Chemistry 9701 · AS & A Level · Hydrocarbons

Hydrocarbons — practice question

Crude oil is a flammable liquid found naturally in the Earth and is a complicated blend of hydrocarbons. The hydrocarbons are separated from crude oil by means of fractional distillation.
(a(i))[1]

Explain what the term hydrocarbon means.

(a(ii))[1]

Explain what the term fractional distillation means.

(b(i))[2]

Undecane, $\text{C}_{11}\text{H}_{24}$, is a long-chain hydrocarbon present in crude oil. Long-chain hydrocarbons like these are cracked to make smaller molecules of alkanes and alkenes. Give the conditions for two different processes by which long-chain molecules may be cracked.

(b(ii))[3]

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

(c(i))[3]

Draw the three different structural isomers of pentane.

(c(ii))[6]

The three pentane isomers do not all have the same boiling point. Which of your isomers has the highest boiling point? Suggest an explanation for your answer.

(d)[2]

The unsaturated hydrocarbon, $E$, is made by cracking hexane and is significant in the chemical industry. The standard enthalpy change of combustion of $E$ is $-2059\ \text{kJ mol}^{-1}$. Define what is meant by the term standard enthalpy change of combustion.

(e(i))[2]

When $0.47\ \text{g}$ of $E$ was completely burnt 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 relevant data from the Data Booklet to calculate the amount of heat released in this experiment.

(e(ii))[2]

Use the data above together with your answer to (i) to calculate the relative molecular mass, $M_r$, of $E$.

(f)[1]

Deduce the molecular formula for $E$.

Worked solution & mark scheme

This 23-mark question has a full step-by-step worked solution and mark scheme. One marking point: A compound made up only of carbon and hydrogen

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