# What is the molecular mass of heavy water?

$20.03 \cdot g \cdot m o {l}^{-} 1$
Deuterium oxide, ${D}_{2} O$, or ""^2H_2O, has a molecular mass of $\left(15.999 + 2 \times 2.014\right) \cdot g \cdot m o {l}^{-} 1$
And $\rho = 1.11 \cdot g \cdot c {m}^{-} 3$, so you should be more buoyant if you swam in ${D}_{2} O$.