Question

You take an aspirin tablet (a compound consisting solely of carbon, hydrogen, and oxygen) with a mass of 1.00 g, combust it under an oxygen atmosphere, and collect 2.20 g of carbon dioxide and 0.400 g water. The molar mass of aspirin is between 170 and 190 g/mol. The molecular formula of aspirin is

Answer 1

g C = 2.20g CO2 x (atomic mass C/molar mass CO2) = about 0.6g

g H = 0.4g H2O x (2 atomic mass H/molar mass H2O) = 0.044

g O = 1.00g - g C - g H
Note: you need to redo all of this more accurately than I've done them.
Convert to mols
mols C = 0.6/12 = about 0.05
mols H = 0.044/1 = about 0.044
mols O = 0.356/16 = about 0.0222

Now find the ratio. The easy way is to divide by the smallest number.
0.044/0.0222 = 2 = H
0.05/0.0222 = 2.25 = C
0.0222/0.0222 = 1.0 = O
You can't round these to whole numbers BUT you can muliply by 1, 2, 3, 4, etc until you get whole numbers.
Try it and you will find multiply by4 gives H = 2*4 = 8
C = 2.25*4 = 9
O = 1*4 = 4
C9H8O4 should be the empirical formula.
Empirical formula mass is
(9*12) + (8*1) + (4*16) = 180
That falls withing the 170-190 range given in the problem therefore, there is only one grouping of C9H8O4 per molecule. The empirical formula is the same as the molecular formula.

Answer 2

Good!

Answer 3

You take an aspirin tablet (a compound consisting solely of carbon, hydrogen, and oxygen) with a mass of 1.00 g, burn it in air, and collect 2.20 g of carbon dioxide and 0.400 g water. The molar mass of aspirin is between 170 and 190 g/mol. The molecular formula of aspirin is