Question

Hard water required for an experiment is not available in school laboratories. However, the following salts are available in the laboratory. Which salts may be dissolved in water to make it hard for the experiment?
1. Calcium Sulphate
2. Sodium Sulphate
3. Calcium Chloride
4. Potassium Sulphate
5. Sodium hydrogen carbonate
6. Magnesium chloride
Which of the following options is correct?
A. 1,2 and 4
B. 1,3 and 6
C. 3,5 and 6
D. 2,4 and 5

Answer 1

Hint: As we all know that hard water consists of a high mineral content and mainly contains divalent cations. Hard water is mainly formed when water passes through the deposits of limestone and gypsum kind of salts.

Complete step by step solution: We all know that water is generally a crystal clear, odourless and tasteless substance but it consists of various minerals and chemicals and the presence of these minerals in water determines its hardness and softness.
Water consists of minerals like calcium and magnesium which are responsible for its hardness. Hard water is formed when water passes through the deposits of calcium and magnesium containing substances like limestone and gypsum. These minerals are beneficial for health and add flavours to the hard water. Water hardness can be classified into two types: temporary hardness and permanent hardness. The temporary hardness is caused by the presence of calcium bicarbonates and magnesium bicarbonates and permanent hardness is caused by the presence of calcium sulphate or calcium chloride and magnesium sulphate or magnesium chloride. To reduce the temporary hardness water can be simply boiled or it can be treated with calcium hydroxide. When soap reacts with calcium in water, it results in the formation of soap scum.
Therefore from the above explanation we can say that water in laboratories can be made hard using calcium chloride, calcium sulphates and magnesium chlorides.

Hence, the correct answer is (C).

Note: Hard water leaves spots on the washed dishes when they are dried whereas soft water does not leave any spot. Hard water is sometimes preferred as drinking water as it contains minerals and a certain flavour and soft water is normally salty in taste.