The pH of a 0.392 M solution of the conjugate base, A-, of a weak acid,...

The pH of a 0.392 M solution of the conjugate base, A-, of a weak acid, HA, is 11.60. What is the K_b for A-?

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Expert Solution

pH = 11.60

[ A- ] = 0.392 M

[H+] = 10^-pH

= 10^-11.60

= 2.5 x 10^-12 M

[OH-] = 1.0 x 10^-14 / 2.5 x 10^-12 = 4 x 10^-3 M

A- + H2O ---------------------> AH + OH-

0.392 0 0

0.392-x x x

x = [OH-] = 4 x 10^-3 M

Kb = x^2 / 0.392 -x

kb = (4 x 10^-3)^2 / (0.392 - 4 x 10^-3)

Kb = 4.12 x 10^-5

queen_honey_blossom answered 6 months ago

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