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2020 O Level Chem P1 Q31 — Separation Techniques / Immiscible Liquids Solution

Separation Techniques / Immiscible Liquids 2020 O Level Pure Chemistry · Paper 1 · Q31

Question

A liquid mixture contains a hydrocarbon and water. The boiling points and densities of the hydrocarbon and of water are shown in the table. Which statements about this liquid mixture can be deduced? 1 The hydrocarbon will form a layer below the water layer. 2 The hydrocarbon is methane. 3 The mixture can be separated using a separating funnel. Question diagram

Question diagram

A1, 2 and 3
B1 and 2 only
C1 and 3 only
D3 only

Correct answer: D

Video Solution

Explanation

Answer: D (statement 3 only). Statement 1 is wrong. The hydrocarbon has a lower density (0.8) than water (1.0), so it floats and forms a layer above the water, not below it. Statement 2 is also wrong: methane is a gas at room temperature, with a boiling point far below 0 \(^\circ\)C, whereas this hydrocarbon is a liquid with a boiling point of 130 \(^\circ\)C, so it must be a larger hydrocarbon, not methane.

Statement 3 is correct. The hydrocarbon and water are immiscible and form two separate layers, so they can be separated using a separating funnel by running off the lower water layer.

Only statement 3 can be deduced, so the answer is D. Common error: assuming the hydrocarbon sinks; always compare densities, since the less dense liquid floats on top.

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