Question

A 14.60 g sample of an unknown compound, composed only of carbon, hydrogen, and oxygen, produced 28.6 g of CO, and 14.6 g of H,O in a combustion analysis. What is the mass percent composition of oxygen of the unknown compound? • Round to one decimal place. Provide your answer below:

Answer 1

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

= 28.6/44

= 0.65

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

= 14.6/18

= 0.8111

Since 1 mol of CO2 has 1 mol of C

Number of moles of C in CO2= 0.65

Since 1 mol of H2O has 2 mol of H

Number of moles of H = 2*0.8111 = 1.622

mass O = total mass - mass of C and H

= 14.6 - 0.65*12 - 1.622*1

= 5.178

Now use:

Mass % of O = mass of O * 100 / mass of sample

= 5.178 * 100 / 14.60

= 35.47 %

Answer: 35.47 %