Question

Question of 17 Enough of a monoprotic acid is dissolved in water to produce a 1.04 M solution. The pH of the resulting solution is 2.81. Calculate the K, for the acid. K, =

Answer 1

Answer

2.31×10^-6

Explanation

Dissociation equilibrium of monoprotic acid is

HA(aq) + H2O(l) <-------> A^-(aq) + H3O⁺(aq)

K_a = [A^-][H3O⁺] / [HA]

pH = -log[H3O⁺]

-log[H3O⁺] = 2.81

[H3O⁺] = 0.001549M

[H3O⁺] = [A^-]

[HA] = 1.04 - 0.001549 = 1.0385M

K_a = (0.001549)²/ 1.0385 = 2.31×10^-6