Question

Temporary hardness of water can be removed by adding:
A.$NaOH$
B.$N{a_2}C{O_3}$
C.$Ca{(OH)_2}$
D.$MgC{l_2}$

Answer 1

Hint:Temporary hardness of water is due to the presence of dissolved bicarbonate minerals such as calcium bicarbonate and magnesium bicarbonate. Thus, to remove the temporary hardness of water we have several methods such as boiling and by Clarks method. Also, apart from temporary hardness, water also has permanent hardness and we can remove it by Gan’s Permutit method, Calgon’s process and ion exchange resin method.

Complete answer:
The above question belongs to the concept of hardness of water. Hardness of water is the amount of mineral content present in it. It is because of the presence of salts of calcium and magnesium ions. Hard water does not lather with soap and thus, it is not suitable for laundry.
Hardness is also of two types. One is permanent and the other is temporary hardness. The difference between these two is that, in case of temporary hardness, salts of calcium and magnesium are present in the form of bicarbonates but in case of permanent hardness, salts of calcium and magnesium are present in the form of chloride.
Here, we are talking about temporary hardness and how it can be removed. We have two methods to remove temporary hardness.
First one is boiling, in this case when we boil the water the bicarbonates get converted to carbonates. Second way to remove temporary hardness is by Clarks method. In this method the hardness is removed by calcium hydroxide which is also known as Clarks reagent. When we add calcium hydroxide in the water, it converts bicarbonates and carbonates.
Thus, we can conclude that by adding calcium hydroxide \[Ca{(OH)_2}\] temporary hardness of water can be removed.

So, option C is the correct answer.

Note:
In this question we can see that temporary hardness of water can be removed by many methods like boiling and by Clarks method but only in case of Clarks method we are adding a reagent to remove the hardness not in boiling method. Also remember that temporary hardness and permanent hardness are completely different and thus we require different methods to remove hardness.