there are two distinct layers visible.
I want to ask if there is an isomerism in C2H5(CH3)C=CHCH3? Please explain
(Abrar)
Isomerism is where compounds possess the same composition and the same molecular weight, but differ in the chemical structure. Each structure is called an isomer, and isomers have differing physical and physiological properties. So, with your example, there are no isomers for this compound as all carbon bonds are full and cannot be turned on an axis or configured in a different way as written to give an isomer.
What factors affect the intensity, duration, and efficiency of chemiluminescence? Could you also provide any other information you have on chemiluminescence?
(Jon)
Chemiluminescence occurs when a chemical reaction yields an electronically excited species that emits light as it returns to the ground state. Another way of thinking of this is that light is one of the products of a chemical reaction. Therefore, the factors that dictate how rapidly and how long a chemical reaction occurs apply to chemiluminescent reactions. Therefore a chemiluminescent reaction will occur until one of the reactants is entirely consumed. The intensity of the light emitted is dependent on the rate of the reaction and the chemiluminescent quantum yield. The quantum yield is the number of photons emitted per molecule reacted and is typically between 0.01 and 0.2.
A classic example of a chemiluminescent reaction we are all aware of
is the green light produced by light sticks and necklaces you seem to always
be able to buy at fairs and shows. These light sticks contain Luminol which
reacts with hydrogen peroxide and some weak base. In some cases the light
sticks have a little glass ampule containing the hydrogen peroxide. Upon
bending the light stick the ampule breaks, the hydrogen peroxide is released
and the light stick glows. The stick continues to glow until all of one
of the reactants is consumed. One common way to slow this reaction down
in to put the light stick in the freezer (the way your fairground seller
keeps the necklaces). The light stick also goes a much darker, less intense
green colour as the reaction rate is slowed down. This demonstrates the
role the reaction kinietics in determining the duration and intensity of
a chemiluminescent reaction.
Why does Hg have a smaller radius than Cd when Hg has more occupied energy levels?
(K Guglielmo)
The size of an atom is, for practical purposes, defined as the boundary surface inside which the outermost (valence) electrons are to be found 90% of the time. The radius (i.e. size) of the valence orbital is governed by a balance between two opposing forces: (1) The mutual repulsion between electrons in the valence orbital, and between valence electrons and 'core' electrons (electrons in closed shells closer to the nucleus) (this repulsion by core electrons is known as 'screening' or 'shielding'), and (2) the attraction of the valence electrons to the protons in the nucleus. Cds and Hg are in the same group of the periodic table, so the valence electron configuration is similar. Their big difference is their nuclear charges (Z=80 for Hg and Z=48 for Cd). One might expect the 80 protons in the Hg nucleus to attract the valence electrons stronger than the 48 protons of Cd, and this point, alone, might be used to explain the size difference - but the full story is more complicated: The electrons that counterbalance the nuclear charge usually almost exactly offset the increased nuclear attraction - which explains why atoms do not get uniformly smaller with increased nuclear charge. The important factor in your example is that, for Hg, the most recently added electrons ( just below the valence electrons) are electrons in 'f' and 'd' orbitals. Electrons in these particular types of orbitals are poorer at screening valence electrons from nuclear charge, so the valence electrons of Hg are pulled in close, so Hg is smaller than Cd (which has many fewer 'd' electrons and no 'f' electrons). The affect of the 'f' electrons of the lanthanides (located between La and Hf) upon atom sizes is so pronounced that it has been labelled the 'lanthanide contraction'. (You can use this as a search term on the Internet or in textbook indices). Thus, like the Cd/Hg comparison, Zr and Hf are almost identical in size (and therefore chemistry) even though one would expect Hf to be bigger, owing to the naturally bigger valence orbital. All across the transition metal series, the lower two elements of each triad are similar in size and chemistry, and both differ considerable from the first member.
Why do most ionic substances dissolve whereas few covalent substances dissolve?
