Answer
🧪 pH Calculation of NH₄Cl Solution
1. Given Information
- Mass of NH₄Cl: 4.8 g
- Volume of solution: 150 mL = 0.150 L
- Molar mass of NH₄Cl: 53.5 g/mol
- Ka of NH₄⁺: 5.7 × 10⁻¹⁰
2. Step-by-Step Solution
Step 1: Calculate Moles of NH₄Cl
n = mass / molar mass = 4.8 g / 53.5 g/mol ≈ 0.0897 mol
Step 2: Calculate Concentration of NH₄⁺
[NH₄⁺] = moles / volume = 0.0897 mol / 0.150 L ≈ 0.598 M
Step 3: Write the Equilibrium Reaction
NH₄⁺ + H₂O ⇌ NH₃ + H₃O⁺
Using Ka expression:
Ka = [NH₃][H₃O⁺] / [NH₄⁺] = x² / 0.598
x² = (5.7 × 10⁻¹⁰)(0.598) = 3.42 × 10⁻¹⁰
x = √(3.42 × 10⁻¹⁰) ≈ 1.85 × 10⁻⁵ M
x = √(3.42 × 10⁻¹⁰) ≈ 1.85 × 10⁻⁵ M
Step 4: Calculate pH
pH = −log(1.85 × 10⁻⁵) ≈ 4.73
✅ Final Answer
The pH of the NH₄Cl solution is approximately 4.73.
This indicates a slightly acidic solution, which is expected from the hydrolysis of the ammonium ion (NH₄⁺).