posted by Mark on .
A 0.5595 g sample of a compound containing C, H, and O was burned to produce 1.429 g CO2 and 0.5850 g H2O. If the molar mass of the compound was determined to be approximately 86.13 g/mol, what is its molecular formula?
I assume that's a pure compound.
Convert 1.429g CO2 to g C. The easy way is 1.429 x (atomic mass/molar mass CO2).
Convert 0.5850 g H2O to g H. That will be 0.5850 x (2*atomic mass H/molar mass H2O).
Then g O = mass compound - g C - g H.
Now convert g C to moles. mol = g/molar mass
Convert g H to moles.
Convert g O to moles.
Now find the ratio of the elements to each other with the smallest number being 1.00. The easy way to do that is to divide the smallest number of moles by itself (thereby assuring 1.00 for that), then divide all of the other numbers by the same small number. Round to whole number. (Note: don't round more than about 0.15 or so; i.e., 9.15 might be rounded to 9.0 BUI 9.25 would not). That will produce the empirical formula.
Now find the empirical formula mass, divide into 86.13, round to a whole number, then multiply that whole number by each of the subscripts in the empirical formula. Post your work if you get stuck.