Question

Complete combustion of 4.00 g of a hydrocarbon produced 12.1 g of CO2 and 6.20 g of H2O. What is the empirical formula for the hydrocarbon?

__CH__

(insert subscripts as necessary)

Answer 1

let in compound number of moles of C and H be x and y respectively

Number of moles of CO2 = mass of CO2 / molar mass CO2

= 12.1/44

= 0.275

Number of moles of H2O = mass of H2O / molar mass H2O

= 6.2/18

= 0.3444

Since 1 mol of CO2 has 1 mol of C

Number of moles of C in CO2= 0.275

so, x = 0.275

Since 1 mol of H2O has 2 mol of H

Number of moles of H = 2*0.3444 = 0.6889

Divide by smallest:

C: 0.275/0.275 = 1

H: 0.6889/0.275 = 2.50

multiply by 2 to get simplest whole number ratio:

C : 1*2 = 2

H : 2.50*2 = 5

So empirical formula is:C2H5