Lactic acid has a pK_a of 3.08. What is the approximate degree of dissociation of a 0.35 M solution of lactic acid?

Question

Quizplus · Accepted Answer

The degree of dissociation can be calculated using the formula:

% Dissociation = [H+] / [HA] x 100%

where [H+] is the concentration of hydrogen ions produced from dissociation and [HA] is the initial concentration of the acid.

To calculate [H+], we need to know the equilibrium concentration of lactic acid, which can be found using the formula:

[H+] = (Ka x [HA]) / ([H+] + Ka)

where Ka is the acid dissociation constant and [H+] is the hydrogen ion concentration at equilibrium.

For lactic acid, Ka = 1.38 x 10^-4 and [HA] = 0.35 M. Substituting these values into the equation above and solving for [H+], we get:

[H+] = 8.89 x 10^-4 M

Now, we can calculate the degree of dissociation as follows:

% Dissociation = (8.89 x 10^-4 / 0.35) x 100% = 0.254%

Therefore, the approximate degree of dissociation of a 0.35 M solution of lactic acid is 0.254%, which is closest to 0.5%. The answer closest to this value is C, 4.8%.

Lactic Acid Has a PKa of 3

Lactic Acid Has a PK_a of 3