6 exam-style questions with full mark schemes and model answers. Write your own answer and the AI examiner marks it against the mark scheme.
The Earth's atmosphere today is about 78 % nitrogen and 21 % oxygen, with a small amount of carbon dioxide. The very early atmosphere was very different — it was rich in carbon dioxide and contained little or no oxygen.
Describe and explain how the amounts of oxygen and carbon dioxide in the atmosphere changed over time to reach the composition we have today. (6 marks)
Long-chain hydrocarbons from crude oil are cracked to make more useful products. Decane is cracked as shown:
C10H22→C8H18+X
(a) Hydrocarbon X is an alkene. Deduce the molecular formula of X, and name it. (2 marks)
(b) Describe the result of the test with bromine water on alkene X, and on an alkane. (2 marks)
Burning fuels in vehicles and power stations releases pollutant gases into the atmosphere.
(a) Name the pollutant gas, formed when sulfur impurities in a fuel burn, that causes acid rain. (1 mark)
(b) Explain how carbon monoxide is formed when a fuel burns, and why it is dangerous. (2 marks)
Crude oil is a mixture of hydrocarbons. It is separated into useful fractions by fractional distillation in a fractionating column, which is hot at the bottom and cooler at the top.
Explain how fractional distillation separates crude oil into different fractions. (3 marks)
Tap water is potable (safe to drink) but is not the same as pure water.
(a) State the difference between potable water and pure water. (1 mark)
(b) Name one method used to kill microbes (sterilise) when producing potable water. (1 mark)
The alkanes are a family (homologous series) of hydrocarbons found in crude oil.
State the general formula of the alkanes. (1 mark)