Find the mass of carbon in propane given the mass of propane(C3H8) is 1kg?

Question

How do you find out the mass of the carbon? Can someone write out the steps to do it please? I'm not sure what to do when it comes to finding the mass of carob because I'm not sure whether to use the molar mass of carbon or the MM(carbon) times 3?

Answer 1

It's been a while since I did chemistry but I think one of those numbers on the periodic table is the atom's mass. Once you know the mass of a Carbon and a Hydrogen atom you can work it out fairly easily.

(Mass of Carbon x 3) + (Mass of Hydrogen x 8) = Mass of propane molecule.

1000g (1KG in grams) / Mass of propane (in grams) = Number of propane molecules

(Mass of Carbon x 3) x Number of propane molecules = Mass of Carbon in 1KG of propane.

There might be an even easier way, but I'm tired and I failed Maths.

EDIT: Actually I didn't even know what you mean by molar mass, so it's probably a good idea to ignore me.

Answer 2

Each molecule of propane is made up of 3 Carbon atoms and 8 Hydrogen atoms. One carbon atom weighs 12 amu, while one hydrogen atom weighs around 1 amu (these can be found on the periodic table, and roughly correspond to the atomic number for most elements).

So, the mass of one molecule of propane is:

3*12 amu (for the 3 Carbons) + 8*1 amu (for the 8 hydrogens) = 44 amu

Out of that total mass, 36 amu is all made up of carbon, meaning about 82%. This ratio holds for any amount of propane, so 1kg (1000 g) would yield (.82*1) = .82 Kg or 820 g of carbon.

I believe that 1 amu is equal to a gram divided by a mole, so the molar mass of carbon would be 12 g, whereas the atomic mass is 12 amu.