Question

Which of the following salt when dissolved in water produces hard water?
A.Calcium sulphate
B.Magnesium bicarbonate
C.Calcium chloride
D.Any of the above

Answer 1

Hint: Water having high concentrations of minerals and metal salts dissolved in it is known as hard water.

Complete step by step answer:
Salts of calcium and magnesium dissolved in water produce hardness of water. Principally sulphates, bicarbonates and chlorides of calcium and magnesium produce hardness of water.
Hardness of water can be of two types: temporary hardness and permanent hardness. Temporary hardness is caused by the presence of bicarbonates of calcium and magnesium in water. This hardness can be removed by boiling the water or by treating it with calcium hydroxide (known as lime softening), as this promotes the formation of carbonate from bicarbonate and the precipitate can be removed from the water, thereby leaving the water soft on cooling.
Permanent hardness is caused by the presence of sulphates and chlorides of calcium and magnesium in water. This hardness is difficult to remove and cannot be removed by boiling of water as precipitation of these salts does not take place. Water softeners and some other procedures can be used to remove permanent hardness.

Hence option D Is correct.

Note:
An indication of hard water is that lather formation in soaps does not take place when soap interacts with hard water. When the soaps are used in hard water, a solid substance known as scum forms. This is because charged calcium and magnesium particles (called ions ) present in the water react with soap to form an insoluble substance.