Weak acids, Ka, Kw and strong basesEdexcel International A Level Chemistry: Mind map

Exam questions on Weak acids, Ka, Kw and strong bases

1. Benzoic acid, C₆H₅COOH, is a weak monoprotic acid used as a food preservative. At 298 K its acid dissociation constant, Ka, is 6.3 × 10⁻⁵ mol dm⁻³.
   Calculate the pH of a 0.0100 mol dm⁻³ solution of benzoic acid, stating the assumptions you make.2 marks
2. A technician works with aqueous solutions at 25 °C, at which the ionic product of water, Kw, is 1.00 × 10⁻¹⁴ mol² dm⁻⁶. At 50 °C the value of pKw is 13.26.
   Calculate the pH of 0.0150 mol dm⁻³ barium hydroxide solution, Ba(OH)₂, at 25 °C.2 marks
3. In Core Practical 11, a student dissolves 0.610 g of benzoic acid, C₆H₅COOH (M = 122.0 g mol⁻¹), in water and makes the solution up to 100 cm³ in a volumetric flask. The pH of the solution at 25 °C is measured as 2.75.
   Calculate the value of Ka for benzoic acid from these data, stating the units.3 marks