text: a certain compound was found to have a molar mass of 32.042 g.? a   3.827 g   sample of this compound was burned in pure oxygen gas. the measured amount of   co2   produced was   5.256 g,   while that of   h2o   was   4.303 g.   no other products were produced in the reaction.  how many moles of   carbon   were in the original sample that underwent combustion ? gimme a minute...  first guess is 0.1195 moles of carbon.  how? since you got 5.256 g of co2, if you divide that with the molecular mass of co2 you'll get the moles of co2:  5.256 g x (1 mole of co2 / 44g of co2) = 0.1195 moles of co2  [  44 from c (12g/mole) and o2(2 x 16g/mole)  ]  from 0.1195 moles of co2 multiply that with (1 mole of carbon per 1 mole of carbon dioxide co2) which makes the number of moles of co2 = to the number of moles of carbon. not a single molecule of carbon is wasted, so i guess it's safe to assume that's also the number of moles of carbon in the reactants.