Chemistry Help Please!

Question

Calculate the pH of a buffer solution that is 0.250 M in HCN and 0.170 M in KCN. For HCN, Ka = 4.9 × 10^–10 (pKa = 9.31). Use both the equilibrium approach and the Henderson–Hasselbalch approach.

Answer 1

The Henderson -Hasselbalch equation is:

 

pH=pKa+log([A^-]/[HA])

 

where [HA] is the molarity of the acid and [A^-] is the molarity of its conjugate base.

 

Plugging in the numbers looks like this:

 

pH=9.31+log(0.170/0.250)

 

=9.14