Video: GCSE Chemistry Higher Tier Pack 1 • Paper 2 • Question 6

GCSE Chemistry Higher Tier Pack 1 • Paper 2 • Question 6


Video Transcript

Poly(vinyl chloride), a commonly used plastic, is produced by the polymerisation of vinyl chloride. Complete the equation for this reaction by drawing the bonds in the displayed formulas of vinyl chloride and polyvinyl chloride.

Vinyl chloride is another name for chloroethane. You don’t need to know this to answer this question though. For the products, all you need to remember is that carbon forms four bonds, hydrogen forms one bond, and chlorine forms one bond. So the easiest thing to do is drawing single bonds to start with.

This leaves the chlorine and the hydrogens fully saturated. And the only space for one more bond which completes the four required by carbon is a carbon–carbon double bond. Now, we can move on to the product.

As the product is a polymer, we expect to see many monomers join together in an infinite chain. The carbon still has to form four bonds. The double bond opens up and joins one monomer to the next. We can finish off the bonds to hydrogen and chlorine. And there’s our answer: the key here is to have the bonds that join one monomer to the next pass through the brackets.

Nylon is an example of a polyamide. The reaction used to produce a polyamide is very similar to the formation of a polyester. The general equation for the reaction is a diamine, a molecule with two amine groups, reacting with a dicarboxylic acid, a molecule with two carboxylic acid groups, forming a polyamide, a polymer with amide linkages, and water.

Describe how the type of reaction used to produce poly(vinyl chloride) differs from the formation of a polyamide such as nylon.

The first thing to realise is that poly(vinyl chloride) is produced from a completely different type of polymerisation than nylon. Poly(vinyl chloride) is an addition polymer, meaning the monomers are added together without byproducts.

Well, nylon as can be seen from the reaction equation is a condensation polymer. It is produced from monomers that join together and eliminate a small molecule like water during the polymerization process. Something you should also see is that poly(vinyl chloride) is produced from a single monomer, vinyl chloride, whereas nylon is produced from two, a diamine and a dicarboxylic acid.

The chemistry of these two polymerisations is very different. Poly(vinyl chloride) is produced by the reaction of alkenes, whereas the polymerisation to produce nylon relies on the reaction between an amine and a carboxylic acid. Also, poly(vinyl chloride) has a hydrocarbon backbone, whereas the polyamide nylon has the amide linkages as well.

We now have more than enough information to answer the question.

Poly(vinyl chloride) is produced by addition polymerisation, whereas polyamides are produced by condensation polymerisation. The polymerisation of vinyl chloride involves one alkene monomer and the polymer is the only product. By contrast, the polymerisation forming a polyamide produces water as a byproduct and takes place between two monomers: a dicarboxylic acid and a diamine.

You could have also mentioned about the hydrocarbon chain and the amide linkages, but this answer is sufficient.

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