Buffer solution - chemistry (5)

Question

Assume that 20 mL of a 0.10 molar HCl solution is added to 200 mL of a buffer mixture of Na2HPO4 and NAH2PO4 (in which both buffer components have a concentration of 0.050 molar). Which of the following statements is correct?

A. By adding 20 mL (0.10 molar) HCl, the proportion of HPO4^-2 compared to H2PO4^- in the buffer mixture increases.

B. Adding 20 mL of HCl (0.10 molar) will not change the acidity or pH.

C. Adding 20 mL of HCl (0.10 molar) to the buffer mixture causes the pOH to rise. (correct answer)

D. Adding 20 mL of HCl (0.10 molar) to the buffer mixture will cause NaCl to precipitate.

Answer 1

You are adding an acid to a solution which will make it more acidic by increasing the [H+], thus decreasing the pH. pH + pOH = 14. If pH decreases, then pOH increases.