Molar Mass Lab

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					Formula Weight of Iron Compound                       Name ____________________

Cautions: Wear eye protection
          Do not inhale the vapors of the reacting Iron fibers
          Hot things burn you, so do not touch the heated material — use tweezers.

1.     Find the mass of your crucible with the electronic balance on Mr. Samson’s desk.

       Mass of Crucible: __________________

2.     Obtain a sample of iron fiber (steel wool), put it in your crucible, and find the
       combined mass.

       Mass of Crucible + Iron: _____________         Mass of Iron: ______________

3.     Place the crucible of iron fiber on your ceramic triangle and begin heating it with
       your Bunsen burner.

       After two or three minutes of heating you should notice a color change spread
       across the surface of the iron sample. Extinguish the Bunsen burner and gently
       blow air through your straw onto your iron sample. You should notice that as you
       blow, the iron heats up as it reacts with the oxygen. Don’t blow too hard, or the
       sample will get too hot.

       Continue blowing air onto the sample until it stops glowing.

4.     You will have to wait at least ten minutes before you can transfer the crucible to
       the balance, otherwise it will be too hot, and it might damage you or the balance.

       While you are waiting for the sample to cool, determine the following:

       How many moles of Iron did you start with?                         _____________
       (show work)


       How many atoms of Iron did you start with?                         _____________
       (show work)


5.     When the iron reacted with oxygen, it could have formed either +2 or +3 ions.
       This means that the Iron and Oxygen combined to form either FeO or Fe2O3

       In order to find out which of these compounds formed, you need to determine the
       percent mass of Iron in each compound. To do this, divide the molar mass of the
       iron component of the compound by the molar mass of the compound itself.
      Percent Iron in FeO = Molar mass of Fe molar mass of FeO
      (show work)

                                              Percent Iron in FeO: ________________

      Percent Iron in Fe2O3 = Molar mass of Fe2  molar mass of Fe2O3
      (show work)

                                              Percent Iron in Fe2O3: ________________

6.    Calculate the predicted mass of both possible Iron Oxide compounds.

      Use the following equation to find the predicted mass:

      Predicted mass = starting mass  percent Iron

      Predicted mass if product is FeO: ________ (show work)


      Predicted mass if product is Fe2O3: ________ (show work)


7.    After the crucible has cooled, use your tweezers to take it over to the electronic
      balance and find the combined mass of the crucible and Iron Oxide compound.

      Mass of Crucible + Iron Oxide: _____________   Mass of Iron Oxide: ______________



8.    Compare the measured value of the Iron Oxide compound in #7 with the
      predicted values from #6.

      Which predicted value (FeO or Fe2O3) is closest to the measured value? ________

9.    Assuming that you are correct about which compound formed, calculate the
      percent error in your measured value by using the following equation:

      Percent error =  predicted mass – measured mass         100%
                              Predicted mass


                                                            Percent error: ___________

10.   How many moles of Iron Oxide did you end up with?


                                                     Moles of Iron Oxide: ____________

				
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posted:12/4/2011
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