a 1.295g sample of a hydrocarbon is burned in an excess of oxygen producing 3.553g of co2 and water .what mass of hydrogen is contained in the original sample

Answer 1

Assuming the combustion was complete, then all of the H in the hydrocarbon ends up in H₂O.

Using the law of conservation of matter, we can find the mass of H₂O produced and hence the mass of H in the original sample.

moles CO₂ = 3.553 g CO₂ x 1 mol CO₂ / 44 g = 0.08075 moles CO₂

mass of C = 0.08075 moles CO₂ x 1 mol C / mol CO₂ x 12 g C / mol = 0.969 g C

mass of H = 1.295 g - 0.969 g = 0.326 g H in original sample

------------------------------------------------------------------------------------------------------

extra credit:

moles H = 0.326 g x 1 mol H / 1 g = 0.326 mols H

moles C = 0.08075

Divide both by 0.08075 to try to get whole numbers of moles

0.08075 / 0.0875 = 1 mole C

0.326 /.08075 = 4.0 mole H

Empirical formula of unknown hydrocarbon is CH₄