Complete combustion of 4.00 g of a hydrocarbon produced 12.3 g of CO2 and 5.68 g of H2O. What is the empirical formula for the hydrocarbon? Insert subscripts as necessary.

Answer 1

C_xH_y + O₂ → CO₂ + H₂O

All of the C from the hydrocarbon is found in the CO₂ while all of the H is in the water. Calculate the mass of C and H in the products:

(12 g C/44 g CO₂) x 12.3 g CO₂ = 3.36 g C

(2 g H/18 g H₂O) x 5.68 g H₂O = 6.31 g H

Next, calculate the moles of C & H represented by these masses:

(1 n C/12 g C) x 3.36 g C = 0.280 n C

(1 n H/1.10 g H) x 6.31 g H = 0.624 n H

Dividing by the smaller value (i.e. 0.280) we get a 1:2 ratio. Therefore, the empirical formula would be CH₂