Question

If a 16.00 g sample of methane has 12.00 g of Carbon and 4.00 g of Hydrogen, why is the chemical formula CH4? Since it's a 3:1 mass ratio, shouldn't it be C3H?

Answer 1

while it's ratio is that, the elements themselves don't weigh the same

Answer 2

12 g of Carbon is one mole
1g of Hydrogen is one mole

Answer 3

oh, we haven't covered the mole yet, so how do you set that up as an equation?

Answer 4

a mole is an amount, like a dozen

1 dozen of atoms = 12 atoms
1 mole of atoms = 6.023x10^23 (called avogadros number)

in stoichiometry, atoms react in terms of moles not grams..

n=m/MW ... ie. moles equal mass over molecular weight

MW is the value you find on the periodic table which is equivalent to the mass of one mole of atoms of that element

the problem:
basically divide each element by it's MW, and you'll end up with C=1 and H=4

C:H
1:4