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

Aug 17, 2016

${\text{20.0276 g mol}}^{- 1}$

#### Explanation:

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

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"^(-)

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