250 mL of 1.0M lactic acid (C₃H₆O₃) is mixed with 500 mL of 1.0M lactate ion (C₃H₅O₃⁻). The Ka for lactic acid is 1.38 × 10⁻⁴. Determine the pH of this solution both before and after adding 0.1 moles of H3O⁺.