Answer
Step-by-Step pH Analysis for H₂SO₄ Solution (0.001 M)
- H₂SO₄ is a diprotic acid, meaning it can donate 2 protons (H⁺).
- The first dissociation is strong:
Ka₁ = ∞, so it fully dissociates:H₂SO₄ → H⁺ + HSO₄⁻ - This gives an initial [H⁺] = 0.001 M
- The second dissociation is weak:
Ka₂ = 10⁻²:HSO₄⁻ ⇌ H⁺ + SO₄²⁻ - Use an ICE table for the second dissociation:
HSO₄⁻ = 0.001 M initially
Let x = [H⁺] from second dissociation
Ka₂ = x² / (0.001 – x) ≈ x² / 0.001 = 10⁻²
→ x² = 10⁻⁵ → x ≈ 3.16 × 10⁻³
Let x = [H⁺] from second dissociation
Ka₂ = x² / (0.001 – x) ≈ x² / 0.001 = 10⁻²
→ x² = 10⁻⁵ → x ≈ 3.16 × 10⁻³
- Total [H⁺] = 0.001 (from first) + 0.00316 (from second) ≈ 0.00416 M
pH = -log(0.00416) ≈ 2.38 → ✅ A little less than 3
Correct Answer:
Option A: A little less than 3