How many molecules of carbon monoxide (co) are needed to react with excess iron (iii) oxide (fe2o3) to produce 11.6 g of iron (fe)?

8.73 grams CO
   The balanced equation for the reaction is
3CO + Fe2O3 ==> 2Fe + 3CO2
   So for every 2 atoms of Fe produced, 3 molecules of CO is needed. So let's start by looking up the atomic weights of the involved elements:
 Atomic weight iron = 55.845
  Atomic weight carbon = 12.0107 
  Atomic weight oxygen = 15.999
   Molar mass CO = 12.0107 + 15.999 = 28.0097 g/mol
 Moles iron = 11.6 g / 55.845 g/mol = 0.20771779 mol
   Moles CO needed = 0.20771779 mol / 2 * 3 = 0.311576685 mol
 Mass CO needed = 0.311576685 mol * 28.0097 g/mol = 8.727169487 g Rounding to 3 significant figures gives 8.73 grams CO

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