Question

Question #8c3c6

Answer 1

`1.81 * 10^(25)"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 * 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 * 10^(23)` molecules of that substance `->` this is known as Avogadro's constant.

`color(blue)(ul(color(black)("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 * 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 * 10^(25)` `"molecules H"_2"S"`

The answer is rounded to three sig figs.