Chemistry 9701 · AS & A Level · Hydrocarbons

Hydrocarbons — practice question

A wide range of aliphatic and aromatic hydrocarbons exists.
(a)[2]

Name a naturally occurring source of aliphatic and aromatic hydrocarbons and describe how the different hydrocarbons are separated from this source.

(b(i))[1]

Alkanes are heated to high temperatures in the absence of air, causing the molecules to break into smaller molecules. Identify the reaction type.

(b(ii))[1]

Write an equation to show the reaction that happens when heptane, $\text{C}_7\text{H}_{16}$, is heated without air to produce only hexane, butane and ethene.

(c)[3]

The equation for the complete combustion of ethene is shown: $\text{C}_2\text{H}_4 + 3\text{O}_2 \rightarrow 2\text{CO}_2 + 2\text{H}_2\text{O}$. Calculate the volume, in $\text{dm}^3$, of carbon dioxide produced by the complete combustion of $1.00\,\text{g}$ of ethene at room temperature and pressure.

(d(i))[1]

During the first stage of the substitution reaction, chlorine forms chlorine free radicals. Explain what is meant by the term free radical.

(d(ii))[2]

Name and explain the type of bond breaking that takes place to form chlorine free radicals.

(d(iii))[1]

Name the stage of the reaction mechanism that happens when a methane molecule reacts with a chlorine free radical.

(d(iv))[1]

Complete the equation for the reaction that occurs when a methane molecule reacts with a chlorine free radical. $\text{CH}_4 + \cdot\text{Cl} \rightarrow$ ________ $+$ ________

(d(v))[2]

Carbon atoms can form $\sigma$ and $\pi$ bonds within hydrocarbon molecules. Explain the statement below with reference to $\sigma$ and $\pi$ bonds. Alkenes react with electrophiles but alkanes do not.

Worked solution & mark scheme

This 14-mark question has a full step-by-step worked solution and mark scheme. One marking point: Crude oil / petroleum is the source

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