(Carol Simons)
First of all, I am going to assume you mean 'dissolve in water' - because this assumption affects the reply. It is not necessarily true that most ionic substances dissolve. There are many oxides and fluorides of divalent and trivalent metal ions that are very poorly soluble. The reasons for something being soluble are complicated, but essentially a substance will dissolve if it is, overall, more energetically stable in solution. (This DOES NOT necessarily mean that heat must be evolved - I am talking about 'Gibbs free energy' - a type of total energy that includes heat and other energy forms that I think are not discussed in High School chemistry). Similarly, it is not necessarily true that few covalent compounds dissolve. You could count the myriad of possible sugars, polysaccharides, proteins etc. as covalent, but they are often quite soluble. When you try to dissolve something made of covalent molecules in water, it costs energy to break the forces between the molecules, and it costs energy to break the bonds *between* water molecules (special bonds called 'hydrogen-bonds') when the covalent molecule is inserted between the water molecules (i.e. 'dissolves'). If the inserted molecule can form bonds of similar number and strength to its neighbouring water molecules, as were broken as described above, then the energy costs will be off-set by the energy gain, and the substance is likely to be soluble. If not, then it will probably be poorly soluble. When an ionic substance dissolves, the ions become more separated in space, and it costs energy to separate a cation from an anion (work is done against Coulombic attraction - physics). When the ions are put into water, energy is released when each cation and anion forms strong bonds to the electric dipoles of water molecules - called 'solvation energy'. There is an additional entropy component, but you may not have studied that. Thus, an ionic substance will dissolve if the total energy (Gibbs free energy) is favourable - this consisting of a combination of these favourable and unfavourable energy terms.
Do you know in general what the combustion products of a solvent-based detergent cleaner would be? Are they harmful? Do you know what the general combustion products of a water based cleaner would be? The reason I ask is because I am doing a project on the running wash of gas turbine compressors.
(Chris Hay)
Do you know in general what the combustion products of a solvent-based detergent cleaner would be? These products could really be anything but many solvent based cleaners are totally volatile. For example one could be based on butylene glycol, lemon oil and isopropanol leaving no residues and relatively innocuous combustion products. There are others which do contain complex organic compounds cut in solvent and again many of these leave little or no residue so it is very hard to surmise what the combustion products may be apart from water and carbon dioxide unless one is fully conversant with the ingredients used in the particular compound.
Are they harmful? Usually not, but the solvent system or the active organic cleaners could be more harmful than the combustion products, this information is nominated by suppliers in their Material Safety Data Sheets (MSDS's).
Do you know what the general combustion products of a water based cleaner would be? Again there is such a vast number of options available for cleaners with some based on detergents such as Sodium Dodecyl Benzene Sulfonate or Sodium Sulfo-Succinate or Glycollated Esters etc etc. There is a vast range of active ingredients some with Anionic base some Cationic and still more which are classified as non-ionic and many of these may be involved in water based products either singularly or as blends. The ester surfactants locally are supplied by people such as Huntsman Australia and the formulators using such as these have such a vast array of systems available that it would be very difficult to guess on the fomulae in use as these will vary significantly from different proprietery brands.
The reason I ask is because I am doing a project on the running wash of gas turbine compressors. We would suggest that the technical people, possibly the Environmental Manager, at Qantas Air Base may be prepared to give you some of the information that you are seeking as 1) they will have an approved product for use on turbines and 2) they will be obliged to be holding the relevant MSDS to ensure Occupational Health and Safety requirements.
What is a brief way to explain the chemistry of smell? How are smells distinguished and perceived?
(Angie Junge)
Airborne molecules (odorants) are captured by large protein molecules (receptors) imbedded in the membranes of nerve cells in the noes. Their capture is registered as a chemical cascade inside the cell, which generates a nerve impulse. Different parts of the airborne molecule are the points of capture by different receptors. A number of different impulses are therefore generated for each type of odorant, forming a neural code analogous to your bank pin number. Your brain then interprets (possibly after repeated exposure to the same source of odour) that this neural code is the experience of the odour of that object or odour source. The names of odours invariably involve the name of the odour source, such as "rose, "lemon", "burnt rubber", "sweaty socks", etc. The brain has over 10 billion nerve cells, all highly interconnected, and this capacity for information processing allows it to form a unified identity for objects which in the real world actually give off hundreds of single smelly compounds. The smell of a rose is therefore analogous to the chord on a piano rather than the sound of a single note. Smell information is conveyed to several parts of the brain where presumably it takes part in forming memories and impressions of the space we live in. Psychologists have recently shown that experience of odours affects our judgement of their strength and impressions of liking or disliking them: unfamiliar odours are experienced as weaker and are less liked. So in this way smells are perceived (transformed from physical information into a complex human experience by the complex human brain) and distinguished (differentiated from one another by attribution of an identity, which in the case of a complex odour mixture, can be reduced to a very complex neural code).
