Question

Temporary hardness can be removed by mixing water with slaked lime, this process is known as softening of water.

• A. True
• B. False

Answer 1

The correct option is A True

Removal of hardness from water can be done by using different methods that can be grouped into two: chemical (use of chemical softeners) and mechanical (physical) methods.

Chemical Method of Removing Water Hardness utilizes water Softeners. These are of two types: those which lead to precipitation; and those which do not precipitate. Calculated amount of slaked lime or calcium hydroxide is added to the water to remove dissolved calcium, magnesium or iron(II) salt by forming precipitate or undissolved solids. The precipitate is then removed by filtration. It will remove only temporary hardness from water.

Reaction involved:

$Ca\left(OH{)}_2\right(s)+Ca(HCO3{)}_2\left(aq\right)\to 2CaC{O}_3\left(s\right)+2H_{2}O$

$Ca(OH{)}_2$ is slightly soluble; $Ca(HC{O}_3{)}_2$ is soluble; $CaC{O}_3$ is insoluble. Excess of slaked lime could cause hardness, hence the amount added is measured.

Therefore option A is correct