Water is classified two types on the behaviour upon soap. These are:
1. Soft water: The water that forms lather with soap easily is called soft water. It contain no dissolved salts in it. Rain water, distilled water, dimineralized water are some of the examples of soft water.
2. Hard water: The water that does not forms lather with soap easily is called hard water. It contain dissolved salts ions like SO4—, CO3—, HCO3— of calcium and magnesium in it. Tap water, river water, spring water, sea water are some of the examples of hard water.
Note: Hardness of water is caused by the presence of soluble bicarbonates, chlorides, sulphate of calcium and magnesium. When hard water is added with the potassium and sodium salt of fatty acids from the soap, calcium and magnesium ions of hard water react with soap and forms insoluble curd of fatty acids. So lots of water is wasted and hard water is not considered suitable for washing purposes.
Types of hardness:
– Temporary hardness of water: This type of hardness is caused due to the presence of bicarbonates of calcium and magnesium. This type of hardness is removed by boiling the water.
– Permanent hardness of water: It is due to the presence of chlorides and sulphates of calcium and magnesium. This type of hardness is removed by washing soda process.
Note: In commercial scale, temporary hardness is removed by Clarke’s process.
Both temporary and permanent hardness can be removed by the following processes:
– Soda-lime process
– Calgon process
– Ion exchange method