Answer
$2.992\times10^{-23} grams$
Work Step by Step
A water molecule has the molecular formula of $H_{2}O$ and the molar mass of a water molecule is $18.02 g/mol.$ Therefore 18.02 grams of water contain $6.023\times10^{23}$ molecules of water. So to find the mass of one water molecule we can divide the two quantities to be left with grams; $\frac{18.02 g/mol}{6.023\times10^{23}} = 2.992\times10^{-23} grams$
