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Difficulty: MediumSalt Hydrolysis and Solution Acidity/Alkalinity

Match each aqueous salt solution (0.1 mol dm−30.1\text{ mol dm}^{-3}) to its corresponding pH nature resulting from salt hydrolysis.

  • Potassium ethanoate (CH3COOKCH_3COOK)Alkaline solution (pH>7pH > 7) due to anion hydrolysis
  • Ammonium chloride (NH4ClNH_4Cl)Acidic solution (pH<7pH < 7) due to cation hydrolysis
  • Sodium chloride (NaClNaCl)Neutral solution (pH=7pH = 7) with negligible hydrolysis
  • Ammonium ethanoate (CH3COONH4CH_3COONH_4)Neutral solution (pH≈7pH \approx 7) due to equal mutual hydrolysis of both ions

Answer

Potassium ethanoate matches with Alkaline solution (pH > 7) due to anion hydrolysis; Ammonium chloride matches with Acidic solution (pH < 7) due to cation hydrolysis; Sodium chloride matches with Neutral solution (pH = 7) with negligible hydrolysis; Ammonium ethanoate matches with Neutral solution (pH ≈ 7) due to equal mutual hydrolysis of both ions.
Potassium ethanoate (CH3COOKCH_3COOK) undergoes anion hydrolysis to yield hydroxide ions, producing an alkaline solution (pH>7pH > 7). Ammonium chloride (NH4ClNH_4Cl) undergoes cation hydrolysis to yield hydroxonium ions, producing an acidic solution (pH<7pH < 7). Sodium chloride (NaClNaCl) contains spectator ions from a strong acid and strong base, leading to negligible hydrolysis and a neutral solution (pH=7pH = 7). Ammonium ethanoate (CH3COONH4CH_3COONH_4) undergoes mutual hydrolysis of both cation and anion to equal extents, resulting in a neutral solution (pH≈7pH \approx 7).

Step-by-Step Solution

1
Classify each salt based on the strengths of its parent acid and parent base.
Potassium ethanoate comes from a weak acid (CH3COOHCH_3COOH) and strong base (KOHKOH). Ammonium chloride comes from a weak base (NH3NH_3) and strong acid (HClHCl). Sodium chloride comes from a strong acid (HClHCl) and strong base (NaOHNaOH). Ammonium ethanoate comes from a weak acid (CH3COOHCH_3COOH) and weak base (NH3NH_3).
Only ions originating from weak electrolytes undergo significant reaction with water (hydrolysis).
2
Determine the hydrolyzing species and the resulting ion produced in water.
For CH3COOKCH_3COOK, CH3COO−+H2O⇌CH3COOH+OH−CH_3COO^- + H_2O \rightleftharpoons CH_3COOH + OH^- (alkaline). For NH4ClNH_4Cl, NH4++H2O⇌NH3+H3O+NH_4^+ + H_2O \rightleftharpoons NH_3 + H_3O^+ (acidic). For NaClNaCl, no hydrolysis occurs. For CH3COONH4CH_3COONH_4, both ions hydrolyze equally.
Anion hydrolysis increases OH−OH^- concentration, whereas cation hydrolysis increases H3O+H_3O^+ concentration.
3
Correlate each salt to its solution pH characteristics.
CH3COOK→pH>7CH_3COOK \rightarrow pH > 7, NH4Cl→pH<7NH_4Cl \rightarrow pH < 7, NaCl→pH=7NaCl \rightarrow pH = 7, and CH3COONH4→pH≈7CH_3COONH_4 \rightarrow pH \approx 7.
The nature of the solution depends on which ion hydrolyzes or whether both hydrolyze to equal extents.

Key Concept

Salt Hydrolysis and Solution Acidity/Alkalinity
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Topics

Salt Hydrolysis and Solution Acidity/Alkalinity

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