Mg + 2HCl = MgCl₂ + H₂↑;
Mg⁰ + 2H⁺ + 2Cl⁻ = Mg²⁺ + 2Cl⁻ + H₂↑;
Mg⁰ + 2H⁺ = Mg²⁺ + H₂↑.
2). 2Al(OH)₃ + 3H₂SO₄ = Al₂(SO₄)₃ + 6H₂O;
2Al(OH)₃ + 6H⁺ + 3SO₄²⁻ = 2Al³⁺ + 3SO₄²⁻ + 6H₂O;
2Al(OH)₃ + 6H⁺ = 2Al³⁺ + 6H₂O;
Al(OH)₃ + 3H⁺ = Al³⁺ + 3H₂O.
3). Fe + 2HCl = FeCl₂ + H₂↑;
Fe⁰ + 2H⁺ + 2Cl⁻ = Fe²⁺ + 2Cl⁻ + H₂↑;
Fe⁰ + 2H⁺ = Fe²⁺ + H₂↑;
4). H₂SO₃ = SO₂↑ + H₂O;
2H⁺ + SO₃²⁻ = SO₂↑ + H₂O.
5). FeCl₃ + 3NaOH = Fe(OH)₃↓ + 3NaCl;
Fe³⁺ + 3Cl⁻ + 3Na⁺ + 3OH⁻ = Fe(OH)₃↓ + 3Na⁺ + 3Cl⁻;
Fe³⁺ + 3OH⁻ = Fe(OH)₃↓.
4P + 5O₂ = 2P₂O₅;
4P⁰ + 5O₂ = 2P₂O₅;
P₂O₅ + H₂O = H₃PO₄;
P₂O₅ + H₂O = 3H⁺ + PO₄³⁻;
2H₃PO₄ + 6K = 2K₃PO₄ + 3H₂↑;
6H⁺ + 2PO₄³⁻ + 6K⁰ = 6K⁺ + 2PO₄³⁻ + 3H₂↑;
6H⁺ + 6K⁰ = 6K⁺ + 3H₂;
2H⁺ + 2K⁰ = 2K⁺ + H₂↑.