7.1 Crude oil, hydrocarbons and alkanes
6 exam questions worth 8 marks. Write your answer, open the mark scheme, then give yourself the marks you earned. Your answers are saved on this device.
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What is the molecular formula of propane?
Choose one answer.
Correct Not quite: the answer is C3H8
Mark scheme
B
Model answer
B: propane has 3 carbon atoms, so C3H(2×3+2) = C3H8.
What is a hydrocarbon?
Mark scheme
- a compound of hydrogen and carbon only (1)
Model answer
A compound containing hydrogen and carbon atoms only.
Use the general formula of the alkanes to give the formula of the alkane with 10 carbon atoms.
Mark scheme
- C10H22 (1)
Model answer
\mathrm{C_nH_{2n+2}} with n = 10 gives C10H22.
Explain why alkanes are described as saturated.
Mark scheme
- they contain only single (C–C) bonds / cannot add more atoms (1)
Model answer
They have only single bonds between carbon atoms, so every carbon has four single bonds and no more atoms can be added.
Give two features of a homologous series.
Mark scheme
any two from:
- same general formula (1)
- differ by CH2 (1)
- similar chemical properties (1)
- trend in physical properties (1)
Model answer
Members have the same general formula and similar chemical properties.
Explain why crude oil is described as a finite resource.
Mark scheme
- it takes millions of years to form (1)
- it is being used up faster than it forms / will run out (1)
Model answer
It formed over millions of years from ancient biomass, and we are using it much faster than it can be replaced, so it will run out.
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