Acidic, Neutral, and Basic Solutions of Salts

Key Concepts

• Salts in Solutions: When dissolved in water, salts can form acidic, neutral, or basic solutions.
• Sodium Chloride: Dissolves into sodium cations (Na+) and chloride anions (Cl-), resulting in a neutral solution (pH 7) at 25°C because neither ion reacts with water.

Salt Solution Types

1. Neutral Solutions

• Criteria: Neither cation nor anion reacts with water.
• Examples:
  • Sodium Chloride (NaCl): Sodium cation (Group 1A) and chloride anion (conjugate base of strong acid HCl) do not react with water.
  • Barium Nitrate (Ba(NO3)2): Barium cation (Group 2A) and nitrate anion (conjugate base of strong acid HNO3) do not react with water.

2. Basic Solutions

• Criteria: Anion reacts with water, cation does not.
• Mechanism: Anion hydrolysis increases hydroxide ion (OH-) concentration.
• Examples:
  • Barium Acetate (Ba(CH3COO)2): Acetate anion (conjugate base of weak acid acetic acid) reacts with water to form OH-.
  • Sodium Hypochlorite (NaOCl): Hypochlorite anion (conjugate base of weak acid hypochlorous acid) reacts with water to form OH-.

3. Acidic Solutions

• Criteria: Cation reacts with water, anion does not.
• Mechanism: Cation hydrolysis increases hydronium ion (H3O+) concentration.
• Examples:
  • Ammonium Nitrate (NH4NO3): Ammonium cation (NH4+) reacts with water to form H3O+.
  • Aluminum Chloride (AlCl3): Aluminum cation (Al3+) forms hydrated ions that interact with water to increase H3O+.

4. Solutions with Both Ions Reacting

• Criteria: Both cation and anion react with water.
• Outcome: Solution can be acidic, neutral, or basic.
• Example:
  • Ammonium Carbonate ((NH4)2CO3):
    • Ammonium Ion Reaction: Forms H3O+.
    • Carbonate Ion Reaction: Forms OH-.
    • Determining Solution Type: Compare Ka of ammonium and Kb of carbonate. If Ka < Kb, solution is basic.

Key Formulas

• Ka , \times , Kb = Kw: Used to determine acidity/basicity when both ions react with water.
• Kw = 1.0 , \times , 10^{-14} at 25°C.

Application

• Compare Ka and Kb values to determine whether solutions are acidic, neutral, or basic when both ions react.
• Use tables or literature for common Ka and Kb values.

Example Calculation

• Ammonium Carbonate: Calculated results show Kb > Ka, making the solution basic.
• Ka of Ammonium: 5.6 , \times , 10^{-10}
• Kb of Carbonate: 1.8 , \times , 10^{-4}