A Levels Chemistry (9701)•9701/12/M/J/21
Explanation
Empirical formula from molecular mass approximation for hydrocarbons
Steps:
- Straight chain hydrocarbons approximate the repeating CH2 unit (mass 14 g/mol).
- Divide molecular mass by unit mass: 84 / 14 = 6 units.
- Formula corresponds to (CH2)6 or C6H12.
- Empirical formula simplifies to lowest ratio CH2.
Why A is correct:
- Empirical formula is the simplest atom ratio; for hydrocarbons, molecular mass divided by CH2 unit mass (14) yields the ratio directly as CH2 when evenly divisible.
Why the others are wrong:
- B: Not enough information to confirm exact molecular formula without elemental composition data.
- C: Not enough information to confirm presence of C=C bond, as unsaturation type is unspecified.
- D: Not enough information.
Final answer: A
Topic: Hydrocarbons
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