Question

Azulene is a beautiful blue hydrocarbon consisting of only C and H atoms. If 0.106 g of the compound is burned in oxygen, 0.364 g of CO₂ and 0.0596 g of H₂O are made. Determine the empirical formula of azulene from this data. [ Hint: First convert the masses of CO₂ and H₂O to moles, then convert the moles found to moles of C to H. ]

Answer 1

C%   = 12*wt of CO2*100/44*wt of compound

            = 12*0.364*100/44*0.106   = 93.65%

H%     = 2*wt of H2O *100/18*wt of compound

             = 2*0.0596*100/18*0.106    = 6.25%

Element                 %                 A.wt            no of moles                simple ratio              simplest ratio

C                        93.65              12                93.65/12   = 7.8                      7.8/6.25   = 1.248        1.248*4 = 5

H                        6.25                  1                 6.25/1       = 6.25                   6.25/6.25 = 1               1*4       = 4

The empirical formula of Azulene = C5H4