How would the pH values of equal molar solutions of the...

How would the pH values of equal molar solutions of the following salts compare (highest, lowest, etc.)? $\mathrm{NaH}_2 \mathrm{PO}_4$, $\mathrm{Na}_2 \mathrm{HPO}_4$, and $\mathrm{Na}_3 \mathrm{PO}_4$.

Key Concepts

Salt Hydrolysis

This concept refers to the reaction that occurs when a salt’s ions interact with water, leading to the formation of acidic or basic solutions. Understanding salt hydrolysis is crucial because it determines whether the resulting solution will have a higher or lower pH based on the nature of the cations and anions derived from the parent acid and base.

Conjugate Acid?Base Pairs

A conjugate acid?base pair consists of an acid and its corresponding base formed by the loss or gain of a proton. In salt solutions, the ion derived from a weak acid can act as a conjugate base and accept protons from water, thereby raising the pH, while the ion derived from a weak base can donate protons to water, lowering the pH.

Acid-Base Equilibrium

Acid-base equilibrium involves the reversible reactions between acids, bases, and water that determine the concentration of hydrogen ions in solution. This equilibrium is quantified by dissociation constants (Ka for acids and Kb for bases) which are key to predicting how the solution’s pH will shift when different ions are present.

Polyprotic Systems

Polyprotic systems are those in which an acid or its conjugate base can donate or accept more than one proton. The stepwise deprotonation or protonation leads to multiple equilibria with different strengths (pKa values). Understanding these multiple equilibria is essential when evaluating salts derived from polyprotic acids because each ion’s ability to alter pH depends on its particular position in the deprotonation series.

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