Question

The buildup of lactic acid in muscles causes pain during extreme physical exertion. the ka for lactic acid (c2h5ocooh) is 8.4 × 10−4 . calculate the ph of a 0.06 m solution of lactic acid. 1. 2.297 2. 11.851 3. 2.174 4. 2.043 5. 2.149 6. 6.348 7. 1.926 8. 3.533

Answer 1

Answer is: pH of lactic acid is: 3. 2.174.
Chemical reaction: C₃H₆O₃(aq) ⇄ C₃H₅O₃⁻(aq) + H⁺(aq).
c(lactic acid - C₃H₆O₃) = 0,06 M.
Ka(C₃H₆O₃) = 8.4·10⁻⁴.
[H⁺] = [C₃H₅O₃⁻]  = x.
[C₃H₆O₃] = 0.06 M - x.
Ka = [C₃H₅O₃⁻] · [H⁺] / [C₃H₆O₃].
8.4·10⁻⁴ = x² / (0.06 M -x).
Solve quadratic equation: x = [H⁺] = 0.0067 M.
pH = -log[H⁺].
pH = -log(0.0067 M) = 2.17.