# Question 982c7

May 4, 2017

Here's what I got.

#### Explanation:

The thing to remember here is that you can't go directly from grams to *atoms, you have to go through moles first.

To convert the number of grams of sulfur to moles, use the element's molar mass

40 color(red)(cancel(color(black)("g"))) * "1 mole S"/(32.065color(red)(cancel(color(black)("g")))) = "1.25 moles S"#

Now, to find the number of atoms of sulfur present in this sample, use Avogadro's constant, which acts as the definition of a mole.

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

This means that your sample will contain

$1.25 \textcolor{red}{\cancel{\textcolor{b l a c k}{\text{moles S"))) * (6.022 * 10^(23)color(white)(.)"atoms S")/(1color(red)(cancel(color(black)("mole S")))) = color(darkgreen)(ul(color(black)(7.5 * 10^(23)color(white)(.)"atoms S}}}}$

I'll leave the answer rounded to two sig figs, but keep in mind that you only have one significant figure for the mass of sulfur.