Question

Complete combustion of 4.40 g of a hydrocarbon produced 14.1 g of co2 and 5.04 g of h2o. what is the empirical formula for the hydrocarbon?

Answer 1

For a hydrocarbon, the combustion reactions are the following:

C + O₂ --> CO₂
H₂ + 1/2 O₂ --> H₂O

The molar mass of CO₂ is 44 g/mol while C is 12 g/mol. Let's solve for amount of C in hydrocarbon.

Mass of C = (14.1 g CO₂)(1mol/44g)(1 mol C/1 mol CO₂)(12 g/mol) = 3.845 g C
So, that means that the mass of hydrogen is:
Mass of H = 4.4 - 3.845 = 0.555 g

Moles C = 3.845/12 = 0.32042
Moles H = 0.555/1 = 0.555
Divide both by the smaller value, 0.32042.

C: 0.32042/0.32042 = 1
H: 0.555/0.32042 = 1.732
We have to get an answer that is closest to a whole number. Let's try multiplying both with 4.
C: 1*4 = 4
H: 1.732*4 = 6.93≈7

Thus, the empirical formula is C₄H₇.