Page 235 - Chemistry ICSE Class IX

6 Hard and Soft Water

BASIC CONCEPTS

Soft Water
Water which forms good lather easily with soap or soap solution is called soft water. Soft water does not
contain any salt of calcium and magnesium.

Hard Water

Water which does not form lather with soap or soap solution is called hard water. Hard water forms curdy
precipitate with soap.
Hardness of water is due to the presence of dissolved calcium and magnesium bicarbonates, sulphates and
chlorides in it.

Types of Hardness of Water

There are two types of hardness of water: 6GORQTCT[ JCTFPGUU and 2GTOCPGPV JCTFPGUU.
y 6GORQTCT[ JCTFPGUU Water is said to be temporary hard when it contains calcium and magnesium
bicarbonates [or hydrogencarbonates, Ca(HCO ) , Mg(HCO ) ]. This type of hardness can be easily
3 2
3 2
removed simply by boiling.
boil
Ca(HCO ) (aq) o CaCO (s)p + H O(l) + CO (g)
2
3 2
2
3
y 2GTOCPGPV JCTFPGUU Water is said to be permanent hard when it contains sulphates and chlorides
of calcium and magnesium, (CaCl , CaSO , MgCl , MgSO ). Permanent hardness cannot be removed
4
4
2
2
by boiling. Permanent hardness can be removed by adding washing soda solution (dropwise) to the
water.
EXPERIMENT 6.1
Objective

To differentiate between hard water and soft water

Apparatus Required
Test tubes (2)

Materials Required

Soap solution, Two samples of water – one of soft water and the other of hard water. Labelled as sample
A and sample B.