a sample of 20.0 mL of 0.100 M HCN (Ka=6.2*10^-10) is titrated with 0.150 M NaOH.

a) what volume of NaOH is used in this titration to reach the equivalence point?

b) What is the molar concentration of CN- at the equivalence point?

c) What is the pH of the solution at the equivalence point?

d) What is the pH of this solution when only 6.667 mL of the 0.150 M NaOH is added to 20.0 mL of the 0.100 M HCN?