Question

Give equations to show what happens when temporary hard water is boiled?

Answer 1

Hint : Hard water themselves are of two types i.e. permanent hard water and the temporary hard water. This classification of hard water is based on the presence of carbonates, sulphates and chlorides of Calcium and magnesium.

Complete Step By Step Answer:
So, temporary hard water can be defined as the water that contains carbonates or bicarbonates of calcium and magnesium.
On the other hand Permanent hard water is the water that contains the carbonates, bicarbonates, sulphates and chlorides of Calcium and magnesium.
So, since now we know the composition of the temporary hard water, we can easily tell the fate of temporary hard water on heating.
So, as we know that, temporary hard water contains the carbonates or bicarbonates of calcium and magnesium, so on heating these carbonates of calcium and magnesium decomposes.
Let’s have a look at the chemical equation for a better and clear understanding:
$Ca(HC{O_3})\xrightarrow{\Delta }CaC{O_3} + C{O_2} + {H_2}O$
$Mg(HC{O_3})\xrightarrow{\Delta }MgC{O_3} + C{O_2} + {H_2}O$
So, as we can see, calcium bicarbonate and magnesium bicarbonate ions that are present in the temporary hard water decompose on heating into calcium carbonate and magnesium carbonate respectively.
Also, in both the decomposition reactions, carbon-dioxide and water are produced as by-products.
So, these hard ions present in the hard water plays an important role in determining the chemical and physical properties of the hard water.

Note :
Hard water, whether it is temporary and permanent, is not fit for drinking purposes. Also, the hard water does not work well with the soaps, as they react with soaps to form a white precipitate known as scum. However, hard water can work with the detergents.