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Acids and bases (A-level only)

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Question 27

Values of the ionic product of water (KwK_wKw​) at different temperatures are given:

  • Kw=4.00×10−14 mol2 dm−6K_w = 4.00 \times 10^{-14} \text{ mol}^2 \text{ dm}^{-6}Kw​=4.00×10−14 mol2 dm−6 at 45∘C45 ^\circ\text{C}45∘C
  • Kw=9.61×10−14 mol2 dm−6K_w = 9.61 \times 10^{-14} \text{ mol}^2 \text{ dm}^{-6}Kw​=9.61×10−14 mol2 dm−6 at 60∘C60 ^\circ\text{C}60∘C

Which statement is correct?

A

The pH of pure water at 45∘C45 ^\circ\text{C}45∘C is 7.007.007.00.

B

The concentration of hydroxide ions in pure water at 60∘C60 ^\circ\text{C}60∘C is 3.10×10−7 mol dm−33.10 \times 10^{-7} \text{ mol dm}^{-3}3.10×10−7 mol dm−3.

C

The self-ionization of water is exothermic because KwK_wKw​ increases with temperature.

D

At 60∘C60 ^\circ\text{C}60∘C, pure water is slightly acidic because its pH is less than 7.007.007.00.

Markscheme

Acids and bases (A-level only) Questions

  1. A Level
  2. /Chemistry
  3. /Acids and bases (A-level only)

77 exam-style questions on AQA A Level Chemistry Acids and bases (A-level only), covering Brønsted–Lowry acid–base equilibria in aqueous solution (A-level only), Definition and determination of pH (A-level only), The ionic product of water, $K_w$ (A-level only), Weak acids and bases $K_a$ for weak acids (A-level only), pH curves, titrations and indicators (A-level only), and Buffer action (A-level only). Each one has a worked solution and a mark scheme showing where the marks go.

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