What is the scientific principal or scientific discovery behind Luminol? How is Luminol made (if someone wanted to start a business to manufacture it)?
(Kristin Bautista)
The chemical name for Luminol is 5-aminophthalhydrazide. Luminol is a yellow crystal, with a melting point of 329 - 332C. Treatment of this material with a number of oxidising agents in the presence of alkali causes it to emit a blue light (chemiluminescence). Luminol is prepared using 3-nitrophthalic acid. References where you will find the detail are:
Huntress et al., J. Am. Chem. Soc. 56, 241 (1934),
Redemann, Redemann, Org. Syn. 29, 78, 8 (1949)
L. Fieser, Organic Experiments (Boston, 1964) pp 240 - 242
Can you give me some information about the ester butyl ethanoate? eg: uses, properties, structure and how would I prepare it using the alcohol and the acid.
(Aimee)
There are 3 esters corresponding to the corresponding 3 butanols, namely:
Normal butyl ethanoate, with a boiling point of 126C
Isobutyl ethanoate, with a boiling point of 118C
Secondary butyl ethanoate, with a boiling point of 112-113C
They are colourless liquids with fruity odours and are important solvents for cellulose lacquers. References for the preparation are:
Leyes, Othmer, Ind. Eng. Chem. 37, 968 (1945)
Vogel, J. Chem. Soc. 1948, 624
Zettlemoyer et al., U.S. pat. 2, 644-839 (1953 to FMC)
Can you provide some information regarding the pros and cons of artificial sweeteners?
(Steve)
Our suggestion for you is to look up the appropriate Material Safety Data Sheet (MSDS). These are all electronically available from the UNSW web site, found at:
UNSW.CHEM.UNSW.EDU.AU/LOCAL
Select the SAFETY heading, then select SIRI MSDS. From here, type in the word SACCHARIN to search for the MSDS you are looking for.
A neutron can decompose into a proton and an electron. So does that means that the combined mass of a proton and an electron is equal to the mass of a neutron? Hence, does that mean a neutron is heavier than a proton? So why does a proton decompose into a neutron and a positron? That would have to mean that the combined mass of a positron and a neutron is equivalent to the mass of a proton, and that the proton is heavier than a neutron. That contradicts what I stated before. Why is that so?
(Ben Chea)
The question is physics, not really what we bother about in chemistry. A physicist would give you a far better answer - but the following may bet you started: The problem may be caused by using quoted 'at-rest' masses in the calculations. In real decays, the separating particles often diverge with kinetic energy (and consequesnt velocities) which may add a relativistic modifier to their masses. Indeed, decays often involve the partial conversion of mass into energy (E = mc^2), and this consideration (alone) may account for the disagreement in the mass sums.
I want ask about procedures of esterification of acetic acid and ethanol with catalyst of sulphuric acid
(Sisca Verawati)
Esterification of acetic acid and ethanol in the presence of a catalytic
amount of sulphuric acid can be performed in a number of ways, the most
common is to dissolve the acetic acid and ethanol in a non polar solvent
such as toluene, add a few drops of sulphuric acid and heat the mixture
at reflux. After completion, pour the mixture into water and separate the
organic layer (product, toluene) the sulphuric acid, unreacted acetic acid
and unreacted ethanol should be in the water layer. Distillation of the
organic layer will give two products 1. ethyl acetate (product from esterification)
60 degrees. 2. toluene (solvent) 110 degrees.
How can I get boric acid into a liquid form at room temperature? Ideally I need a liquid formula of 10% boric acid in water and sugar.
