ANOTHER AP chem ch 3 question?

Question

please solve and explain how to solve:
Ibuprofen is made up of carbon, hydrogen, and oxygen. when a sample of ibuprofen wighing 5.000 g burns in oxygen, 13.86 g of CO2 and 3.926 g of water are obtained. waht is the simplest formula of ibuprofen?

Answer 1

*Notice* my calculations are simplified and done in my head, redo them for your homework

Simplified:
C burns with O2 to make CO2 (C + O2 -> CO2)
H burns with O2 to make H2O (2H + 0.5 O2 -> H2O)

Molecular weights of:
C = 12 g/mol
O = 16 g/mol
H = 1 g/mol
CO2 = 44 g/mol
H2O = 18 g/mol

So, 13.86 g of CO2 is 13.86 g / 44 g/mol = .32 mol CO2 = .32 mol C
3.926 g of H2O is 3.926 g / 18 g/mol = .22 mol H2O = .11 mol H (2 H's are used for each mol of H2O)

You don't know the amount of oxygen in the sample, since O2 was available from the atmosphere during the burning, so you need to find the weights of C and H to determine the amount of O.
.32 mol C = .32 mol * 12 g/mol = 3.8 g C
.11 mol H = .11 mol * 1 g/mol = 0.11 g H
5.000 g Ibuprofen - 3.8 g C - 0.11 g H = 1.1 g O

1.1 g O / 16 g/mol = 0.069 mol O

So, is 5.000 g Ibuprofen, there are 0.32 mol of C, 0.11 mol of H and 0.069 mol O

That makes the empirical formula C0.32 H0.11 O0.069.

Factor it: C23 H8 O5

Like I said, this is approximate, but it should show you how to do it, and your result should be close to mine.

Answer 2

13.86g CO2 requires 13.86*12/44=3.780g C 3.78/12=.315 moles
3.926g H2O requires 3.926*2/18=.436g H .436/1=.436 moles
5.000-3.780-.436=.784g O .784/16= .049 moles

total moles: .315+.436+.049=.8
mole fractions:
.315/.8=.394 C
.436/.8=.545 H
.049/.8=.061 O

empirical formula is C13H18O2

Answer 3

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