Hydrocarbons - alkanes
AQA GCSE Chemistry revision on Hydrocarbons - alkanes. Aligned to the AQA GCSE Chemistry 8462 specification. This bank has 8 practice questions on this topic.
Sample questions (3 of 8)
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Question 1
The general formula for alkanes is...
- A) CnH2n+2
- B) CnH2n
- C) CnH2n-2
- D) CnHn
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Answer: CnH2n+2
All alkanes follow CnH2n+2: CH4 (n=1, 4H), C2H6 (n=2, 6H), C3H8 (n=3, 8H, propane), C4H10 (n=4, 10H, butane). All single bonds - 'saturated'. Compare alkenes (CnH2n - one double bond - 'unsaturated') and alkynes (CnH2n-2). Alkanes are stable, relatively unreactive - main use is as fuels.
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Question 2
Which of these is an alkane?
- A) Methane (CH4)
- B) Ethene (C2H4)
- C) Ethanoic acid (CH3COOH)
- D) Glucose
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Answer: Methane (CH4)
Methane (CH4) is the simplest alkane and the main component of natural gas. Used for: heating, cooking, electricity generation, hydrogen production. Also a potent greenhouse gas (28x more warming than CO2 over 100 years) - methane leaks from gas infrastructure + agriculture are climate concerns.
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Question 3
Crude oil is separated into useful products by...
- A) Distillation
- B) Electrolysis
- C) Cracking
- D) Adding chemicals
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Answer: Distillation
Crude oil is heated to ~400C - vaporises. Vapour rises up a fractionating column with a temperature gradient (hot bottom, cool top). Hydrocarbons condense at the height where the temperature equals their boiling point. Short molecules condense high (LPG, petrol). Long molecules condense low (diesel, fuel oil, bitumen). Different fractions = different products with different uses.
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5 more questions on Hydrocarbons - alkanes — plus mistakes tracking and spaced repetition across the whole Chemistry spec.