Experiment 8: (Optional)

Chemical Hand Warmer

Oxidation of a Metal

Objective:

The objective of this lab is to observe the heat energy that is given off during the oxidation of iron.

Review of Scientific Principles:

When a reaction is endothermic (absorbs energy - heat) in one direction, such as the reduction of iron oxide to elemental iron, it will be exothermic (give off energy) in the reverse direction, the oxidation of elemental iron back to iron oxide.

Applications:

The converting of iron ore (iron oxide) in the blast furnace requires tremendous amounts of heat energy. When iron spontaneously oxidizes back to iron oxide (rust) in the air the heat released is not noticeable. When this reaction is sped up, the amount of heat is noticeable and usable in the form of a hand-warmer.

Time: 20 minutes

Materials and Supplies:

25 g Iron powder

1 g sodium chloride

1 Tbs. small vermiculite (might try sand)

plastic baggy

General Safety Guidelines:

• Avoid burns from the warm chemicals.

• Use normal precautions for a laboratory experiment.

Procedure:

1. Mass 25 g of iron powder or very fine iron filings and 1 g of sodium chloride. Place these in a small plastic bag. Shake the bag to mix.

2. Add about a tablespoon of vermiculite to the bag and shake well.

3. Add 5 ml of water and seal the bag. Shake it. The reaction will start after about a minute.

Questions:

1. The individual commercial sporting goods store hand warmers are purchased in a plastic bag. Inside the plastic bag is a cloth bag. The directions state that the plastic bags should not be removed until you are ready to activate the hand warmer. Why should the plastic bag not be removed?

2. In this reaction, iron metal was oxidized to form iron (III) oxide and heat was released. Mills that reduce ores to metals take a large amount of energy to form metals. Explain why the second process requires so much energy.

Teacher Notes:

• You might want to bring in a commercial hand warmer to show the students.

Answers to Questions:

1. The plastic bag keeps humidity (moisture) away from the chemicals until they are ready to be activated.

2. The reaction to form elemental iron from iron (III) oxide is very endothermic.