Problem summary

Consider 0.10

CH₃CO₂Na.
pK_a(CH₃CO₂H) = 4.76

Estimate the pH of the solution:
The pH is higher than 7.
One of the major species in solution is a weak base!

Calculate the pH of the solution.
Relate pK_a (K_a) and pH (H₃O⁺) using

the K_a expression and
the reaction ocurring to reach equilibrium

K_a =	[CH₃CO₂^–][H₃O⁺]
	[CH₃CO₂H]

CH₃CO₂^– + H₂O

CH₃CO₂H + OH^–

Relate [CH₃CO₂^–] to initial concentration.
Relate [CH₃CO₂H] to pH (H₃O⁺)

using the reaction ocurring to reach equilibrium and
K_w

[CH₃CO₂^–] ≈ 0.10

[CH₃CO₂H] = [OH^–]
[CH₃CO₂H] = K_w/[ H₃O⁺]

Entering the above into the K_a expression:

The pH is consistent with the estimate.
Note that [OH^–] = 7.6 × 10^–6.
Thus the approximation that the extent of reaction is low is justified.

1.74 × 10^–5 =	0.10 × [H₃O⁺]
	10^–14 /[H₃O⁺]

[H₃O⁺] = 1.31 × 10^–9

pH = 8.88