text: can you solve this chemistry question? 1.00 g of unknown c contains 0.817 g carbon.  the complete combustion of 1.00 mol of unknown c requires 5 mol of o2.  what is the most likely molecular formula of unknown c? propane c3h8 + 5o2 ---> 3co2 + 4h2o  to work this out, assume compound is a hydrocarbon; atomic ratio is found by dividing % by atomic wt... c= 81.7/12 = 6.808 h= 18.3/1.008 = 18.15 a ratio h/c of 18.15/6.808 = 2.666/1 or 8/3 in whole numbers...thus  c3h8  success!...had this simple try not worked out, some combo containing o, n or other atoms would have been necessary.