Question

Find the pH of each of the following solutions of mixtures of acids.: 1. 0.170 M in HNO2 and 9.0×10−2 M in HNO3 2. 0.190 M in HCHO2 and 0.23 M in HC2H3O2 3. 5.0×10−2 M in acetic acid and 5.0×10−2 M in hydrocyanic acid

Answer 1

1. 0.170 M in HNO2 and 9.0×10−2 M in HNO3

Ka of HNO2 = 5.6 x 10^-4

concentration = 0.170 M

HNO2   --------------> H+ +   NO2-

0.170                          0          0

0.170 - x                     x           x

Ka = x^2 / 0.170 - x

5.6 x 10^-4 = x^2 / 0.170 - x

x = 9.48 x 10^-3

[H+] from HNO2 = 9.48 x 10^-3 M

[H+] from HNO3 = 9.0 x 10^-2 M

total [H+] = 0.09948 M

pH = -log [H+] = -log (0.09948)

pH = 1.0