A student says: "Crude oil is a compound. Fractional distillation breaks its molecules into simpler hydrocarbons. Each fraction contains one pure substance."
Evaluate each part of this explanation.
[4 marks]AQA GCSE Combined Science November 2020 Chemistry Paper 2H
5 questions on this paper's topics
21:001 of 5
A factory uses 240 tonnes of a finite mineral each year. Process improvements reduce annual use by 15%. A managed forest supplies a different raw material that can regrow.
.1
Calculate the factory’s new annual mineral use.
[2 marks].2
Explain why the mineral remains finite and why a renewable resource is not automatically sustainable.
[2 marks]A reaction uses the same solution concentration at 20 °C and 35 °C. A student explains the faster reaction at 35 °C by saying particles are larger and the activation energy has decreased.
Evaluate the explanation.
[4 marks]Two laboratory ecosystem models both remove carbon dioxide by photosynthesis. In model A all dead plant material decomposes. In model B some material is buried where decomposition is very slow.
Explain which model better represents long-term carbon removal and why the amount photosynthesised alone is not enough to predict the long-term atmospheric change.
[4 marks]An exothermic synthesis gives the following measured data. At 250 °C: equilibrium yield 80%, time to equilibrium 40 min. At 350 °C: yield 60%, time 8 min. A plant must reach equilibrium within 10 min and obtain at least 55% yield.
.1
Calculate the factor by which equilibration is quicker at 350 °C.
[2 marks].2
Justify a temperature choice from these two settings and explain why the highest yield alone is not the best criterion.
[2 marks]