H₂SO₄ + Zn = ZnSO₄ + H₂↑
2H⁺ + SO₄²⁻ + Zn = Zn²⁺ + SO₄²⁻ + H₂
2H⁺ + Zn = Zn²⁺ + H₂
H₂ + S = H₂S
H₂ + S = 2H⁺ + S²⁻
H₂S + Na₂O = Na₂S + H₂O
2H⁺ + S²⁻ + Na₂O = 2Na⁺ + S²⁻ + H₂O
2H⁺ + Na₂O = 2Na⁺ + H₂O
Na₂S + Fe(NO₃)₂ = 2NaNO₃ + FeS↓
2Na⁺ + S²⁻ + Fe²⁺ + 2NO₃⁻ = 2Na⁺ + 2NO₃⁻ + FeS
S²⁻ + Fe²⁺ = FeS