Final answer:
To find the Ka for 0.10 M lactic acid with a pH of 2.44, calculate the hydronium ion concentration, then apply it to the Ka expression. The dissociation constant is approximately 1.32 x 10^-4.
Step-by-step explanation:
To calculate the acid dissociation constant (Ka) for lactic acid based on a pH of 2.44, we can follow these steps:
- First, we need to convert the pH into the hydronium ion concentration ([H3O+]) by using the formula: [H3O+] = 10-pH. For a pH of 2.44, this would be: [H3O+] = 10-2.44 ≈ 3.63 x 10-3 M.
- Because lactic acid (denoted HA) is a weak acid, the initial concentration of A- (the conjugate base) is negligible, and the equilibrium concentration of A- will be equal to [H3O+] due to the 1:1 stoichiometry in the dissociation equation HA ⇌ H+ + A-.
- Now we can use the expression for Ka which is: Ka = [H3O+][A-]/[HA]. Since [H3O+] ≈ [A-] and considering the initial concentration of lactic acid is 0.10 M, the expression becomes: Ka = (3.63 x 10-3)2 / (0.10 - 3.63 x 10-3) ≈ 1.32 x 10-4.
The acid dissociation constant for lactic acid in a 0.10 M solution with a pH of 2.44 is approximately 1.32 x 10-4.