Question
Calculate the pH at the equivalence point in titrating 0.010 M solutions of each of the following with 0.081 M NaOH. (a) hydrochloric acid (HCl) pH = _?_ It's not 12.55
Explanation / Answer
Calculate the pH at the equivalence point in titrating 0.120 M...? Calculate the pH at the equivalence point in titrating 0.120 M solutions of each of the following with 8.0×10-2 M NaOH. A.) hydrobromic acid (HBr) B.) lactic acid (CH3CH(OH)COOH) Since HBr and NaOH are a strong acid and a strong base, the net ionic equation for the reaction is just: H+ + OH- --> H2O. So, the pH of that solution at the equivalence point will be 7.00. In the second case, the net ionic equation is: HLa + OH- --> La- + H2O. At the equivalence point, you will have a solution of sodium lactate. Since the lactate ion is a base, it will react with water as: La- + H2O HLa + OH- Kb for this reaction is: Kb = [HLa][OH-]/[La-] If you know Ka for lactic acid, you can calculate Kb because: Ka X Kb = Kw = 1 X 10^-14 So, in that solution, [HLa] = [OH-] = x. The expression for Kb becomes: Kb = x^2/0.12 = ______ You can solve the equation for x which equals [OH-]. From [OH-], you can calculate pOH and then pH, or you can calculate [H+] and then pH.