Buffers:

The following are sample non multiple choice questions taken from recent exams: These particular questions cover:

        • The common ion effect.
        • Polyprotic acids and pH.
        • Buffers-qualitative questions.
        • Buffer calculations.
        • Buffers & polyprotic acids:
          Addition of Acid or base
1.Calculate the approximate pH of a solution that contains 0.35 M of hydrofluoric acid and 0.62 M of sodium fluoride.
2.A solution initially contains 0.50 M of sodium fluoride and 0.62 M of hydrofluoric acid. The approximate pH of 1.0 L of this solution AFTER the addition of 0.20 moles of sodium hydroxide is ______. 
(Assume that the volume doesn't change, Ka for HF = 7.2x10-4).
3.Calculate the ratio of [NH4+]/[NH3] to give a buffer with pH = 10.0.