Question

A solution contains 0.0330 M Pb2 (aq) and 0.0330 M Sr2 (aq). If we add SO42–(aq), what will be the concentration of Pb2 (aq) when SrSO4(s) begins to precipitate?

Answer 1

The Ksp of PbSO₄ = 2.53 × 10⁻⁷
for srSO₄→ 3.44 × 10⁻⁷
for srSO₄
srSO₄→ Sr²⁺ + SO₄⁻
Ksp = [sr²⁺] [SO₄⁻]
3.44 ˣ 10⁻⁷ = (0.0330M) [ SO₄⁻]
[SO₄⁻] = 8.1 ˣ 10⁻⁶M
foe Pb SO₄
PbSO₄ →Pb²⁺ + SO₄⁻
Ksp = [ Pb²⁺] [ SO₄⁻]
2.53 ˣ 10⁻⁸M 
= [ Pb²⁺] (8.1 ˣ10⁻⁶M)
[Pb²⁺] = 2.75 ˣ 10⁻³M