Question
Answers

Temporary hardness is caused due to the presence of:
A.Magnesium sulfate
B.Magnesium chloride
C.Calcium sulfate
D.Magnesium carbonate

Answer Verified Verified
Hint:
Temporary hardness is the hardness that can be removed by boiling. Now, try to answer this question accordingly.

Complete step by step answer:
-Hard water is formed when normal water passes through the deposits of chalk and -limestone. These are made up of magnesium and calcium carbonates.
Magnesium and calcium carbonates in water make it temporarily hard. This type of hardness in water can be removed by boiling the water.
When we boil water, the soluble salts of $Mg(HCO_{ 3 })_{ 2 }$ present in it is converted to $MgCO_{ 3 }$ which is insoluble, and hence it gets precipitated and it is removed. We get the soft water after filtration.
-Here in this reaction, we can see soluble bicarbonates are converted into insoluble carbonates which are removed by filtration.
$Ca(HCO_{ 3 })_{ 2 }\quad \rightarrow \quad CaCO_{ 3 }\downarrow \quad +\quad H_{ 2 }O\quad +\quad CO_{ 2 }$
$Mg(HCO_{ 3 })_{ 2 }\quad \rightarrow \quad MgCO_{ 3 }\downarrow \quad +\quad H_{ 2 }O\quad +\quad CO_{ 2 }$

Therefore, we can conclude that the correct answer to this question is Magnesium carbonate that is option D.

Note:
-We should also know about permanent hardness. This is caused due to soluble salts of magnesium and calcium present in the form of chlorides and sulfides in water. This hardness cannot be removed by boiling.
-To remove this hardness we need to treat this water with washing soda. There is a formation of insoluble carbonates when washing soda reacts with the sulfide and chloride salts of magnesium and calcium. Hence, hard water is converted to soft water.