Chemical Reactions & Equations

A magnesium ribbon burns in air with a dazzling white flame and produces a white powder of magnesium oxide. This is a combination reaction where two substances combine to form a single product.

Equation: 2Mg (s) + O₂ (g) → 2MgO (s)

When ferrous sulphate crystals are heated, they lose water of crystallisation and then decompose on strong heating. The colour changes from light green to reddish-brown.

Equation: 2FeSO₄ (s) → Fe₂O₃ (s) + SO₂ (g) + SO₃ (g)

Lead nitrate decomposes on heating to give lead oxide (yellow), nitrogen dioxide (brown fumes), and oxygen gas.

Equation: 2Pb(NO₃)₂ (s) → 2PbO (s) + 4NO₂ (g) + O₂ (g)

Water decomposes into hydrogen and oxygen on passing electric current. Hydrogen collects at the cathode (twice the volume) and oxygen at the anode.

Equation: 2H₂O (l) → 2H₂ (g) + O₂ (g)

Zinc displaces copper from copper sulphate solution. The blue colour of the solution fades and a reddish-brown deposit of copper is seen on the zinc strip.

Equation: Zn (s) + CuSO₄ (aq) → ZnSO₄ (aq) + Cu (s)

Iron nails are placed in copper sulphate solution. Iron displaces copper; the nails get a copper coating and the blue solution turns light green (iron sulphate).

Equation: Fe (s) + CuSO₄ (aq) → FeSO₄ (aq) + Cu (s)

Mixing barium chloride and sodium sulphate solutions produces a white precipitate of barium sulphate, which is insoluble in water.

Equation: BaCl₂ (aq) + Na₂SO₄ (aq) → BaSO₄ (s) + 2NaCl (aq)

On heating copper powder in air, the surface turns black due to formation of copper oxide (CuO). On passing hydrogen gas, the black coating disappears as copper is restored.

Equation: 2Cu (s) + O₂ (g) → 2CuO (s)

Hydrogen gas is passed over heated copper oxide. The black CuO is reduced back to reddish-brown copper. This demonstrates simultaneous oxidation and reduction (redox).

Equation: CuO (s) + H₂ (g) → Cu (s) + H₂O (l)