A-LevelChemistryEquilibria9701/42 · Oct/Nov 2020 · Q26 Marks
Write an expression for the Ka of the weak acid HA in terms of the concentrations of the species involved. Ka =
- (a)Write an expression for the Ka of the weak acid HA in terms of the concentrations of the species involved. Ka =[1]
- (b)The hydroxylammonium ion, HONH3+, is a weak acid. A 1.00 × 10⁻³moldm⁻³ solution of hydroxylammonium ions has a pH of 4.41.
- (b)(i)Calculate the Ka of HONH3+. Ka =[2]
- (b)(ii)Calculate the pKa of HONH3+. pKa =[1]
- (c)The solubility product of manganese(II) hydroxide, Mn(OH)2, in water is 1.1 × 10⁻¹¹ mol³ dm-⁹ at 298 K. Calculate the solubility of Mn(OH)2 in water at 298 K. solubility =[2]
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2020). The mark or mark type is shown in brackets.
- [1] [H+][A-]/ [HA]
- [1] [H+] = 3.9 × 10-5
- [1] Ka = 1.5 × 10-6
- [1] 5.82
- [1] 4 x³ = 1.1 × 10-11
- [1] x = 1.4 x 10-4
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