# Question c8c79

Oct 12, 2015

$15 \cdot {20}^{23} \text{atoms}$

#### Explanation:

The first thing you need to determine is how many atoms you get per molecule of hydrogen sulfide, $\text{H"_2"S}$.

You know by looking at the subscripts in the chemical formula that one molecule of hydrogen sulfide contains

• two atoms of hydrogen
• one atom of sulfur

So one molecule contains a total of three atoms.

Next, find you how many molecules of hydrogen sulfide you get in that many moles. You know that one mole of a substance contains exactly $6.022 \cdot {10}^{23}$ molecules of that substance - this is known as Avogadro's number.

In your case, you will have

0.8color(red)(cancel(color(black)("moles H"_2"S"))) * (6.022 * 10^(23)"molecules")/(1color(red)(cancel(color(black)("mole H"_2"S")))) = 4.818 * 10^(23)"molecules"

This means that the number of atoms will be

4.818 * 10^(23)color(red)(cancel(color(black)("molecules H"_2"S"))) * "3 atoms"/(1color(red)(cancel(color(black)("molecule H"_2"S")))) = 15.45 * 10^(23)"atoms"#

I'll leave the answer rounded to two sig figs, despite the fact that you only gave one sig fig for the number of moles of hydrogen sulfide

$\text{no. of atoms} = \textcolor{g r e e n}{15 \cdot {10}^{23}}$