Question

What is the ph of a solution of 0.20 m hno2 containing 0.10 m nano2 at 25°c, given k a of hno2 is 4.5 × 10–4?

Answer 1

Answer is: pH of solution is 3.05.
c(HNO₂) = 0.20 M.
c(NaNO₂) = 0.10 M.
Ka(HNO₂) = 4.5·10⁻⁴.
This is buffer solution, so use Henderson–Hasselbalch equation: 
pH = pKa + log(c(NaNO₂) ÷ c(HNO₂)).
pH = -log(4.5·10⁻⁴) + log(0.10 M ÷ 0.20 M).
pH = 3.35 - 0.30.
pH = 3.05.