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: By using a method called Clark's method which is done by adding hydrogen of that alkaline earth metal which is having atomic number $20$ by that calcium and magnesium ions in water get dissolved. That water which contains magnesium or calcium ions is known as hard water while soft water contains lower concentration of these ions.

Complete step-by-step answer:When we want to wash the clothes, we generally see that detergent or soap get easily mixed in hot water and not in cold water. Scum is produced when there is not a good solubility and when not good foam is produced. We call this as hardness of water, when water consists of larger concentrations of magnesium and calcium ions then it is known as hard water. But when the concentration of these ions gets lower than it is called soft water.
There are many methods, where the hardness of water can be decreased so one of the methods includes the reaction with slaked lime. What slaked lime is, it is called calcium hydroxide having formula as $Ca{(OH)_2}$ . This method is also called lime softening, thus we can remove the hardness of water by adding calcium hydroxide.

Option C is correct.

Note: In Clark's method, lime is added to the hard water, which precipitates the calcium ions as calcium carbonate and magnesium as magnesium hydroxide. These precipitation is removed when we filter the solution. Reaction can be written as, $Ca{(HC{O_3})_2}\, + \,Ca{(OH)_2}\, \to \,2CaC{O_3}\, + \,2{H_2}O$ same reaction can be written for magnesium ions where magnesium hydroxide get precipitated.