# Question 8c3c6

Mar 31, 2017

$1.81 \cdot {10}^{25} \text{molecules H"_2"S}$

#### Explanation:

All you have to do here is to use the definition of a mole as a conversion factor to go from the number of moles of hydrogen sulfide to number of molecules.

As you know, we can use a mole to denote a very, very large collection of things. In this case, $1$ mole of hydrogen sulfide will contain $6.022 \cdot {10}^{23}$ molecules of hydrogen sulfide.

This is, in fact, the definition of a mole. In order to have one mole of any molecular substance, you need to have $6.022 \cdot {10}^{23}$ molecules of that substance $\to$ this is known as Avogadro's constant.

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

So, you know that $1$ mole of hydrogen sulfide will contain $6.022 \cdot {10}^{23}$ molecules of hydrogen sulfide. You can thus say that $30.0$ *moles will contain

30.0 color(red)(cancel(color(black)("moles H"_2"S"))) * (6.022 * 10^(23)color(white)(.)"molecules H"_2"S")/(1color(red)(cancel(color(black)("mole H"_2"S"))))#

$= 1.81 \cdot {10}^{25}$ $\text{molecules H"_2"S}$

The answer is rounded to three sig figs.