Question

You do a combustion analysis of an unknown solid (mass 95.98g) containing C,H, and O following the reaction: [CxHyOz + O2 >>> CO2 + H2O]. You are able to measure a mass of 95.85g of H2O and 188g of CO2. Find the molecular formula of the compound: CxHyOz. The molecular weight was found to be 135.183amu. Any help with this would be greatly appreciated!!!! Thanks

Answer 1

moles of CO2 = 188 / 44 = 4.273

moles of C= 4.273

mass of Carbon = 12 x 4.273 = 51.27 g

moles of H2O = 95.85 / 18 = 5.325

moles of H = 2 x 5.325 = 10.65 g

mass of hydroegen =10.65 g

Oxygen mass = 95.98 - (51.27 + 10.65 ) = 34.06 g

moles of O = 34.06 /16 = 2.129

C                O               H

4.272 2.129 10.65

2                 1 5

C2H5O -----------------------> empirical formula

empirical formula mass = 24+5 + 16 = 45

n = molar mass / empirical formula mass

    = 135.183 / 45

     = 3

molecular formula = n x empirical formula

                             = C6H15O3