Question

Permanent hardness of water is due to
A. calcium carbonate
B. calcium chloride
C. calcium bicarbonate
D. calcium sulphide

Answer 1

Hint:The hard water contains a high amount of minerals. The main salts present in hard water are sulphate, halides and bicarbonates of alkaline earth metals. The bicarbonate produces temporary hardness. Sulphate and halides produced permanent hardness.

Complete answer:
On the basis of the concentration of ions, particularly calcium and magnesium, the water is divided into two parts: Hard water and soft water.

Hard water: the water contains a high amount of dissolved salts.
Soft water: the water contains a low amount of dissolved salts.

Hard water has a multivalent cation. The commonly present cations are calcium ${\text{C}}{{\text{a}}^{{\text{2 + }}}}$and magnesium${\text{M}}{{\text{g}}^{{\text{2 + }}}}$. The ions enter into the water for leaching. The ions are mixed into the water in the form of their minerals. The common minerals of calcium are gypsum and calcite and the mineral of magnesium is dolomite.
Calcium chloride is produced by hardness in water. Carbonates, bicarbonate and sulphide do not produce hardness. Boiling can remove temporary hardness. Permanent hardness is removed by specific methods such as permutit and calgon’s method.

Therefore, option (B) calcium chloride, is the correct answer.

Note:Soft water contains monovalent cations such as sodium chloride and potassium chloride whereas hard water contains multivalent cations. The hard water can be converted into soft water by the ion exchange method, permutit method or by using calgon’s method. In all methods, generally ion producing hardness get exchanged with sodium ions. Permuted method is used for filtration of hard water. Filtration removes the impurities. Permutit is an artificial zeolite. Permutit has a porous structure. The pores can trap ions of specific size.