6.10.2 Effect of Heat on Salts

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Heating Effect on Carbonate Salts

All carbonates salts except potassium carbonate and sodium carbonate can be decomposed by heat to produce carbon dioxide gas.
Table below shows the effect of heating on metal carbonate.

Carbonate Salt	Equation of The Reaction
Potassium carbonate Sodium carbonate	Will not decompose by heat
Calcium carbonate Magnesium carbonate Aluminium carbonate Zinc carbonate Iron (III) carbonate Lead(II) carbonate Copper(II) carbonate	Calcium carbonate CaCO₃ → CaO + CO₂ Aluminium carbonate Al₂(CO₃)₃ → Al₂O₃ + 3CO₂ Copper carbonate CuCO₃ → CuO + CO₂
Mercury(II) carbonate Silver carbonate Aurum(II) carbonate	Silver carbonate 2Ag₂CO₃ → 2Ag + 2CO₂ + O₂
Ammonium carbonate	(NH₄)₂CO₃ → 2NH₃ + 2CO₂ + H₂O

Nitrate Salt	Equation of The Reaction
Ammonium nitrate	Ammonium nitrate decompose to nitrogen monoxide and water vapour when heated. NH₄NO₃ → N₂O + 2H₂O
Potassium nitrate Sodium nitrate	Potassium nitrate 2KNO₃ → 2KNO₂ + O₂ Sodium nitrate 2NaNO₃ → 2NaNO₂ + O₂
Calcium nitrate Magnesium nitrate Aluminium nitrate Zink nitrate Iron (III) nitrate Lead(II) nitrate Copper(II) nitrate	Magnesium nitrate 2Mg(NO₃)₂ → 2MgO + 4NO₂ + O₂ Iron(III) nitrate 4Fe(NO₃)₃ → 2Fe₂O₃ + 12NO₂ + 3O₂ Lead(II) nitrate 2Pb(NO₃)₂ → 2PbO + 4NO₂ + O₂
Mercury(II) nitrate Silver(I) nitrate Aurum(II) nitrate	Silver nitrate 2AgNO₃ → 2Ag + 2NO₂ + O2

Most sulphate salts do not decompose by heat. For instance, sodium sulphate, potassium sulphate, and calcium sulphate are not decomposable by heat.
Only certain sulphate salts are decomposed by heat when heated strongly.
For instance:
1. Strong heating of green crystal iron (II) sulphate will release steam, sulphur dioxide, sulphur trioxide and leave behind a reddish solid iron (III) oxide residue. The steam released comes from the hydrated water of the crystallize salt.
  2FeSO₄•7H₂O → Fe₂O₃(p) + SO₂(g) + SO₃(g) + 14H₂O(g)
2. Meanwhile, zinc sulphate, copper (II) sulphate, and iron (III) sulphate decompose when heated strongly to evolve sulphur trioxide gas and form a metal oxide.
  Example
  Zinc sulphate
  ZnSO₄ → ZnO + SO₃
  Copper (II) sulphate
  CuSO₄ → CuO + SO₃
  Iron (III) sulphate
  Fe₂(SO₄)₃→ Fe₂O₃ + 3SO₃
3. When ammonium sulphate is heated strongly, this white solid sublimate and is decomposed to form ammonia gas and sulphuric acid. vapour
  (NH₄)₂SO₄ → NH₃ + H₂SO₄

All chloride salts are not decomposable by heat except ammonium chloride.
Ammonium chloride sublimes and decompose to produce ammonia gas and hydrogen chliride gas.
For instance:
NH₄Cl → NH₃ + HCl