How to solve this combustion analysis question

Combustion analysis of 1.00g of testosterone yields 2.90g of CO2 and .875g H2O. What are the mass percents of carbon, hydrogen, and oxygen?

Step 1, write a rough equation.

CxHyOz + O2--> xCO2 and y/2 H2O

So you see that moles of CO2 = moles of C in your compound

Moles of water = 1/2 moles of H in compound


Convert masses to moles of CO2 and H2O by dividing by molar masses ( 44 and 18)

mole CO2 = 0.0659 which contains 0.0659 moles of C
mole H2O =0.0486 which contains 0.0972 moles of H

For percent of C =( mass of C / mass of sample ) x 100%

(0.0659 x 12G)/1.00g x 100% = 79.08% carbon

do the same thing for the hydrogen %

Then for the oxygen - 100% - % carbon -% hydrogen/

Happy Studies.