Chemistry 9701 · AS & A Level · Hydrocarbons

Hydrocarbons — practice question

Crude oil is made up of a blend of hydrocarbons, together with other organic compounds whose molecules may include nitrogen, oxygen or sulfur. In an oil refinery, once crude oil has been separated by fractional distillation, several further processes can be applied, such as ‘cracking’, ‘isomerisation’, and ‘reforming’.
(a(i))

What does the term ‘cracking’ mean, and why is it done?

(a(ii))

Briefly describe how hydrocarbons would be cracked.

(a(iii))[4]

Write a balanced equation for the cracking of tetradecane, $\text{C}_{14}\text{H}_{30}$, to form heptane, $\text{C}_7\text{H}_{16}$.

(b)[1]

Ethanol, $\text{C}_2\text{H}_5\text{OH}$, boils at a higher temperature than $\text{C}_2\text{H}_5\text{SH}$. Give a reason for this difference.

(c(i))

Write a balanced equation for the burning of ethanethiol in excess air, producing three oxides of different elements.

(c(ii))[6]

Two of the oxides produced cause serious environmental harm. For each of these oxides, identify the pollution type it causes and describe one consequence of that pollution.

(d)[1]

A small amount of ethanethiol is added to liquefied gases such as butane, which are commonly used in portable cooking stoves. Suggest a reason for this.

(e)[3]

Sulfur-containing compounds are taken out of oil products at the refinery. The sulfur is recovered and converted into $\text{SO}_2$, which is then used in the Contact process. State the main operating conditions for the formation of $\text{SO}_3$ in the Contact process.

Worked solution & mark scheme

This 15-mark question has a full step-by-step worked solution and mark scheme. One marking point: Reduce large hydrocarbons to smaller hydrocarbons

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