(Scott Waddell)
Boric acid is soluble to the extent of about 5.5% in cold water (1g dissolves in 18 ml cold water). The solubility can be improved by heating the water (1g will dissolve in about 4ml boiling water). The Merck Index also suggests that the solubility is increased by the presence of citric or tartaric acid so maybe the sugar will help. I suggest making up a sugar solution first (100ml) and then try to dissolve 10g boric acid in that solution, use some heating if necessary.
How do you stabilise methyl salicylate in formulations containing thymol, ethanol and benzoic acid?
(Sunil Sarmalkar)
We do not have sufficient information to respond to this question as methods of stabilisation will depend on whether the formulation is that of a tablet, liquid or some other form.
How can you tell sodium carbonate apart from sodium bicarbonate if you only have Phenolphthalein, Isopropyl alcohol, Iodine, Acetic Acid, Water, and CuSO4?
(Edwin Rodriguez)
Prepare an aquaeous solution of the salt, and a solution of Phenolphthalein in Isopropyl alcohol. Add a few drops of the Phenolphthalein solution to the salt solution. If the colour turns purple, you will have sodium carbonate. If the solution remains colourless, you will have sodium bicarbonate.
Synthetic Gypsum (CaSO4.2H2O) produced as a by-product of industrial acid gas scrubbing is a black sludge and presents a significant waste disposal problem. I understand that it can be refined in some way and used to make wall board and other gypsum and plaster products. What are the processing steps to refine it? Also can the Calcium-Sulfate bond be broken and the Ca & S components recycled or can another useful by-product be produced from it, such as ammonium or sodium sulfate? These solutions should have a significant positive environmental impact.
(Bill Spencer)
This question can be only answered with other questions, particularly in relation to what may be composition of the black sludge. By way of explanation, the black may be "heavy metal compounds" or carbon deposits, one relatively harmless and the other which could be toxic and hazardous depending on the metal and other species present, which could include arsenic compounds. It would need a thorough understanding of the process to speculate on the "clean up" processes required.
In answer to your question , I am convinced that the basic building blocks, Calcium Ions and Sulfate Ions can be manipulated such that they can be combined or recombined to be used in gypsum or plaster products. The concept of conversion to alternatives such as ammonium or sodium salts has its merits but one needs to look carefully to a balance, a balance to examine the costs to the environment of the different solutions. It may well be that too much focus on the by-products could cause more environmental damage / problems than a basic or simplistic processing of the wastes. I realise that this does not provide the simple answer that you were hoping for, but the many possible answers and sub-challenges in your question make a straight forward answer impossible without much more data regarding the products being scrubbed in the first place.
What is the chemical equation for the production of ethanol from fermentation? How is ethanol used to produce alternative fuels to gasoline and is it practical in replacing gasoline in the future?
(Crystal)
There is no single equation for the fermentation of ethanol, it proceeds from 3 basic starting materials, sugars (molasses), starchy substances and cellulose-containing substances. Each with its own pathway which are also set by the action of four enzymes, diastase, maltase, zymase and invertase.
In essence these systems are:-
(a) From cane sugar molasses (sucrose)
invertase
C12H22O11 + H2O -----¶ C6H12O6 + C6H12O6
Sucrose glucose fructose
This is then converted to ethanol by zymase
zymase
C6H12O6 ----¶ 2C2H5.OH + CO2
(b) From starchy substances (potatoes)
Boil with
(C6H10O5)n + nH2O ----¶ nC6H12O6
starch dilute acids glucose
Excess acid is neutralised before further treatment
Or crushed malt is added and reaction proceeds as;
diastase
2(C6H10O5)n +H20 ----¶ nC12H22O11
starch maltose
Both the above convert to alcohol as in (a).
Or using a mould as the source of enzyme (In the EU particularly tis is known as mucor being the source of diastase).
maltase zymase
C12H22O11 + H2O ¶ 2C6H12O6 ¶ 4C2H5.OH + 4CO2
Maltose glucose
(c) Manufacture from cellulose (wood, sawdust, straw, grasses)
This reaction is facilitated by heating with dilute mineral acids under pressure:
(C6H10O5)n + nH2O ¶ nC6H12O6
cellulose glucose
This also then converts after neutralisation as in (a) and (b).
