A 0.05 ~M aqueous solution of a weak base is 2 % ionised. The pH of this solution is:

Step-by-step solution

For a weak base, the hydroxide ion concentration is given by: [ OH ⁻ ] = C Given concentration C = 0.05 ~M and percentage ionisation = 2 % . Degree of ionisation, = 2 100 = 0.02 [ OH ⁻ ] = 0.05 0.02 = 0.001 ~M = 10⁻³ ~M pOH = - [ OH ⁻ ] = - (10⁻³) = 3 Assuming standard temperature ( 298 ~K ), pH + pOH = 14 pH = 14 - 3 = 11 The distractor 3 is incorrect as it represents the pOH , not the pH . The distractors 1.3 and 12.7 result from incorrectly treating the weak base as a strong base. Answer: 11