Hardness of Water

Hard and soft Water

Water is a universal solvent. It can dissolve many substances. Some dissolved substances may be useful where some may not be. Mostly, the salts of various metals (mostly magnesium and calcium) like magnesium sulphate, calcium sulphate, magnesium chloride, magnesium bicarbonate, calcium chloride etc. are mixed in water which makes the hardness in water. There are two types of water, soft water and hard water. Hard water is a type of water which cannot form lather with soap and soft water is a type of water which can form lather with soap.
The hardness of water is of two types, permanent hardness and temporary hardness. Permanent hardness is due to chloride and sulphate salt of calcium and magnesium. In this type, the hardness of water cannot be removed easily. In a temporary type of hardness, the hardness of water can be removed by boiling the water. Temporary hardness of water is due to calcium bicarbonate and magnesium bicarbonate.

Removal of Temporary Hardness

There are various methods for the removal of temporary hardness of water. Some mostly used methods are discussed below,

1. By heating: As we know that, the temporary hardness of water is due to calcium bicarbonate and magnesium bicarbonate. When we heat, calcium bicarbonate and magnesium bicarbonate change into insoluble salts.
   Ca(HCO₃)₂ \( \overset{Heat}{\rightarrow}\) CaCO₃↓ + H₂O + CO₂
   
   Mg(HCO₃)₂\( \overset{Heat}{\rightarrow}\) MgCO₃ + H₂O + CO₂
   
   
2. Treating with lime water: Another way of removal of temporary hardness of water is by treating water with lime water. The chemical equation is given below,
   Ca(HCO₃)₂ + Ca(OH)₂→ 2CaCO₃↓ + 2H₂O
   
   Mg(HCO₃)₂+Ca(OH)₂→ MgCO₃ + CaCO₃↓ + 2H₂O

Removal of Permanent Hardness

Permanent hardness of water is due to the presence of salts such as magnesium chloride, magnesium sulphate, calcium chloride, etc. We can remove the permanent hardness of water by following methods which are highlighted below,

1. By treating with washing soda: Permanent hardness of water can be removed by treating it with washing soda. As we know that, the permanent hardness of water is due to soluble salts of calcium and magnesium so when we treat them with washing soda, it changes into insoluble salts.
   CaCl₂ + Na₂CO₃→ CaCO₃↓ + 2NaCl
   CaSO₄ +Na₂CO₃→CaCO₃↓ + Na₂SO₄
   MgCl₂ +Na₂CO₃→ MgCO₃↓ + 2NaCl
   MgSO₄ + Na₂CO₃→ MgCO₃↓ +Na₂SO₄
   
   
2. Permutit Process:

   

   One of the methods for removal of permanent hardness is Permutit process. In permutit process, sodium zeolite or sodium aluminium orthosilicate used which is prepared by fusing sodium carbonate silica and alumina. Its composition resembles Na₂Al₂SiO₈ or Na₂Z, where, Z stands for zeolite= Al₂SiO₈.
   At first in permutit process, the cylinder is packed with permutit. Then the hard water is passed through the cylinder. Here, the all the ions of soluble salts of calcium and magnesium are replaced by sodium ions. Since the amount of sodium ions decreases as it reacts with the ions of soluble salts of calcium and magnesium, this can be regenerated by soaking in a 10%solution of common salt when the reverse change takes place and calcium and magnesium ions pass into solution and sodium zeolite is formed again.
   
   Ca⁺⁺ + Na₂Z→ CaZ↓ + 2Na⁺
   Sodium zeolite
   Mg⁺⁺ + Na₂Z→ MgZ↓ + 2Na⁺
   Sodium zeolite
   [Note: Z = Al₂Si₂O₈.(H₂O)]
   
   
   
   
   

Advantages and Disadvantages of Hard Water

• Used in beer industries.
• Water becomes tasty to dissolved salts of calcium and magnesium.
• It helps in the development of bones and teeth as it contains calcium salt.

Disadvantage

• A large amount of soap is wasted.
• Unfit for drinking
• Unfit for use in the steam boiler.