Problem Example 5
Estimate the pH of a solution that is 0.10M in acetic acid (Ka = 1.8E–5) and .01M in formic acid (Ka = 1.7E–4).
Solution: Because Kw is negligible compared to the CaKa products, we can simplify (3-4):
[H+] = √(1.8E–6 + 1.7E-6) = .0019
Which corresponds to a pH of – log .0019 = 2.7
Note that the pH of each acid separately at its specified concentration would be around 2.8.