Answer
(a) pH increase.
(b) pH decrease.
(c) pH increase.
(d) No change.
(e) No change.
Work Step by Step
(a) and (c)
(i) $CH_3COOH(aq) + H_2O(l) \lt -- \gt CH_3COO^-(aq) + H_3O^+(aq)$
(ii) $HCOOH(aq) + H_2O(l) \lt -- \gt HCOO^-(aq) + H_3O^+(aq)$
- According to Le Chatelier's principle, if we add (i) acetate ions or (ii) formate ions, the equilibrium will try to consume the products, therefore reducing the $H_3O^+$ concentration and increasing the pH.
(b)
$NH_3 (aq) + H_2O(l) \lt -- \gt NH{_4}^+(aq) + OH^-(aq)$
- According to Le Chatelier's principle, if we add ammonium $(N{H_4}^+)$, the equilibrium will try to consume the products, reducing the $OH^-$ concentration, thus decreasing the pH.
(d) and (e)
$HCl(aq) + H_2O(l) -- \gt Cl^-(aq) + H_3O^+(aq)$
$HI(aq) + H_2O(l) -- \gt I^-(aq) + H_3O^+(aq)$
Since $HCl$ and $HI$ are strong acids, the addition of conjugate bases will not affect the equilibrium because it is already very products-favored.
