Question

When 0.500g sample of an organic material composed of carbon, hydrogen and oxygen was burned, it produced 0.6871g CO2 and 0.1874g H2O. The MW of the compound 192. What is the empirical formula and the molecular formula of the sample?

check below!

Answer 1

hi, i've been stuck with this question for 9 days now.. this is the solution that i managed. but i think it's wrong. can someone please correct me?

Answer 2

I would recommend always writing units after numbers in your calculations. It helps prevent confusion and makes it clear what you’re working with.

You correctly converted 0.6871g CO2 and 0.1874g H2O to moles C and moles H. You correctly calculated grams of oxygen. However, at the next step you’re trying to divide grams of each element by the moles of each element. This will *not* give you the molar ratio.

To get the molar ratio, convert 0.292g O to moles. Find the lowest molar amount between moles C, moles H, and moles O. Divide all three molar quantities by the lowest molar amount. The results will be the ratio between C H and O.

Answer 3

I’m actually getting weird numbers for this problem so I’ll try to revisit my calculations in a bit

Answer 4

Also something to keep in mind, the molecular formula will always be a whole number multiple of the empirical formula (all the subscripts from the empirical formula should be multiplied by some constant integer to get the molecular formula). So right off the bat I can see something’s up with your molecular formula too.

Answer 5

See attached. I put a star by the molar ratio section because I think that’s where you’re getting confused.

For this problem, notice how the empirical formula gives us a compound with MW 192g/mol. This matches the MW given in the problem. So for this compound, the molecular formula is actually the same as the empirical formula.