Sodium acetate (NaOAc) is the salt of a weak acid (Acetic Acid), and hence when

Question

Sodium acetate (NaOAc) is the salt of a weak acid (Acetic Acid), and hence when it is put in water a hydrolysis reaction occurs. Determine the concentrations of all species in a 0.30 M NaOAc aqueous solution. What is the equilibrium concentration of [OAc-]? (Express your numerical answer in units of millimolar, mM)

Sodium acetate (NaOAc) is the salt of a weak acid (Acetic Acid), and hence when it is put in water a hydrolysis reaction occurs. Determine the concentrations of all species in a 0.30 M NaOAc aqueous solution. What is the equilibrium concentration of [OAc-]? (Express your numerical answer in units of millimolar, mM)

Explanation / Answer

                   AcO-(aq) + H2O (l) <----> AcOH (aq) + OH- (aq)

Initially           0.3                                 0                 0

at equilibrium 0.3-X                               X                 X

Kb = [AcOH] [OH-] /[AcO-]                     Kb value is 5.56 x 10^-10

5.56 x 10^-10 = X^2 / ( 0.3-X)    we approximate 0.3-X = 0.3 since X is very small as Kb is very small

5.56 x 10^-10 = X^2 / ( 0.3)

X = 1.29 x 10^-5 M = [AcO-]

[AcO-] = 1.29 x 10^-2 mM    ( since 1mM = 10^-3M)

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