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Ch.16 - Aqueous Equilibria: Acids & Bases
Chapter 16, Problem 43b

The following pictures represent solutions of three salts NaA (A- = X-, Y-, or Z-); water molecules and Na+ ions have been omitted for clarity.
Three diagrams showing NaX, NaY, and NaZ salt solutions with A- anions and OH- ions.
(b) Which A- anion has the strongest conjugate acid?

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Conjugate Acids and Bases

In acid-base chemistry, a conjugate acid is formed when a base gains a proton (H+). The strength of a conjugate acid is inversely related to the strength of its corresponding base; a stronger base will have a weaker conjugate acid. Understanding this relationship is crucial for determining which anion (A-) has the strongest conjugate acid among the given salts.
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Conjugate Acid-Base Pairs

Acid-Base Strength and pKa

The strength of an acid is often measured by its pKa value, which is the negative logarithm of its acid dissociation constant (Ka). A lower pKa indicates a stronger acid, meaning it dissociates more completely in solution. In this context, comparing the pKa values of the conjugate acids formed from the anions X-, Y-, and Z- will help identify which anion corresponds to the strongest conjugate acid.
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Salt Hydrolysis

When salts dissolve in water, they can undergo hydrolysis, where the anions and cations interact with water molecules. This process can affect the pH of the solution, depending on whether the anions are derived from strong or weak acids. Anions from weak acids can lead to a more acidic solution, indicating that they have stronger conjugate acids, which is essential for answering the question about the strength of the conjugate acids of the anions.
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