pK_a(CH₃CO₂H) = 4.76

Calculate the pH of a solution containing
0.10

CH₃CO₂Na and 0.05

CH₃CO₂H.

K_a =	[H₃O⁺][CH₃CO₂^–]
	[CH₃CO₂H]

Relate pK_a (K_a) and pH (H₃O⁺) using

the K_a expression

[CH₃CO₂^–] ≈ 0.10

[CH₃CO₂H] ≈ 0.05

1.74 × 10^–5 =	[H₃O⁺] × 0.10
	0.05

[H₃O⁺] = 8.7 × 10^–6

pH = 5.06

Extent of reaction low for both solutes
Relate [CH₃CO₂^–] to initial concentration.
Relate [CH₃CO₂H] to initial concentration.

Entering the above into the K_a expression:

In solutions where the concentration of the base of the conjugate pair is higher than that of the acid

[H₃O⁺] must be lower than K_a for the system to be at equilibrium.

K_a = [H₃O⁺] ×	[conjugate base]
	[acid]

Thus pH is higher than pK_a.