[kep1]

The question is...
The elements contained in acetylsalicylic acid are hydrogen, carbon, and oxygen. The combustion of 3.000g of pure compound yields 1.200g of water and 6.600g of dry carbon dioxide. Determine the mass, in grams, of each element (H,C, & O) in the 3.000g sample of the compound.

Ok so we have C9H8O4 + 02 -> CO2 + H20 which needs to be balanced correct? So that would be C9H8O4 + 9O2 -> 9CO2 + 4H20 right?
Next, do I need to convert 3g of C9H8O4 to moles of C9H8O4? The molecular weight of that is 180g so 3/180 = .0167m C9H8O4 right?
If this is all right so far then I need to convert moles of my compound to moles of each element and then moles of each element to grams of each element correct? Well, I am stuck converting from moles of C9H8O4 to moles of each element. Can someone explain that part please? Thanks in advance.

[Borek]

You don't need acetylsalicylic acid formula for calculations. Calculate mass of the carbon in carbon dioxide, calculate mass of the hydrogen in water. Whatever is left (ie C+H doesn't add to 3.000 g) must be oxygen.

[kep1]

hmm okay so 1m of H2O = 18g. H in 1m of H2O = 2/18 or 1/9 so 1.2g * (1/9) = .1333g of H.
1m of CO2 = 44g. C in CO2 = 12/44 or .2727 so 6.6g * .2727 = 1.800g of C.
3 - (.1333 + 1.800) = 1.067g of O.

is this correct? thanks for your reply btw.

[Borek]

hmm okay so 1m of H2O = 18g. H in 1m of H2O = 2/18 or 1/9 so 1.2g * (1/9) = .1333g of H.
1m of CO2 = 44g. C in CO2 = 12/44 or .2727 so 6.6g * .2727 = 1.800g of C.
3 - (.1333 + 1.800) = 1.067g of O.

is this correct? thanks for your reply btw.

OK

I am stuck converting from moles of C9H8O4 to moles of each element.

Now, as you see it wasn't necessary, but this conversion is pretty easy. Mole is just an overgrown dozen. If you have dozen molecules, and each have 9 carbon atoms, there is nine dozens of carbon atoms. Now, if you have a mole of molecules, how many moles of carbons atoms do you have?