AQA GCSE Chemistry: Organic Chemistry

Crude oil is separated into useful fractions by fractional distillation in a fractionating column. The column is hot at the bottom and cooler at the top. Different fractions, such as bitumen, diesel oil and petrol, are collected at different heights.

Explain how fractional distillation separates crude oil into fractions, and explain why petrol is collected near the top of the column while bitumen is collected at the bottom. (6 marks)

Ethanol is an alcohol. It can be made by fermentation of sugar (glucose), or by the hydration of ethene.

(a) Name the functional group present in all alcohols, and give its formula. (1 mark)

(b) Ethanol can be oxidised to a carboxylic acid. Name the carboxylic acid formed when ethanol is oxidised, and name the functional group present in all carboxylic acids. (2 marks)

(c) When ethanol reacts with ethanoic acid (in the presence of an acid catalyst), an ester is produced. Name the other product formed in this reaction, alongside the ester. (1 mark)

Long-chain hydrocarbons from crude oil can be cracked to produce more useful, shorter-chain molecules.

An example of a cracking reaction is:

$C_{10}H_{22} \rightarrow C_8H_{18} + C_2H_4$C10​H22​→C8​H18​+C2​H4​

(a) Name the type of reaction shown (in terms of breaking down a large molecule). (1 mark)

(b) Describe one chemical test you could use to distinguish the product $C_2H_4$C2​H4​ (an alkene) from an alkane, and give the result for the alkene. (2 marks)

Poly(ethene) is made by addition polymerisation, whereas a polyester is made by condensation polymerisation.

(a) State one difference between addition polymerisation and condensation polymerisation in terms of the by-product formed. (1 mark)

(b) A polyester is made from two monomers: a dicarboxylic acid (–COOH groups at both ends) and a diol (–OH groups at both ends). Name the type of link formed between the monomers, and name the small molecule released each time a link forms. (2 marks)

DNA and proteins are examples of important natural polymers found in living things.

(a) Name the small molecules (monomers) from which proteins are made. (1 mark)

(b) State how many different monomers make up a molecule of DNA, and name the structure that a DNA molecule forms. (1 mark)

Alkanes are a homologous series of hydrocarbons with the general formula $C_nH_{2n+2}$Cn​H2n+2​.

Give the molecular formula of the alkane that contains 4 carbon atoms (butane). (1 mark)