# How many molecules are in a sample of water with a mass of 44.99 grams?

Mar 5, 2016

$\text{Mass "rarr" Moles "rarr" Number of molecules}$

#### Explanation:

To get the number of moles, we divide the mass by the molar mass:

$\frac{44.99 \cdot g}{18.01 \cdot g \cdot m o {l}^{-} 1}$ $=$ $2.50 \cdot m o l$.

Now by definition, in a mole of stuff there are $6.022 \times {10}^{23}$ individual items of that stuff.

So, in the given quantity of water, there are $6.022 \times {10}^{23} \cdot m o {l}^{-} 1 \times 2.50 \cdot m o l$ $=$ $15.04 \times {10}^{23} \text{ water molecules}$.

How many oxygen atoms in such a quantity; how many hydrogen atoms?