Question

The accepted value for the ionization constant of acetic acid is 1.76x10^-5. Using this figure, calculate the H+ concentration of 0.70?M HOAc.

Answer 1

The accepted value for the ionization constant of acetic acid is 1.76x10^-5. Using this figure, calculate the H+ concentration of 0.70?M HOAc.

                                               AcOH      <------ > H⁺ + AcO^-

Initial concentration       0.70 M                      0         0

Conc. At Eq^m.                   (0.70 – X)                 X          X ………………………(X be the concentration of ions at eq^m.)

Ka for this dissociation is,

Ka = [H⁺][AcO^-]/[AcOH]

1.76 x 10-5 = (X x X) / (0.70 – X)…………………..(1)

X <<< 0.70 as acetic acid is weak acid,

Hence, 0.70 – X = 0.70 (apprx.)

With this value in eq.1 we get,

1.76 x 10^-5 = X² / 0.70

X2 = 0.70 x 1.76 x 10^-5

X2 = 1.232 x 10^-5

Taking square roots of both sides,

X = (1.232x10^-5)^1/2

X = 3.51 x 10^-3

Hence [H⁺] = 3.51 x 10^-3

H⁺ ion concentration in 0.70 M AcOH is 3.51 x 10^-3

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