05 Chemical Bonds
06 Acids, Bases and Salts
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6.10.2 Effect of Heat on Salts

Heating Effect on Carbonate Salts

  1. All carbonates salts except potassium carbonate and sodium carbonate can be decomposed by heat to produce carbon dioxide gas. 
  2. 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

Heating Effect on Nitrate Salts

  1. All nitrates salts decompose when heated.
  2. Table below shows the products formed when different nitrate salts are heated.
Nitrate SaltEquation 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

Heating Effect on Sulphate Salts

  1. Most sulphate salts do not decompose by heat. For instance, sodium sulphate, potassium sulphate, and calcium sulphate are not decomposable by heat. 
  2. Only certain sulphate salts are decomposed by heat when heated strongly.
  3. 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.
      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

Heating Effect on Chloride Salts

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