AQA GCSE Chemistry (Triple) - Paper 2: Organic Chemistry

What is crude oil?

A finite mixture of hydrocarbons formed from the remains of ancient biomass.

What are hydrocarbons?

Compounds made up of only carbon and hydrogen atoms.

What are alkanes?

Saturated hydrocarbons containing only single bonds between carbon atoms.

What are the first four alkanes and their formulas?

Methane (CH4), Ethane (C2H6), Propane (C3H8), Butane (C4H10).

What are alkenes?

Unsaturated hydrocarbons that contain at least one carbon–carbon double bond (C=C).

What is the general formula for alkenes?

CnH2n.

What happens during combustion of hydrocarbons?

They react with oxygen to release energy.

What does complete combustion produce?

Carbon dioxide and water.

Why is incomplete combustion dangerous?

It produces carbon monoxide, a toxic gas that prevents blood from carrying oxygen.

What is fractional distillation?

The process of separating crude oil into fractions based on boiling points.

Why do different hydrocarbons have different boiling points?

Because larger molecules have stronger intermolecular forces and require more energy to separate.

What are the uses of different fractions from crude oil?

Refinery gases (fuels, LPG), petrol, kerosene, diesel, lubricating oils, bitumen (roads).

What is cracking?

Breaking long-chain alkanes into shorter, more useful alkanes and alkenes using heat.

Why is cracking important?

It produces alkenes used in making polymers and increases the supply of shorter, more useful alkanes.

What are the two types of cracking?

Thermal cracking (high temperature, no catalyst) and catalytic cracking (moderate temperature with a catalyst).

How can alkenes be tested for?

Using bromine water — it decolourises (from orange to colourless) when an alkene is present.

What happens in the reaction between alkenes and hydrogen?

Hydrogen reacts with alkenes in the presence of a nickel catalyst to form alkanes.

What happens in the reaction between alkenes and steam?

They form alcohols, e.g., ethene + steam → ethanol (requires high temperature and pressure).

What happens in the reaction between alkenes and halogens?

They form dihalogenoalkanes, e.g., ethene + bromine → dibromoethane.

What are alcohols?

Organic compounds with the functional group –OH. General formula: CnH2n+1OH.

Give examples of the first four alcohols.

Methanol, ethanol, propanol, butanol.

What are properties and uses of alcohols?

Dissolve in water, neutral pH, flammable. Used as fuels, solvents, and in alcoholic drinks.

How can ethanol be made?

By fermentation of sugar using yeast (anaerobic conditions, 30–40°C).

What are carboxylic acids?

Organic acids with the functional group –COOH. General formula: CnH2nO2.

Give examples of carboxylic acids.

Methanoic acid, ethanoic acid