posted by mark on .
I need help with this problem...
A 1.208 g sample of a compound containing C, H, and O was burned to produce 2.561 g CO2 and 0.3930 g H2O. Calculate the empirical formula of the compound.
I always get stuck when it comes to finding the subscript for this compound.
Convert 2.561g CO2 to g C. Easiest done by 2.561 x (atomic mass C/molar mass CO2).
Convert 0.3930g H2O to g hydrogen. Easiest done by 0.3930 x (2*atomic mass H/molar mass H2O).
Then g O = 1.208 - g C - g H
Now convert g C, H, and O to moles.
moles = grams/molar mass.
Find the ratio of the elements to each other using whole numbers with the smallest being 1.00. That is easiest done by dividing the smallest number by itself; then divide the other mole amounts by the same small number.
If you have trouble, post your work and I can help guide you through it. Be sure to explain what you don't understand about the next step.
I ended up with C_2.809 H_2.106 O_1
so would that be C_3 H_2 O?
I would round that way BUT I didn't get those numbers. I ended up with 1.99 for C, 1.496 for H, 1.00 for O which rounds to C2H1.5O but that in small whole numbers is C4H3O2 if I didn't make a math error. Look over your work to see if you can find an error; post your work and I'll look for an error if you wish.