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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?

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

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.

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

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

Acids and bases (A-level only) Questions

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