How about this one?A dry-cleaning solvent (molecular weight = 146.99 g/mol) that contains C, H, and Cl is suspected to be a cancer-causing agent. When a 0.321 g sample was studied by combustion analysis, 0.576 g of CO2 and 0.0780 g of H2O formed.
How many moles of each of the following were in the original sample?
This is the approach I saw from another example:
0.576g CO2 x 12gC/44gCO2 = .15709g C
0.0780g H2O x 2gH/18g H2O = 0.008666g H
Remaining weight is due to Cl: 0.321 - 0.15709 - 0.008666 = 0.156333g
Convert to moles.
C = .15709g x 1mol/12g = 0.01309mol (this one I got correct)
H = 0.008666g x 1mol/1g = .008666 (wrong)
Cl = 0.156333g x 1mol/35.45g = 0.004409mol (wrong)
divide through by the lowest mole number to get the lowest empirical formula possible.
C = 0.01309/0.004409 = 3
H = .008666/0.004409 = 2
Cl = 0.004409/0.004409 = 1
It adds to a formula weight of 73.495g/mol.
molecular formula=C6H4Cl2 (this was right)