Question

4. (10 pts) Lactic acid C3H603 is found in sour milk where it is produced by the action of lactobacilli in lactose or the sugar in milk. The pH of a 0.045 M solution of lactic acid was determined using a pH probe and found to be 2.63. a. Calculate the equilibrium constant for this acid. b. Had you not been given the pH of the acid and you had to measure it yourself, how would the method in part 2 be applied to the determination of Ka? Would you expect an improvement in the accuracy of your result with the application of the method of this experiment? Explain why or why not.

Answer 1

Given a) Lactic acid is found in sour milk where it is produced by the action of lactobacilli in laclose or the sugor in milk → The pH of a 0.045M solution of lactic acid was determined using a PH probe and found to be 2.63 » [H , 10 lo” 6 2 → [HA] = 0.045M → so in equilibrium [++] - [A] = 102.63 (HA): 0.045-102.63 y to [H+][*] (10269) (10*2163) [HA (0.045 - 102.63) ta = 0.10991379362 Theretou. *a = 1.099x10 b) It he assess PH, this should be more precise value than a. theoritical.