Question

A solution is prepared by adding 100 mL of 1.0 M HC2H3O2 (aq) to 100 mL of 1.0 M NaC2H3O2 (aq). The solution is stirred and its pH is measured to be 4.73. After 3 drops of 1.0 M HCl are added to the solution, the pH of the solution is measured and is still 4.73. Which of the following equations represents the chemical reaction that accounts for the fact that acid was added but there was no detectable change in pH?(A) H3O+(aq) + OH−(aq) -> 2 H2O(l)
(B) H3O+(aq) + Cl−(aq) -> HCl(g) + H2O(l)
(C) H3O+(aq) + C2H3O2−(aq) -> HC2H3O2(aq) + H2O(l)
(D) H3O+(aq) + HC2H3O2(aq) -> H2C2H3O+(aq) + H2O(l)

Answer 1

Answer:

(C) H3O+(aq) + C2H3O2−(aq) -> HC2H3O2(aq) + H2O(l)

Explanation:

A buffer is a solution of a weak acid and its salt. It mitigates against changes in acidity or alkalinity of a system. A buffer maintains the pH at a constant value by switching the equilibrium concentration of the conjugate acid or conjugate base respectively.

Addition if an acid shifts the equilibrium position towards the conjugate acid side while addition of a base shifts the equilibrium position towards the conjugate base side.