How to find the amount when you have...?

How do I find the amount of NaC2H3O2 that must be dissolved to produce 2.0L of a solution whose [OH] is 1.0*10-5?

Answer:
NaC2H3O2 is a strong electrolyte :
NaC2H3O2 >> Na+ + C2H3O2-
When is put in water we get :
C2H3O2- + H2O <> CH3COOH + OH-
the constant of this equilibrium called hydrolysis constant can be written as
Kh = Kw/Ka = 1 x 10^-14 / 1.8 x 10^-5 = 5.6 x 10^-10
For this equilibrium
[OH-] = [ CH3COOH ] = 1.0 x 10^-5
[CH3COO-] = x - 1.0 x 10^-5
5.6 x 10^-10 = ( 1.0 x 10^-5)^2 / x - 1 x 10^-5
x - 1 x 10^-5 = 1.0 x 10^-10 / 5.6 x 10^-10 = 0.178
x = 0.178 M
to get 2 L we need 0.178 x 2 = 0.356 mole NaC2H3O2
molar mass = 82 g/mol
0.356 x 82 = 29.2 g

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How to find the amount when you have...?

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