Chemistry HW Help

Question

What ratio of NaCN to HCN is needed to prepare a pH

10.30 buffer? (Ka of HCN is 4.9 × 10^-10)

Answer 1

Henderson Hasselbalch equation:

pH = pKa + log [NaCN] / [HCN]

pKa = -log Ka = -log 4.9x10^-10 = 9.31

10.30 = 9.31 + log [NaCN] / [HCN]

log [NaCN] / [HCN] = 0.99

[NaCN] / [HCN] = 9.8

So, the ratio of NaCN to HCN should be 9.8 to 1