1)
Mg+H₂SO₄ = MgSO₄+H₂
Mg⁰+2H⁺+SO₄²⁻ = Mg²⁺+SO₄²⁻+H₂⁰
Mg⁰+2H⁺=Mg²⁺+H₂⁰
2)
2HCl + MgO = MgCl2 + H2O
2H⁺+2Cl⁻+MgO = Mg²⁺+2Cl⁻ + H₂O
2H⁺+MgO = Mg²⁺+H₂O
3)
Na2SO4 + Ba(OH)2 = BaSO4↓ + 2NaOH
2Na⁺+SO₄²⁻+Ba²⁺+2OH⁻ = BaSO₄↓ + 2Na⁺ + 2OH⁻
Ba²⁺ + SO₄²⁻ = BaSO₄↓
4)
2HNO3 + K2CO3 = 2KNO3 + CO2↑ + H2O
2H⁺+2NO₃⁻+2K⁺+CO₃²⁻ = 2K⁺+2NO₃⁻+CO₂↑+H₂O
2H⁺ + CO₃²⁻ = CO₂↑ + H₂O