pH and the ionic product of waterAQA A-Level Chemistry: Mind map

Exam questions on pH and the ionic product of water

1. A student dilutes 10.0 cm³ of 0.200 mol dm⁻³ hydrochloric acid with distilled water to a total volume of 250 cm³. All measurements are at 298 K.
   Calculate the pH of the diluted solution and the change in pH caused by the dilution.2 marks
2. A cleaning product contains sodium hydroxide at a concentration of 0.0250 mol dm⁻³. At 298 K the ionic product of water, Kw, is 1.00 × 10⁻¹⁴ mol² dm⁻⁶.
   Use Kw to calculate the hydrogen ion concentration in the original sodium hydroxide solution.2 marks
3. Pure water is slightly dissociated: H₂O(l) ⇌ H⁺(aq) + OH⁻(aq). A data book gives Kw = 1.00 × 10⁻¹⁴ mol² dm⁻⁶ at 298 K and Kw = 9.61 × 10⁻¹⁴ mol² dm⁻⁶ at 333 K.
   Show how the expression Kw = [H⁺][OH⁻] is derived from the equilibrium constant for the dissociation of water, and give the units of Kw.3 marks