Question #6effe

For starters, you know that every mole of glycerol contains

• three moles of carbon, `3 xx "C"`
• eight moles of hydrogen, `8 xx "H"`
• three moles of oxygen, `3 xx "O"`

This means that your sample contains

`0.050 color(red)(cancel(color(black)("moles C"_3"H"_8"O"_3))) * "8 moles H"/(1color(red)(cancel(color(black)("mole C"_3"H"_8"O"_3)))) = "0.40 moles H"`

Now, in order to find the number of atoms of hydrogen, use the fact that every mole of elemental hydrogen contains `6.022 * 10^(23)` atoms of hydrogen, as given by Avogadro's constant.

This means that your sample contains

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

The answer is rounded to two sig figs, the number of sig figs you have for the number of moles of glycerol.

First we use Avogadro’s number to find out how many individual molecules there are. Then we multiply that value by the number of hydrogen atoms in the molecule.

`0.050mol * 6.022 xx 10^23 ("units"/"mol") = 3.011 xx 10^22` molecules

`3.011 xx 10^22 "molecules" * 8 ((H "atom")/"molecule") = 2.41 xx 10^23` hydrogen atoms