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