How do I calculate the mass in grams for each of the following?

Hi! I need to calculate the mass in grams of each of the following: 6.03×10^20 H2O2 molecules, 6.0×1025 O3 molecules, and 9.88×1019 CH4 molecules. If someone could explain to me how to do this it would be greatly appreciated. Thank you in advance!

1 Answer
Apr 16, 2018

I'll go through it below.


Let's start with the mole and avagadro's number. Simplistically, the mole is a simple way to count LOTS and LOTS of "particles" (atoms, molecules, ions, compounds...whatever).

We can go back to carbon and say; "Right, so if you take 12.0 grams of Carbon-12 (the isotope), then you've got 1 mole of carbon, and that is #6.02xx10^23# atoms of Carbon.

So, 1 mole of anything is #6.02xx10^23# of those "anythings".

And on the periodic table, the mass of #6.02xx10^23# of each element is that elements molar mass (or said another way, 1 mole of the atoms on the periodic table weigh the molar mass). It is actually in the name, molar mass - the mass of 1 mole.

Anyway, from molecules - to moles - to atoms.

#("number of molecules")xx("1 mole"/(6.02xx10^23 "molecules"))xx("grams"/"mole" Molar Mass)#

#H_2O_2# is 34g/mole
#(6.03xx10^20 "molecules")xx("1 mole"/(6.02xx10^23 "molecules"))xx("34g"/"mole") = 0.034 g H_2O_2#

It is the exact same setup for the others - but with different molar masses and different numbers of molecules to start.