3) how to work out chemical formulae:
What is the simplest formula of a hydrocarbon that contains 60g of carbons combined with 20g of hydrogen?
(RAMS = H=1 C= 12)
Write mass of each element C= 60 H = 20
work out moles using formula
find simplest ratio (divide by smallest number) 5/5= 120/5=1
Write the formula showing the ratio of atoms CH4 (LOL)

4) Moles of molecule
just add all the RAM masses together
e.g water = H2O (H=1, O= 16
The Relative Molecular Mass (RMM) = 1+1+16= 18

or

Carbon dioxide, CO2 (C=12, O=16)

The RMM = 12+16+16=44

('2' only applies to the oxgyen atom, coz theres 2 of them)

hope that helps, or has it just made u more confused??

wa alykum aslaam