Question

Heavy water is obtained by:

Answer 1

The formula of water is ${{H}_{2}}O$, so in this oxygen is attached with hydrogen but when the hydrogen is replaced with deuterium which is an isotope of hydrogen then we get hard water having formula ${{D}_{2}}O$. In every 6760 hydrogen atoms in the water, there is one atom of deuterium.

Complete answer:
We know that there are three isotopes of the hydrogen atom, i.e., hydrogen, deuterium, and tritium. These isotopes can change the hydrogen atom in the compounds. And as we know that normal water is a compound made up of hydrogen and oxygen whose formula is ${{H}_{2}}O$. So, when the hydrogen atom is replaced with deuterium then we get hard water having formula ${{D}_{2}}O$. The molecular weight of normal water is 18 but the molecular weight of hard water is 20.
We know that there are many sources from which we get the normal water. Ordinary water contains approximately one deuterium atom for every 6,760 ordinary hydrogen atoms in most natural sources. Deuterium oxide is virtually pure as hundreds of liters of water are electrolyzed and just a few milliliters remain. This process, which was the only large-scale method used until 1943, has been replaced by less costly methods like fractional distillation (${{D}_{2}}O$ becomes concentrated in the liquid residue because it is less volatile than ${{H}_{2}}O$).
So, we can say that the prolonged electrolysis of normal will make hard water.

Note:
The chemical name of normal water hydrogen oxide and the chemical name of hard water is deuterium oxide. When the tritium replaces the hydrogen from the water molecule we get ${{T}_{2}}O$ and it is a radioactive form of water.