# Question 07ab7

Oct 12, 2017

$5.8 \cdot {10}^{21}$

#### Explanation:

Your tool of choice here is Avogadro's constant, which acts as the definition of a mole.

In order to have $1$ mole of sodium oxide, you need to have $6.022 \cdot {10}^{23}$ formula units of sodium oxide $\to$ this is known as Avogadro's constant.

$\textcolor{b l u e}{\underline{\textcolor{b l a c k}{\text{1 mole Na"_2"O" = 6.022 * 10^(23)color(white)(.)"formula units Na"_2"O}}}}$

So if you know for a fact that $1$ mole of sodium oxide contains $6.022 \cdot {10}^{23}$ formula units of sodium oxide, you can say that your sample will contain

9.7 * 10^(-3)color(red)(cancel(color(black)("moles Na"_2"O"))) * (6.022 * 10^(23)color(white)(.)"formula units Na"_2"O")/(1color(red)(cancel(color(black)("mole Na"_2"O"))))#

$= \textcolor{\mathrm{da} r k g r e e n}{\underline{\textcolor{b l a c k}{5.8 \cdot {10}^{21} \textcolor{w h i t e}{.} \text{formula units Na"_2"O}}}}$

The answer is rounded to two sig figs, the number of sig figs you have for the number of moles present in the sample.