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Arsenic acid (H3AsO4) is triprotic, with Ka1=5.5 x 10-3 (10 to the negative 3), Ka2=1.7 x...

Arsenic acid (H3AsO4) is triprotic, with Ka1=5.5 x 10-3 (10 to the negative 3), Ka2=1.7 x 10-7(10 to the negative 7), and Ka3=5.1 x 10-12 (10 to the negative 12). What is the pH of a 0.80 M solution of arsenic acid.,

Solutions

Expert Solution

concentration of arsenic acid = 0.80 M

H3AsO4 + H2O   -----------------> H2AsO4-   +   H3O+

0.80                                                   0                  0

0.80 - x                                                x                   x

Ka1 = [H2AsO4-][H3O+] / [H3AsO4]

5.5 x 10^-3 = x^2 / 0.80 - x

x^2 + 5.5 x 10^-3 x - 4.4 x 10^-3 = 0

x = 0.0636

[H3O+] = 0.0636 M

pH = -log [H+] = -log (0.0636)

pH = 1.20


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