Overview.

    Iron(III) oxide is an ocher red powdery solid that is known as the mineral haematite (hematite in USA) and is the principal component of most iron ore.  It is also used as a pigment and as a polishing agent called jewelers’ rouge.

    Fe2O3 can be used to demonstrate both physical and chemical changes. Upon heating Fe2O3 with a burner flame, the solid turns into a dark brown-black solid variation of Fe2O3.  This form reverts back to the original color upon cooling to room temperature.  Neither form is attracted to a magnet.

    When heated, Fe2O3 reacts with hydrogen to form metallic iron according to the reaction:

    In this article, we describe this reaction as a microscale experiment suitable for high school and college students.  The reaction takes place in a glass pipette and uses less than 0.25 g Fe2O3 and 50-mL H2(g). The metallic iron that results is attracted to a magnet and demonstrates that nearly complete conversion has taken place.  The other product, H2O, is detected as droplets inside the pipette stem.  This experiment demonstrates both physical and chemical changes and costs less than $0.15 per pair of students and can be completed within a 40-minute laboratory period.  A similar reaction can be performed as a large scale demonstration as shown in the video series “World of Chemistry.” ²

Before any heating takes place, Fe2O3 is not attracted to the magnet.

The magnet shows that most of the Fe2O3 has been converted into metallic iron.

    As an optional continuation of this experiment, the elemental iron produced in the pipette can be reacted with oxygen to form Fe2O3 again:

Chemicals and materials needed:³

• (2) 60-mL plastic syringes
• Latex syringe caps
• 2-cm lengths of Latex tubing, 1/8-inch (3.175 mm) ID
• small Bunsen burner
• glass Pasteur pipette
• magnet
• wooden stick such as a kabob skewer to tamp the steel wool into the pipette
• ring stand and clamp
• Silicone oil or spray
• Fe2O3, 0.25 g
• hydrogen (5 mL 2 M HCl, 0.1 g Mg ribbon, powder or turnings)
• ‘000’ steel wool, 0.1 g
• Optional: oxygen (5 mL 3 - 6% H2O2, 0.1 g KI )

Construction
     Use a wooden stick to tamp a small plug of steel wool into the constricted portion of a glass Pasteur pipette as shown in Figure 1.  Add 0.25 g powdered Fe2O3 to the pipette.  While holding the pipette in a horizontal position, tap the pipette with your finger near the steel wool plug until most of the Fe2O3 has accumulated in a mound as shown in Figure 1.  Position the pipette horizontally using a clamp and ring stand.  Fasten the clamp near the end with the latex tubing.

General Safety Precautions.
    Always wear safety glasses.  Gases in syringes may be under pressure and could spray liquid chemicals.  Follow the instructions and only use the quantities suggested.

Suitability.
    This laboratory activity is suited for high school and university-level chemistry students.

Syringe Lubrication.
    We recommend lubricating the black rubber diaphragm of the plunger with silicone spray (available from hardware stores) or medium-grade silicone oil (Educational Innovations Number GAS-150)

Preparation of Hydrogen:
    Prepare a syringeful of hydrogen from 0.1 g Mg (powder, ribbon or turnings) and 3 - 5 mL 2 M HCl(g).  Detailed instructions can be found at our website⁴ or in our two microscale gas books.^{5, 6}

Instructions:
Part 1.  Hold a magnet above the mound of Fe2O3 inside the pipette. The compound is not magnetic so nothing should happen.  Heat the mound of Fe2O3 with the flame of a Bunsen burner.  Within a few seconds the color of the solid will darken.  Remove the flame and again hold the magnet above the dark Fe2O3.  This variation is also non-magnetic.⁷  Allow the pipette to cool for 5 minutes and the original color and form of Fe2O3 will return.

Part 2.  Connect the H2-filled syringe to the pipette using a short length of latex tubing.  Heat the Fe2O3 again and then slowly pass the hydrogen gas through the pipette.  The powder will quickly darken.  Water droplets should appear inside the stem of the pipette.  After all of the hydrogen has been passed through the pipette, remove the heat and allow the pipette to cool.  Holding a magnet above the mound of solid will attract the metallic powdered iron to the top of the pipette (the third color photograph in the sequence above).

Part 3.  (Optional) Prepare a syringeful of oxygen.  (Air can be used instead of oxygen, but the results are not as good.)  Heat the iron powder in the flame until it is hot.  Slowly pass a syringe of oxygen through the pipette while heating. The iron will glow brightly white as it reacts with the oxygen.  Remove the heat and allow the pipette to cool to room temperature.  Hold the magnet in position above the pipette.  Much of the iron should have been oxidized back to Fe2O3 and is non-magnetic.  The oxidation is not as efficient as the reduction in Part 2, so some metallic iron usually remains.
 

Clean-up and Storage.
    At the end of the experiments, clean all syringe parts (including the diaphragm), caps and tubing with soap and water.  Rinse all parts with distilled water.  Be careful with the small parts because they can easily be lost down the drain. Important: Store plunger out of barrel.  The pipettes filled with Fe and Fe2O3 may be safely discarded in the trash.

Laboratory Report Sheet
Part 1.

Length of time sample was heated before it turned dark:
Observations for the initial heating of Fe2O3:
Results of magnet test:

Volume of hydrogen passed through the pipette (over the Fe2O3):
Time it took to pass the hydrogen through the pipette:
Observations for the reaction between Fe2O3 and H2:
Results of magnet test:

Volume of oxygen passed through the pipette (over the iron):
Time it took to pass the oxygen through the pipette:
Observations for the reaction between Fe(s) and O2:
Results of magnet test:

Laboratory Report Questions.

1. Balance the equation for the reaction between Fe2O3 and H2.
2. Calculate the rate of hydrogen flow in mL/min.
3. Why is it necessary to heat the Fe2O3 in order for it to react?
4. Substances that are attracted to a magnet are called ferromagnetic.  Is Fe2O3 ferromagnetic?  Is Fe?
5. Calculate the number of moles of Fe2O3 used in the pipette.  Calculate the number of moles of H2 passed through the pipette.  Which reagent was in excess?
6. As the reaction between oxygen and iron took place, a bright white glow may have been observed.  Does this indicate an exothermic or endothermic reaction?

Endnotes:
1 Author to whom correspondence should be addressed.  E-mail: xenon@creighton.edu
2 The syringe and related equipment can be ordered from a variety of vendors including Educational Innovations, Flinn Scientific (US sales only), S17 Science Supplies, Micromole, Fisher Scientific, etc.  Part numbers and links to their websites are provided at our microscale gas website (Endnote 3)
3 Website:  http://mattson.creighton.edu/Microscale_Gas_Chemistry.html
4 The Chemistry of Gases, A Microscale Approach, Mattson, B. M., Anderson, M. P., Schwennsen, Cece, Flinn Scientific, 1999, ISBN #1-877991-54-6.
5 Microscale Gas Chemistry, Mattson, B. M., Educational Innovations, 2000, ISBN #0-9701077-0-6.
6 Fe2O3 has a fairly complex solid-state chemistry.  Under normal conditions it exists in a form called a-Fe2O3.  At temperatures above 400 ? 700 ^oC (references vary), it converts to a ferromagnetic form called g-Fe2O3.  The temperature inside the pipette when we see Fe2O3 darken is no more than 140 ^oC.  Although we are far from certain, it is known that crystal defects can lead to color changes when heated.