Chem question help pleease?

Sodium stearate (C17H35COONa) is a major component of bar soap. The Ka of stearic acid is 1.3 × 10–5. What is the pH of 10.0 mL of an aqueous solution containing 0.42 g of sodium stearate

Answer:
Molecular weight = 306 g/mol
0.42 g / 306 = 0.00137 mole
M = 0.00137 / 0.01 L= 0.137 M
It is a strong salt >> Na+ + C17H35COO-
Now we have an hydrolisis
C17H35COO- + H2O <> C17H35COOH +OH-
initial concentration
0.137
at equilibrium
0.137-x .. . . . .. . . . . . . . . . . . . . x . . . . . .. . . . .x
The constant of this equilibrium Kh = Kw / Ka
Kh = 1 x10^-14 / 1.3 x 10^-5 = 7.69 x 10^-10
7.69 x 10^-10 = x^2 / 0.137 - x
x = [OH-] = 0.0000103 M
pOH = 4.99
pH = 14 - 4.99 = 9.01

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