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Form 4 Chemistry online lessons on acids, bases and salts

Permanent hardness of water and how it is removed

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Answer Text:
Permanent hardness
- Is that due to soluble sulphates and or chlorides of calcium and or magnesium and cannot be removed by boiling
Removal of permanent hardness
(i). By the addition of washing soda (sodium carbonate)
- Washing soda softens hard water by causing the formation of insoluble $CaCO_3 or MgCO_3$
- The soluble sodium salts left in water do not react with soap.
Equations:
$Na_2CO_3(aq) + CaCl_2(aq) to 2NaCl(s) + CaCO_3(s)$
Ionically:
$Ca^(2+)(aq) + CO_3^(2-)(aq) to CaCO_3(s)$
$Na_2CO_3(aq) +MgSO_4(aq)to Na_2SO_4(s) +CaCO_3(s)$
Ionically:
$Mg^(2+)(aq) + CO_3^(2-)(aq) to MgCO_3(s)$
- This method is very convenient and economical on large scale. It softens both temporary and permanent hardness
(ii). By permutit softener (ion exchange); explanations as before
(iii). Distillation.