Question

What is [H3O+ ] (in M) in a solution of 0.078 M HBrO2 and 0.036 M NaBrO2? (Assume Kw = 1.01 ✕ 10^−14.)

HBrO_2(aq) + H_2O(l) <--> H_3O^+(aq) + BrO_2^−(aq); Ka = 3.7 ✕ 10−4

Answer 1

Use the Henderson-Hasselbalch equation.
pH = pKa + log (base)/(acid). You have Ka, convert to pKa.
You have the acid (HBrO2) and the base(BrO2^- from NaBrO2).
Post your work if you get stuck.