24 Carat Chemistry

I was trying to buy a present for my mum for Mothers' Day. "A gold chain," I thought, "would be a nice present". But when I got to the jewellery shop I found that there is a huge variety of "gold chains", 24 carat gold, 18 carat gold, 9 carat gold, 995, 750, 375, white gold, rose gold...

So what is a carat?
What do those numbers mean?
How can "gold" be different colours?

Read all about it in the June 2019 issue of AUS-e-NEWS

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Nanocellulose Foam

You have probably held polystyrene cups (styrofoam cups) in your hands. It is a wonderful material for making disposable cups because it is light-weight, holds it shape well, and is an excellent insulator. All this means that you can fill a polystyrene cup with hot tea and drink from it without having it burn your hands. High school chemistry teachers are very fond of using polystyrene cups as "cup calorimeters" in the school laboratory. Unfortunately, polystyrene is not an environmentally friendly polymer, it doesn't break down, it is chemically inert, so persists in the environment.
Plant-based polymers which degrade in time, such as cellulose, could replace polystyrene if we can make a cellulose-based material with same properties as polystyrene.
Cellulose is a polysaccharide. It is composed of many glucose units joined together by ether bonds (glycosidic links). During acid hydrolysis these ether bonds (glycosidic links) are attacked and broken so that the final product of a complete reaction is a lot of glucose molecules. The reaction mechanism for the acid hydrolysis of cellulose is shown below:


If only some of the ether bonds (glycosidic links) within a cellulose polymer chain are attacked, then you could end up with shorter chains of glucose polymer, still enough glucose units in the chain to be considered cellulose. If these chains are only 5-20 nanometres wide (even though they may be several micrometres long) they will be referred to as nanocellulose.
Researchers at Washington State University have added polyvinyl alcohol, shown below:

to nanocellulose. Polyvinyl alcohol binds to the nanocellulose which stabilises the foam that can be  produced. This light-weight material is reported to be a better insulator than polystyrene foam (styrofoam) and "can support up to 200 times its weight without changing shape. It degrades well, and burning it doesn't produce polluting ash."

Suggested Further Reading:
Nanotechnology

Suggested Study Questions:

1. Convert the following measurements to metres (m):
   • 5 nm
   • 20 nm
   • 100 μm
   • 1000 μm
2.  Convert the following measurements to nanometres (nm)
   • 5 × 10^-9 m
   • 2.5 μm
   • 5.2 mm
   • 0.75 cm
3. Draw a section of cellulose polymer containing 6 glucose units. Circle the ether bonds (glycosidic links) in red.
4. Draw the results of acid hydrolysis if all the ether bonds (glycosidic links) in this section of cellulose polymer were broken.
5. Draw the results of acid hydrolysis on the section of cellulose polymer you drew for question 3 if only 2 new "molecules" are produced. Is there only one possible answer? If more than one answer is possible, how many possible answers can you think of?
6. Consider the structure of cellulose and of polyvinyl alcohol. Explain how polyvinyl alcohol can "bind with" cellulose. 
7. Explain why a nanocellulose foam can be stabilised by adding polyvinyl alcohol.
8. Consider the combustion of cellulose. Give the products for
   • complete combustion of cellulose
   • incomplete combustion of cellulose
9. Wood is composed largely of cellulose. When a wood log burns on a camp fire it produces a sooty flame. Explain why.
10. Explain why nanocellulose is unlikely to produce a sooty flame when it burns.

Breaking Triglycerides up into Fatty Acids

Triglycerides are found in the fats and oils you eat. They are produced in a condensation reaction between a glycerol and 3 fatty acids. So, is it possible to reverse this reaction? Can we add water to a triglyceride to break it up into glycerol and 3 fatty acids?
Good question!
AUS-e-TUTE has new resources to help you understand the hydrolysis of triglycerides.
Members should log in to access the new tutorial, game, test and exam (with worked solutions).
If you are not an AUS-e-TUTE Member, you can access the "free-to-view" tutorial at
https://www.ausetute.com.au/hydrolysistg.html

Omega Fatty Acids

"Health Food" companies are always trying to sell us something new.
Instead of eating tasty fish they recommend we consume fish oil wrapped in plastic as a pill. Apparently this is because we are suddenly deficient in "omega-3 fatty acids".
So what are omega-3 fatty acids?
Where do they come from?
Do we really need them?

AUS-e-TUTE Members should log-in to access the new omega fatty acid resources (tutorial, game, test, exam).

If you are not an AUS-e-TUTE Member you can access a free-to-view tutorial at
https://www.ausetute.com.au/omegafat.html

Hydroxyacid or Carboxyalkanol?

So, you've learnt how to name organic molecules containing the OH (hydroxy) functional group, and, you can name molecules that have the COOH (carboxyl) functional group, the carbonyl functional group (C=O), and the NH₂ (amine) functional group.
Excellent!
But what happens when there are 2 or more different functional groups on the same molecule?
Can you still name it?
We can help!
AUS-e-TUTE has just added a new tutorial, game, test and exam to help you learn the IUPAC rules and confidently apply them to these sorts of molecules.
AUS-e-TUTE Members should log-in to use the new resources (under Organic Nomenclature).
If you are not an AUS-e-TUTE Member you can view the tutorial for free at
https://www.ausetute.com.au/nam2fung.html

Types of Structural Isomerism

If molecules have the same molecular formula but different structural formulae then they are called structural isomers and are said to display structural isomerism.
But there are different types of structural isomerism:

• chain isomerism (also known as skeletal isomerism)
• position isomerism (also known as regioisomerism)
• functional group isomerism (functional isomerism)

AUS-e-TUTE has just added new resources to help you learn about these types of isomerism and to help you apply this understanding when solving problems in chemistry.
AUS-e-TUTE Members should log-in to use the new tutorial, game and test.
If you are not an AUS-e-TUTE member yet, you can view a tutorial for free at https://www.ausetute.com.au/isomerism.html

How long is a piece of string?

How long is a piece of string?
What units of length you use to measure a piece of string will depend on how long the string is.
If you are putting up a string of Christmas lights you might measure the length of the string in metres or centimetres.
But if you are measuring the length of string, or ribbon, to tie back your hair you might measure the length of string in centimetres or millimetres.
1 centimetre is a hundredth of a metre: 1 cm = 10^-2 m
1 millimetre is a thousandth of a metre: 1mm = 10^-3 m
The metre is the SI base unit of length.
On the other hand, if your piece of string is holding 2 atoms together in a molecule you are going to need a very tiny piece of string, less than a billionth of a metre. Which is why chemists use units of length like the nanometre (1nm = 10^-9 m), the Ångstrom (1 Å = 10^-10 m), and the picometre (1 pm = 10^-12 m).
You will need to be familiar with these units and be able to convert one unit of length into another, so AUS-e-TUTE has just added new tutorials, games, tests to help our members do this.
If you are not a member, you can access a "free-to-view" tutorial at https://www.ausetute.com.au/lengthconv.html