Question

Find the pH and the concentration of each species of lysine in a solution of 0.010 M lysine HCl, lysine monohydrochloride.

Answer 1

There is the general dissociation:

HA + H2O = H3O + + A-

It has the expression of Ka:

Ka = [H3O +] * [A-] / [HA] = X ^ 2 / 0.01 - X

It is assumed that - X is negligible and clears:

X = [H3O +] = √Ka * 0.01 = √ 0.0071 * 0.01 = 0.0084 M

The pH is calculated:

pH = - log 0.0084 = 2.08

The concentrations are:

[Lys HCl] = 0.01 - 0.0084 = 0.0016 M

[Lys-] = [H3O +] = 0.0084 M

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