What is [H3O+] and the pH of a solution of 0.052 M HNO2 and 0.041 M KNO2? Hint: This is a buffer.

Answer 1

Often times, when working with a buffer, you can use the Henderson Hasselbalch equation to solve the problem.

H.H.Equation: pH = pKa + log [salt] / [acid

pH = ?

pKa = -log Ka and Ka for HNO₂ is 4.0x10^-4. pKa = 3.40

[salt] = 0.041 M

[acid] = 0.052 M

Solving for pH, we have

pH = 3.40 + log 0.041 / 0.052 = 3.40 + log 0.788

pH = 3.40 + (-0.10)

pH = 3.30

From the pH, we can now find the [H₃O⁺]

pH = -log [H₃O⁺]

[H₃O⁺] = 1x10^-3.30

[H₃O⁺] = 5.01x10^-4 M