To solve this question, simply make an ICE Table with lactic acid reacting with water, thus it would be donating it's proton to water forming hydronium ions and the conjugate base of the acid. Given the initial concentration for lactic acid, place that in the initial column, and assuming that the equation is balanced and is 1 : 1, write the change in X as simply -X on the reactants and +X on the products. Knowing that we don't have any product to begin with, place zero for these concentrations, and simply solve for the appropriate expression in the equilibrium column, then plug the expressions into the Ka formula and make it equal to the acid ionization constant provided, then solve for x, by using the quadratic equation. Once done, knowing that the change in X on the products is for hydrogen ions along with the conjugate base.
Find the pH, by taking the negative logarithm of the equilibrium concentration that you have obtained.
