Question

Permanent hardness is caused due to :
A) Magnesium bicarbonate
B) Magnesium carbonate
C) Magnesium sulphate
D) All of the above

Answer 1

Hint: The soaps tend to form an insoluble scum during the dissolution in water. We can also see a layer of white salt which is present on the utensils when the water dries up. The reason behind this is the hardness of water. The water is hard because of the chlorides of minerals which are present in it thus making it unfit for use.

Complete step-by-step answer:
The hardness of water is defined as the water which contains high content of minerals in it. The hardness is attained by water as it passes through the rocks which are made up of limestone, chalk or gypsum. The water has temporary hardness when it contains the minerals such as calcium hydrogen carbonate and magnesium hydrogen carbonate.

The permanent hardness of water is caused due to the presence of magnesium, sulfide and calcium in water. It is known as permanent hardness because it cannot be removed by boiling. If we need to remove this permanent hardness we need to treat it with washing soda. The permanent hardness of water is mainly due to the presence of sulphate in it.

So the correct answer for this question is option ‘C’.

Note: Students generally get confused between the heavy water and hard water. The heavy water contains deuterium instead of the hydrogen atoms while the hard water contains high mineral content in it. We express the hardness of water in parts per million (ppm).