The pH of a 0.01 M HCN solution (Ka = 6 x 10-10) would be approximately

The pH of a 0.01 M HCN solution (Ka = 6 x 10^-10) would be approximately

a) 1–2

b) 3-4

c) 5-6

d) 6-7

Solution: HCN is a weak acid and we would expect the pH to be lower than 7, but not too low (that would be strong acids). We would expect the pH to be around 5-6. Alternatively, we can make an ICE chart and calculate the pH.

HCN <-> H+ + CN-

I 0.01 0 0

C -x x x

E 0.01-x x x

Ka = 6 x 10^-10 = x^2/ 0.01-x

x = 2.45 *10^-6= [H+]

pH = -log[H+] = 5.61