1). Al(OH)₃ + 3HCl = AlCl₃ + 3H₂O;
Al³⁺ + 3OH⁻ + 3H⁺ + 3Cl⁻ = Al³⁺ + 3Cl⁻ + 3H₂O;
3OH⁻ + 3H⁺ = 3H₂O.
2). 3KOH + FeCl₃ = 3KCl + Fe(OH)₃↓;
3K⁺ + 3OH⁻ + Fe³⁺ + 3Cl⁻ = 3K⁺ + 3Cl⁻ + Fe(OH)₃↓;
3OH⁻ + Fe³⁺ = Fe(OH)₃↓.
3). Fe(OH)₃ + 3HNO₃ = Fe(NO₃)₃ + 3H₂O;
Fe³⁺ + 3OH⁻ + 3H⁺ + 3NO₃⁻ = Fe³⁺ + 3NO₃⁻ + 3H₂O;
3OH⁻ + 3H⁺ = 3H₂O.
4). Ca(OH)₂ + CuSO₄ = CaSO₄ + Cu(OH)₂↓;
Ca²⁺ + 2OH⁻ + Cu²⁺ + SO₄²⁻ = Ca²⁺ + SO₄²⁻ + Cu(OH)₂↓;
2OH⁻ + Cu²⁺ = Cu(OH)₂↓.