Question

What is the molar mass of heavy water `"D"_2"O"`?

Answer 1

`"20.0276 g mol"^(-1)`

Explanation:

Heavy water, `"D"_2"O"`, is what you get when you replace the hydrogen-1 isotopes, `""^1"H"`, that are usually present in the vast majority of water molecules, with deuterium, or hydrogen-2 isotopes, `""^2"H"`.

The difference between hydrogen-1 and deuterium is that the latter contains one proton and one neutron inside its nucleus, as opposed to the former which only contains a proton.

Now, deuterium has a molar mass of

`M_("M D") = "2.0141 g mol"^(-1)`

https://en.wikipedia.org/wiki/Deuterium

This means that the molar mass of heavy water, which contains two deuterium isotopes and one oxygen atom, will be equal to

`M_("M D"_2"O") = 2 xx "2.0141 g mol"^(-1) + "15.9994 g mol"^(-)`

`color(green)(|bar(ul(color(white)(a/a)color(black)(M_("M D"_2"O") = "20.0276 g mol"^(-1))color(white)(a/a)|)))`