# How do you calculate the molar mass of heavy water?

Simply use the molar mass of deuterium, $2.0 \cdot g \cdot m o {l}^{-} 1$
For deuterium oxide, ""^2H_2O, ${D}_{2} O$, simply add up the molar masses of each element: $\left(2 \times 2.014 + 15.999\right) \cdot g \cdot m o {l}^{-} 1$ $\cong$ $20.0 \cdot g \cdot m o {l}^{-} 1$.