Question

Complete combustion of 8.40 g of a hydrocarbon produced 25.4 g of CO2 and 13.0 g of H2O. What is the empirical formula for the hydrocarbon?

Answer 1

25 g of CO2 contain C = 12 * 25/44 = 6.818 g    ( = (atimic weight of C /molecular weight of CO2 ) * weight of CO2

13 g of H2O contain H = 2/18 *13 = 1.444 g    ( = weight of H / molecular weight of water) * weight of H2O

Moles of C in 6.818 g = 6.818/12 = ).568       (=weight of C/atomic weight of C)

"            H in 1.444 g of H = 1.444/1 = 1.444   (=weight of H/ atomic weight of H

So mole ratio =C:H

                  = .568 : 1.444

                   = .568/.568 : 1.444/.568

                   = 1: 2.54

                   = 2:5 (round figure )

So empirical formula of hydrocarbon = CH5