Question

calculate the pH of a mixture that contains 0.16M of HCl and 0.21M of HBrO

Answer 1

When you have a mixture of a stron acid and a weak one you can ignore the weak because the amount of H+ produced by the strong one is huge in comparison with the amount produced by the weak, so the pH will not be really affected. I will do the calculation with the weak one and without it

[H+] from HCl= 0.16M ----> pH= -log 0.16= 0.796

Now considering HBrO:

HBrO ----> H+ + BrO-

Ka HBrO= 2x10^-9= [H+][BrO-]/[HBrO]= x²/0.21-x

Ka is really saml so we can ignore the -x.

Ka= x²/0.21 ----> x= [H+]= 2.05x10^-5M ---> total [H+]= 0.16M + 2.05x10^-5M= 0.1600205M ---> pH=0.796

It is the same! just ignore HBrO