The chemical formula of heavy water is D2O. Heavy water looks like water, but is about 10 percent heavier. In heavy water there is deuterium instead of hydrogen, and while regular hydrogen has one proton in its nucleus, the deuterium has both one proton and one neutron. Thus, it becomes heavier. It was a by product of the hydrogen gas that was produced at Vemork.
The molar mass of heavy water, which contains two deuterium isotopes and one oxygen atom, will be equal to
MMD2O=2×2.0141 g mol−1+15.9994 g mol−
MMD2O=20.0276 g mol−1