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Question

a 1.367g sample of an organic compound was combusted in a stream of dry oxygen to yield 3.002g CO2 and 1.64g H2O. if the original compound contained only carbon, hydrogen, and oxygen, what is its empirical formula?

Answer 1

Let CxHyOz is the formula of the compound

CxHyOz_ +_ (4x+y-2z)/4 O2 ==> xCO2____+____ y/2 H2O

__3.367g___3.275g _________ 3.002g________ 1.64g

_________0.102moles______ 0.068moles ___0.091moles

==>0.068/x= 1.367/(12x+y+16z)

==>0.091*2/y=1.367/(12x+y+16z)

==> 4*0.102/(4x+y-2z)=1.367/(12x+y+16z)

Solve the system==>x,y,z

Answer 2

3.002 g CO2 contains 0.8193 g C atoms or 0.06821 mol C atoms

1.640 g H2O contains 0.1835 g H atoms or 0.18208 mol H atoms

1.367 g sample - 0.8193 g C - 0.1835 g H = 0.3642 g O atoms

0.3642 g O atoms = 0.02276 mole O atoms

Find the mole ratios for a compound with 1 O atom-

C: 0.06821 mol / 0.02276 mol = 3.0

H: 0.18208 mol / 0.02276 mol = 8.0

O: 0.02276 mol / 0.02276 mol = 1.0

empirical formula = C3H8O