Question

Complex which is formed during the estimation of hardness of water is:
A) \[{{[Ca{{(S{{O}_{4}})}_{2}}]}^{2-}}\]
B) \[{{[Ca{{(HC{{O}_{3}})}_{6}}]}^{4-}}\]
C) \[{{[Ca(EDTA)]}^{2-}}\]
D) \[N{{a}_{2}}[C{{a}_{2}}{{(P{{O}_{3}})}_{6}}]\]

Answer 1

Hint: The complex is a coordination compound which contains a metallic element called a central metal atom so they are referred to as metal complexes. The complex contains a central metal atom and ligands in the coordination entity. There are two types of complexes: heteroleptic complexes in which the central atom is attached to different types of ligands whereas in homoleptic complexes the central atom is attached to the same type of ligands.

Complete step-by-step answer:
Hard water is the water which contains high mineral content. The formation of hard water takes place when the percolation of water occurs through the deposits of chalk and limestone which are formed by magnesium and calcium carbonates. There are two types of hard water, first is in which the hardness of water is not permanent that is temporary hard water and other is permanent hard water.

The presence of the magnesium and calcium carbonate makes the water temporarily hard whereas the presence of soluble salts of magnesium and calcium in chlorides make the water permanently hard.
So to estimate the hardness of water the EDTA is added in the presence of an EBT indication. So when we add EDTA, the calcium ions and magnesium ions readily form the complex with it and remove the hardness of water by forming the complex \[C{{a}^{2+}}{{[EDTA]}^{4-}}\]. The complex formed is \[{{[Ca(EDTA)]}^{2-}}\] which is a stable complex.

Hence the correct answer is option ‘C’.

Note: Hard water is safe to drink but it can cause strains in skin, can cause spots on clothes and linens. It can be removed by boiling and by Clarks method. The permanent hardness can be removed by Calgon’s process and Gan’s Permutit method.