The hydrated cation M1H2O26 3 + has Ka = 10-4, and the acid HA has Ka = 10-5. Identify the principal reaction in an aqueous solution of each of the following salts, and classify each solution as acidic, basic, or neutral. (a) NaA

Verified step by step guidance

1. Step 1: Identify the components of the salt NaA.
2. Step 2: Recognize that NaA is composed of Na^+ and A^-.
3. Step 3: Determine the nature of Na^+. Since Na^+ is the cation of a strong base (NaOH), it does not affect the pH and is considered neutral.
4. Step 4: Analyze the anion A^-. Since A^- is the conjugate base of the weak acid HA (with K_a = 10^{-5}), it can accept protons and thus will make the solution basic.
5. Step 5: Conclude that the principal reaction in the solution is the hydrolysis of A^-: A^- + H_2O \rightleftharpoons HA + OH^-, making the solution basic.

Key Concepts

Hydrated Cations and Their Acidity

Hydrated cations, such as M1H2O26 3+, can act as acids in solution by donating protons (H+) to water, leading to the formation of hydronium ions (H3O+). The strength of this acidic behavior is quantified by the acid dissociation constant (Ka), which indicates how readily the cation donates protons. A higher Ka value signifies a stronger acid, influencing the pH of the solution.

Acid-Base Equilibria

Acid-base equilibria describe the balance between acids and bases in a solution, governed by their respective Ka values. In this context, the acid HA with a Ka of 10-5 is weaker than the hydrated cation M1H2O26 3+ with a Ka of 10-4. This difference in strength determines the predominant species in solution and helps classify the resulting solution as acidic, basic, or neutral based on the concentration of H3O+ ions.

Salt Hydrolysis

Salt hydrolysis occurs when a salt dissolves in water and its constituent ions interact with water molecules, potentially altering the pH of the solution. For example, the salt NaA dissociates into Na+ and A- ions. The A- ion, being the conjugate base of the weak acid HA, can accept protons from water, leading to an increase in hydroxide ions (OH-) and resulting in a basic solution.