State whether 1 M solutions of the following salts in water...

State whether $1 M$ solutions of the following salts in water would be acidic, basic, or neutral.
(a) $\mathrm{FeCl}_{3}$
(b) $\mathrm{BaI}_{2}$
(c) $\mathrm{NH}_{4} \mathrm{NO}_{2}$
(d) $\mathrm{Na}_{2} \mathrm{HPO}_{4}$
(e) $\mathrm{K}_{3} \mathrm{PO}_{4}$

Key Concepts

Amphiprotic Behavior

Amphiprotic ions are species that can function either as an acid or a base depending on the surrounding conditions. In salt solutions, ions that are amphiprotic may either accept or donate protons during their interaction with water, and the prevailing reaction is determined by the relative strengths (Ka and Kb) of the acid and base forms. This dual behavior influences the resulting pH of the solution.

Influence of the Parent Acid and Base Strengths

The acid–base character of a salt’s ions largely depends on the strengths of the original acid and base from which the salt is formed. If both the acid and base are strong, the resulting salt is neutral because neither ion reacts significantly with water. However, if one component is weak, its conjugate will more actively alter the pH of the solution through hydrolysis.

Ionic Charge Density

Ionic charge density plays an important role in the extent of hydrolysis. Metal cations with high charges and small ionic radii tend to polarize water molecules strongly, facilitating the release of protons and making the solution acidic. This concept explains why certain metal salts can lead to acidity in solution even if their anions do not hydrolyze appreciably.

Salt Hydrolysis

Salt hydrolysis is the process by which the ions from a dissolved salt react with water to form acidic or basic solutions. This concept explains that, when a salt dissociates, its anion and cation may interact with water, producing H+ or OH– ions depending on their chemical nature. The overall pH of the solution depends on the equilibrium established by these hydrolysis reactions.

Conjugate Acid?Base Pairs

Every ion produced from a salt’s dissociation is the conjugate acid or conjugate base of a weak base or weak acid, respectively. Anions that are the conjugate bases of weak acids tend to undergo hydrolysis to produce OH–, making the solution basic, whereas cations that are the conjugate acids of weak bases tend to donate protons, making the solution acidic.

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