Chemistry 9701 · AS & A Level · Hydrocarbons

Hydrocarbons — practice question

Crude oil is a flammable liquid that occurs naturally and is made of a complex blend of hydrocarbons. To separate the hydrocarbons, crude oil is heated and passed through fractional distillation.
(a(i))[1]

Explain what the term hydrocarbon means.

(a(ii))[1]

Explain what the term fractional distillation means.

(b(i))

Undecane, $\text{C}_{11}\text{H}_{24}$, is a long-chain hydrocarbon found in crude oil. Long-chain hydrocarbons like this are ‘cracked’ to make smaller alkane and alkene molecules. State the conditions for two different processes that can be used to crack long-chain molecules.

(b(ii))[3]

Undecane, $\text{C}_{11}\text{H}_{24}$, may be cracked to make pentane, $\text{C}_5\text{H}_{12}$, and an alkene. Write a balanced equation for this reaction.

(c(i))

Pentane, $\text{C}_5\text{H}_{12}$, shows structural isomerism. Draw the three structural isomers of pentane.

(c(ii))[6]

The three pentane isomers have different boiling points. Which of your isomers has the highest boiling point? Suggest a reason for your answer.

(d)[2]

Define the term standard enthalpy change of combustion.

(e(i))

When $0.47\,\text{g}$ of $E$ burned completely in air, the heat given out raised the temperature of $200\,\text{g}$ of water by $27.5\,^{\circ}\text{C}$. Assume that no heat was lost during the experiment. Use the relevant Data Booklet data to calculate the heat released in this experiment.

(e(ii))[4]

Use the information above and your answer to (i) to calculate the relative molecular mass, $M_r$, of $E$.

(f)[1]

Deduce the molecular formula of $E$.

Worked solution & mark scheme

This 18-mark question has a full step-by-step worked solution and mark scheme. One marking point: a compound containing just carbon and hydrogen

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