Ethanol is currently used as a fuel supplement or extender, if you like whereby it is added to a gasoline type product and sold commonly as "Gasahol" or added to a diesoline product and sold as "Diesahol". In both cases it is sold as a mixture rather than a raw fuel in its own right, it can be used but it is a poor fuel by itself and has the added problem of water absorption with corrosion as well as combustion problems. As an extender however, it is most useful and can be brought to an acceptable price as it is currently. Some countries (particularly under-developed) already have the blend as their primary transport fuel.
Is there a simple method to analyse the phosphate content of detergent and the nitrogen content of fertiliser. I need to perform these analytical experiments in a standard school laboratory.
(Luke Hanson)
1. Nitrogen in Fertiliser.
A good reference is the AOAC Official Methods of Analysis. Two methods for total nitrogen determination in fertilisers are reported.
A. Combustion Method (AOAC Official Method 993.13)
B. Kjeldahl Method (AOAC Official Method 955.04)
However, neither of these are particularly suitable to the school laboratory as they both require the use of hazardous concentrated acids and specialised
steam distillation apparatus. The following method was found in Conquering Chemistry (most recent edition) p213, and may be more appropriate to your needs. It discusses the determination of the ammonium ion concentration in fertiliser. This involves the addition of a known amount of sodium hydroxide to the fertiliser sample and heating to drive off all the ammonia. The excess hydroxide is then titrated with standardised hydrochloric acid to back calculate the amount of hydroxide consumed in the reaction. The ammonium concentration can then be calculated and the total nitrogen predicted if it is assumed that all nitrogen is present as ammonium.
2. Phosphate in Detergents
The following was again obtained from Conquering Chemistry and it is in the form of a problem. 6.92 g of laundry washing powder was dissolved in 500 mL of water. A slight excess of a solution of magnesium chloride in an ammonia/ammonium chloride buffer was added to this with stirring until precipitation was complete. The precipitate was filtered and dried. The mass of the precipitate was found to be 1.83 g. It is assumed that the precipitate is pure magnesium ammonium phosphate hexahydrate. (Mg(NH4)PO4.6H2O)
I would like to know a way that I can experimentally find the percent mass of sodium bicarbonate in an AlkaSeltzer tablet.
(Kylene)
The short answer is that our resident expert, after considerable time in the lab, as been completely defeated. However, we emailed the manufacturers of AlkaSeltzer, and have received the following response:
We do the experiment to determine the sodium hydrogen carbonate in Alka-seltzer as part of our study of gas laws. Thus our focus is more on the use of gas laws and chemical stoichiometry. We react a weighed Alka-seltzer tablet with excess hydrochloric acid, HCl, to produce carbon dioxide gas, CO2. We collect the carbon dioxide while displacing water from a flask, so that we determine the volume of carbon dioxide gas produced. Determining also the temperature and pressure of the carbon dioxide gas, some small corrections are required, we are then able to use the ideal gas law to determine the number of moles of carbon dioxide gas, and thus using the balanced reaction between sodium hydrogen carbonate and hydrochloric acid to produce carbon dioxide gas, we stoichiometrically calculate the moles of sodium hydrogen carbonate and hence the mass of sodium hydrogen carbonate that was present in the tablet. The results are surprisingly good, in that many students get results within a few percent of the value listed on the manufacturers label.
If you need to simplify, I think it could be possible for students to just measure the volume of water displaced as equal to the volume of carbon dioxide produced from the sodium hydrogen carbonate. If you do the stoichiometry using typical ambient experimental conditions, the students could simply be told that a given volume of carbon dioxide gas relates to a given mass of sodium hydrogen carbonate under typical conditions for their experiment.
Also, the world wide web (www) turned up a site that may be if use for you:
(http//1pc1.clpccd.cc.ca.us/pc/deleray/1aa99.htm)
which lists a practical time for the determination of sodium hydrogen carbonate
in Alka-seltzer, but no detail.
I'd like to ask my own question. |
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Last Revised: 14th March 2002