Question

The reactions of heavy water are slow. The reason is:
A. heavy water is associated.
B. heavy water is dissociated .
C. heavy water is of higher mass.
D. heavy water is of lower mass.

Answer 1

Heavy water is made up of deuterium , that is why heavy water is also known as deuterium oxide. Molecular formula of heavy water is ${D_2}O$ and that of normal water is ${H_2}O$ . An hydrogen atom is made up of one electron and one proton but a Deuterium is made up of a proton ,an electron and a neutron.

Complete step by step answer:
As we know that deuterium has a neutron but a hydrogen atom does not have a neutron. This makes the deuterium more heavier than the hydrogen atom. The heavy water has greater mass as compared to that of normal water because of that extra neutron of the deuterium. One other factor that we need to consider in this context is that the bond strength of oxygen atom with the deuterium atom is stronger than that of oxygen atom and hydrogen atom. For this reason the bond between the deuterium atom and oxygen atom is hard to break and that is why the reaction of heavy water is slower. From the above explanation it is clear to us that the answer of the given question is heavy water is of higher mass.

Hence option C is correct.

Note:
The molecular mass of heavy water that is ${D_2}O$ is $20.02g$ and the molecular mass of normal water that is ${H_2}O$ is $18.01g$ . Heavy water is miscible in normal water. Deuterium is not radioactive. Hydrogen has isotopes out of which tritium is radioactive which has two neutrons.