AQA GCSE Combined Science: Chemistry: Rates, Organic Chemistry and the Atmosphere
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.
Marble chips (calcium carbonate) react with dilute hydrochloric acid, giving off carbon dioxide gas. A student found that the reaction was faster when they used the same mass of marble as a powder instead of large lumps, and faster again when the acid was warmed.
Explain, using collision theory, why increasing the surface area of the marble and increasing the temperature of the acid both increase the rate of this reaction. (6 marks)
A student measured the total volume of gas produced when magnesium reacted with an excess of dilute hydrochloric acid. The results are shown.
| Time / s | Total volume of gas / cm³ |
|---|---|
| 0 | 0 |
| 10 | 32 |
| 20 | 52 |
| 30 | 62 |
| 40 | 66 |
| 50 | 66 |
(a) Calculate the mean rate of reaction, in cm³/s, over the first 20 seconds. Show your working and give the units. (2 marks)
(b) The reaction is fastest at the start and then gets slower. Using the data, explain why the rate is greatest at the start and why it eventually becomes zero. (2 marks)
Crude oil is a mixture of many different hydrocarbons. It is separated into useful fractions by fractional distillation.
(a) State what is meant by a hydrocarbon. (1 mark)
(b) Explain how fractional distillation separates crude oil into fractions, referring to boiling points and what happens in the fractionating column. (2 marks)
The Earth's atmosphere has changed enormously over billions of years. The early atmosphere is thought to have been produced largely by intense volcanic activity and contained very little oxygen, whereas today's atmosphere is about four-fifths nitrogen and one-fifth oxygen.
(a) Name the gas thought to have made up the largest proportion of the Earth's early atmosphere. (1 mark)
(b) Explain how the proportion of oxygen in the atmosphere increased over time, and what happened to much of the early carbon dioxide. (2 marks)
When fuels containing sulfur impurities are burned in vehicle engines and power stations, the gas sulfur dioxide (SO₂) can be released into the atmosphere.
State one environmental problem caused by sulfur dioxide, and state how sulfur dioxide is produced when such a fuel is burned. (2 marks)
Some reactions are reversible. In a reversible reaction the products can react to re-form the reactants.
Name the symbol used in an equation to show that a reaction is reversible. (1 mark)