Calculate the concentration of the lactate ion in a solution that is 0.100 Min lactic acid (CH3CH(OH)COOH, pKa = 3.86) and 0.080 Min HCl.

Explanation:

pKa = 3.86

-log Ka = pKa

- log Ka = 3.86

Ka = 1 / ( 10^(3.86)) = 1.38 × 10⁻⁴

lactic → (H⁺) + lactate

but Ka ( equilibrium constant ) = ( H⁺) (lactate) / ( lactic acid)

when HCl dissociate, it forms

HCl → H ⁺ + Cl⁻

0.08 M of HCl will yield 0.08 M H⁺, lactate ion = 0.1 M

1.38 × 10⁻⁴ = (0.08) (lactate) / 0.1

(1.38 × 10⁻⁴  × 0.1) / 0.08 = lactate

lactate = 1.73 × 10⁻⁴