[bobsmith1000]

My friend's little brother asked me this question, and I was sad to say I was befuddled. It seems as though there wasn't enough information (no K_a given!)

A buffer solution has .14 moles of HCN and .15 moles of KCN in 1 L of solution.

a) What's the pH of this buffer?
b) What's the pH of the solution from (a) after adding .01 moles of sodium hydroxide?
c) What's the pH of the solution from (a) after adding .01 moles of nitric acid?

I know HCN is a weak acid, and I know how to use the Henderson/Hasselbach equation, but this question is just crazy.

Any suggestions?

[AWK]

b.
0.14 mole HCN + 0.01 mole NaOH = 0.013 mole HCN + 0.01 mole NaCN
since in buffer CN- ion work, uyou have 0,16 mole of cyanide
c.
Analogously HCN incereses, NaCN decreases

[Borek]

pK_a = 9.31. In this kind of question you can't do anything without pK_a, which means you have to look it up.