what is the pH of 0.80 M NaCN? What is the concentration of HCN in the solution?

Answer 1

The CN^- is hydrolyzed.
...........CN^- + HOH ==> HCN + OH^-
I.........0.8..............0.....0
C..........-x..............x.....x
E.........0.8-x............x.....x

Kb for CN^- = (Kw/Ka for HCN) = (x)(x)/(0.8-x) and solve for x = (OH^-) = (HCN)
This give you the HCN. Convert OH^- to pH.