# If you have 200 grams of Na_2O, how many moles of Na_2O do you have?

You have $3$ and a bit moles of sodium oxide.
$\text{Moles "= " Mass"/"Molar mass}$ $=$ $\frac{200 \cdot g}{61.98 \cdot g \cdot m o {l}^{-} 1}$ $=$ ??" moles"
The signal advantage of doing calculations this way, i.e. including units in the calculation is that it adds an extra level of validation. I wanted an answer in $\text{moles}$. The calculation as given me an answer in $\text{moles}$, i.e. $\frac{200 \cdot \cancel{g}}{61.98 \cdot \cancel{g} \cdot m o {l}^{-} 1}$ $=$ ?mol. Why? Because $\frac{1}{x} ^ - 1$ $=$ $\frac{1}{\frac{1}{x}}$ $=$ $x$