Water

8.1 Hard and Soft Water

define hard water as water which does not readily lather with soap but gives scum

appreciate that hard water wastes soap but does not affect soapless detergents

recall that dissolved calcium and magnesium salts cause hardness

understand that hardness results from contact with limestone, chalk and gypsum

recall that boiling removes temporary hardness but not permanent hardness

explain that boiling removes temporary hardness but not permanent hardness

recall that both types of hardness can be removed by ion exchange and the addition of sodium carbonate

explain that both types of hardness can be removed by ion exchange and the addition of sodium carbonate

understand industrial and domestic problems caused by the deposition of scale

understand that the presence of hardness in water causes the inner surface of pipework to become coated, which prevents corrosion and the entry of poisonous salts of copper or lead into the water supply

8.2 Water Treatment

describe the treatment of water to make it suitable for domestic use

understand the need for sedimentation, filtration and chlorination

understand the reason for fluoridation