Question

How many molecules are in 3 moles of `H_2S`?

Answer 1

`1.8 * 10^(24)"molecules"`

Explanation:

As you know, a mole is simply a very, very large collection of molecules.

In order to have one mole of a molecular substance, you need to have `6.022 * 10^(23)` molecules of that substance `->` this is known as Avogadro's number and it can be used as a conversion factor to go from number of molecules to moles and vice versa.

`color(blue)(|bar(ul(color(white)(a/a)"1 mole" = 6.022 * 10^(23)"molecules"color(white)(a/a)|)))`

Now, you want to know how many molecules are present in `3` moles of hydrogen sulfide, `"H"_2"S"`.

According to Avogadro's number, `1` mole of hydrogen sulfide contains `6.022 * 10^(23)` molecules of hydrogen sulfide, which means that `2` moles will contain

`3 color(red)(cancel(color(black)("moles H"_2"S"))) * overbrace((6.022 * 10^(23)"molecules H"_2"S")/(1color(red)(cancel(color(black)("mole H"_2"S")))))^(color(blue)("Avogadro's number")) = color(green)(|bar(ul(color(white)(a/a)color(black)(1.8 * 10^(24)"molecules H"_2"S")color(white)(a/a)|)))`

I'll leave the answer rounded to two sig figs.