A buffer solution is made such that the initial concentrations of lactic acid (HC₃H₅O₃) and the lactate ion (C₃H₅O₃-) are both 0.600 M.What is the resulting pH if 10.0 mL of 1.00 M hydrochloric acid is added to 0.500 L of the buffer solution? (The K_a of HC₃H₅O₃ is 1.4 *10^-4.)

Question

Quizplus · Accepted Answer

The correct answer is A because the addition of hydrochloric acid will decrease the pH of the buffer solution. The pH of the buffer solution can be calculated using the Henderson-Hasselbalch equation:pH = pKa + log([A-]/[HA])where pKa is the acid dissociation constant, [A-] is the concentration of the conjugate base, and [HA] is the concentration of the acid.In this case, the pKa of lactic acid is 1.4 x 10^-4, and the initial concentrations of lactic acid and the lactate ion are both 0.600 M. Therefore, the initial pH of the buffer solution is:pH = 1.4 x 10^-4 + log([0.600 M]/[0.600 M]) = 3.82When 10.0 mL of 1.00 M hydrochloric acid is added to 0.500 L of the buffer solution, the concentration of lactic acid will increase and the concentration of the lactate ion will decrease. The new concentrations can be calculated using the following equations:[HA] = [HA]initial + [HCl]added[A-] = [A-]initial - [HCl]addedwhere [HA]initial and [A-]initial are the initial concentrations of lactic acid and the lactate ion, respectively, and [HCl]added is the concentration of hydrochloric acid added.In this case, [HA]initial = [A-]initial = 0.600 M, and [HCl]added = (10.0 mL)(1.00 M)/(0.500 L) = 0.0200 M. Therefore, the new concentrations are:[HA] = 0.600 M + 0.0200 M = 0.620 M[A-] = 0.600 M - 0.0200 M = 0.580 MThe new pH of the buffer solution can then be calculated using the Henderson-Hasselbalch equation:pH = 1.4 x 10^-4 + log([0.580 M]/[0.620 M]) = 3.82Therefore, the resulting pH of the buffer solution is 3.82.

A Buffer Solution Is Made Such That the Initial Concentrations