What is the pH of a 0.10 M H2Se solution

Question

What is the pH of a 0.10 M H2Se solution that has the stepwise dissociation constants Ka1 = 1.3 × 10-4 and Ka2 = 1.0 × 10-11?

1. a. 2.44

2. b. 3.89

3. c. 5.50

4. d. 4.89

I assume that it only needs to be calculated from the first due to the second pKa being so low, I just needed to make sure.

Answer 1

H2Se <----> H+ + HSe-

1.3 x 10^-4 = x^2 / 0.1-x

x = [H+] = 0.0036 M

pH = 2.44

We can neglet the Ka2