Calculate the pH of a 0.390 M solution of NH4I?

Question

Thanks for the help in advance, and description of how you did it will also be helpful. Also to save you some time I do know that 0.408935393 is not the answer. Thanks for all the help.

Answer 1

1. look up pKb for NH3
2. subtract it from 14 to get pKa for (NH4)+, and thence Ka
3. work out [H+] = root (Ka x 0.39)
4. work out pH