Question #1e5b3

The first thing that you need to do here is to convert the mass of water to moles by using the compound's molar mass.

`36 color(red)(cancel(color(black)("g"))) * ("1 mole H"_2"O")/(18.015color(red)(cancel(color(black)("g")))) = "1.998 moles H"_2"O"`

Now, you know that very mole of water contains

• two moles of hydrogen, `2 xx "H"`
• one mole of oxygen, `1 xx "O"`

This means that your sample contains

`1.998 color(red)(cancel(color(black)("moles H"_2"O"))) * "2 moles O"/(1color(red)(cancel(color(black)("mole H"_2"O")))) = "3.996 moles O"`

Finally, to find the number of atoms of oxygen present in the sample, use the fact that `1` mole of elemental oxygen must contain `6.022 * 10^(23)` atoms of oxygen `->` this is the definition of a mole given by Avogadro's number.

You will end up with

`3.996 color(red)(cancel(color(black)("moles O"))) * (6.022 * 10^(23)color(white)(.)"atoms O")/(1color(red)(cancel(color(black)("mole O")))) = color(darkgreen)(ul(color(black)(2.4 * 10^(24)color(white)(.)"atoms O")))`

The answer is rounded to two sig figs.