Question

Each beaker in a series contains an identical sample of an acetic acid/sodium acetate buffer. The pH meter registers a value of 3.55. To each beaker the substance listed is added, and the pH again is measured. Assume this is done such that the total volume of the buffer does not change. In which beaker(s) will the pH remain at 3.55?

a. Beaker 1: 0.5 g NaCl is added

b. Beaker 2: 0.5 g KOH is added

c. Beaker 3: 0.005 mol HCl(g) is bubbled into the solution

d. Beaker 4: 0.5 g Ca(C2H3O2)2 is added

Answer 1

The beaker in which pH remains at 3.55 is (a.) Beaker 1: 0.5 g NaCl is added

Explanation

Sodium chloride NaCl is a neutral salt which will not change the pH of buffer.

In beaker 2, potassium hydroxide KOH, which is a strong base, is added which will react with acetic acid and convert acetic acid to acetate. This will increase the pH of the buffer.

In beaker 3, hydrochloric acid HCl, which is a strong acid, is added which will react with acetate and convert acetate to acetic acid. This will decrease the pH of the buffer.

In beaker 4, calcium acetate Ca(C₂H₃O₂)₂ , an ionic salt, is added which will dissociate completely to give calcium ions and acetate ions. This will increase the concentration of acetate ions and pH of buffer will increase.