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2022 O Level Chem P1 Q33 — Petroleum / Combustion Solution

Petroleum / Combustion 2022 O Level Pure Chemistry · Paper 1 · Q33

Question

The table shows the number of carbon atoms present in the molecules in four of the fractions of petroleum. One mole of a compound in fraction F is completely burned in excess oxygen. The reaction produces 17 mol of water. Assuming the compound in fraction F is saturated, what would be a use for this fraction? Question diagram

Question diagram

Aa source of polishes and waxes
Bfeedstock for other organic reactions
Cfuel for aircraft engines
Dmaking road surfaces

Correct answer: C

Video Solution

Explanation

Answer: C. Find the molecular formula first, then match the carbon count to a fraction in the table.

Complete combustion of an alkane: \(\text{C}_n\text{H}_{2n+2} + \tfrac{3n+1}{2}\text{O}_2 \rightarrow n\text{CO}_2 + (n+1)\text{H}_2\text{O}\). From 1 mol of compound, water moles = \(n + 1 = 17\) → \(n = 16\). So the compound is \(\text{C}_{16}\text{H}_{34}\) — 16 carbons.

From the table, 16 carbons falls in the paraffin (kerosene) range of 12–18. Kerosene's main industrial use is fuel for aircraft engines (jet fuel). Option C.

A (polishes/waxes) describes lubricating oils (19–25 C).
B (feedstock) describes naphtha (6–11 C).
D (road surfaces) describes bitumen (>35 C).
Only C matches the 12–18 C paraffin range that 16 carbons falls into.

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