5.
3.
Formula Weight of Iron Compound
Cautions: Wear eye protection
Name ____________________
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.
2.
Mass of Crucible: __________________
Obtain a sample of iron fiber (steel wool), put it in your crucible, and find the combined mass.
Mass of Crucible + Iron: _____________
Place the crucible of iron fiber on your ceramic triangle and begin heating it with your Bunsen burner.
Mass of Iron: ______________
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)
_____________
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 Fe
2
O
3
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 Fe
2
O
3
= Molar mass of Fe
2

molar mass of Fe
2
O
3
(show work)
Percent Iron in Fe
2
O
3
: ________________
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 Fe
2
O
3
: ________ (show work)
7.
8.
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: ______________
Compare the measured value of the Iron Oxide compound in #7 with the predicted values from #6.
Which predicted value (FeO or Fe
2
O
3
) 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
Predicted mass
 
100%
Percent error: ___________
10. How many moles of Iron Oxide did you end up with?
Moles of Iron Oxide: ____________