Question

Complete combustion of 7.80 g of a hydrocarbon produced 24.9 g of CO2 and 8.93 g of H2O. What is the empirical formula for the hydrocarbon?

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

= 24.9/44

= 0.566

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

= 8.93/18

= 0.496

Since 1 mol of CO2 has 1 mol of C

Number of moles of C in CO2= 0.565909

so, x = 0.566

Since 1 mol of H2O has 2 mol of H

Number of moles of H = 2*0.496 = 0.992

Divide by smallest to get simplest whole number ratio:

C: 0.566/0.566 = 1

H: 0.992/0.566 = 1.75 = 7/4

multiply both by 4:

C : 1*4 = 4

H : 1.75*4 = 7

So empirical formula is:C4H7