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2017 O Level Chem P1 Q19 — Acids and Bases / pH and Strength Solution

Acids and Bases / pH and Strength 2017 O Level Pure Chemistry · Paper 1 · Q19

Question

Some statements about acids are given. 1 A 1 mol/dm³ solution of a strong acid will have a higher pH than a 1 mol/dm³ solution of a weak acid. 2 pH gives a measure of the H⁺ concentration in a solution. 3 Universal Indicator turns blue when placed in a solution of pH5. 4 When acids react with metals, hydrogen ions gain electrons. Which statements about acids are correct?

A1, 2 and 3
B1 and 2 only
C1 and 4 only
D2 and 4 only

Correct answer: D

Video Solution

Explanation

Answer: D. Statement 2 is correct (pH measures the hydrogen-ion concentration) and statement 4 is correct (when acids react with metals the hydrogen ions are reduced: \(2\text{H}^{+} + 2\text{e}^{-} \rightarrow \text{H}_2\)).

Statement 1 is wrong: a strong acid is more fully ionised, giving more \(\text{H}^{+}\) and a lower pH than a weak acid of the same concentration. Statement 3 is wrong: at pH 5 Universal Indicator is orange/yellow, not blue. So 2 and 4 only.

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