# Question e79ab

Dec 9, 2017

#### Answer:

$6.0 \cdot {10}^{24}$

#### Explanation:

You can determine the number of atoms present in your sample by converting the mass of silicon to moles and by using Avogadro's constant.

To convert the mass of silicon to moles, use the molar mass of the element.

280 color(red)(cancel(color(black)("g"))) * "1 mole Si"/(28.086color(red)(cancel(color(black)("g")))) = "9.9694 moles Si"#

Now, you know that in order to have $1$ mole of silicon, you need to have $6.022 \cdot {10}^{23}$ atoms of silicon $\to$ this is given by Avogadro's constant.

You already know the number of moles present in your sample, so use Avogadro's constant to calculate the number of atoms present in your sample.

$9.9694 \textcolor{red}{\cancel{\textcolor{b l a c k}{\text{moles Si"))) * (6.022 * 10^(23)color(white)(.)"atoms Si")/(1color(red)(cancel(color(black)("mole Si")))) = color(darkgreen)(ul(color(black)(6.0 * 10^(24)color(white)(.)"atoms Si}}}}$

The answer is rounded to two sig figs, the number of sig figs you have for the mass of silicon.