Q1(b)(ii). Ionic strength of 0.01 m H₂SO₄ + 0.02 m NaCl

Answer in brief

I=0.03+0.02=0.05 mol kg⁻¹ (H₂SO₄ taken as fully dissociated).

Key points

• Ionic strength: I=½Σᵢ mᵢzᵢ², summed over every ion in the solution. The charge enters as its square.
• H₂SO₄ → 2H⁺ + SO₄²⁻: m(H⁺)=0.02, m(SO₄²⁻)=0.01 I₁=½ (0.02×1²+0.01×2²)=½(0.02+0.04)=0.03 mol kg⁻¹ (=3m for a 1:2 electrolyte)
• NaCl → Na⁺ + Cl⁻: I₂=½ (0.02×1²+0.02×1²)=0.02 mol kg⁻¹ (=m for a 1:1 electrolyte)
• The contributions add (no reaction between the solutes): I=0.03+0.02=0.05 mol kg⁻¹