Answer to Question #113167 in General Chemistry for Christopher Germain

Question

describe the process of calculating Ka from Ph for a 0.100M weak acid

Answer 1

The expression for the acid dissociation constant is written using equilibrium concentrations. So, if the reaction produced a concentration of hydronium ions equal to 10

−

4

M

, it follows that it also produced a concentration of conjugate base equal to 10

−

4

M

.

Because the initial concentration of the acid is considerably higher than the concentrations of the conjugate base and hydronium ions, you can approximate it to be constant.

This means that the acid dissociation constant for this acid will be

Ka=10−4*10−4 *0.100=1.0⋅10−7