Mini-Mini Heater
SCIENTIFIC
Introduction
Illustrate the exothermic reaction of rusting iron.
Concepts
• Rust
• Oxidation of iron
Materials
Mini-Mini Heater
Safety Precautions
The heater is non-toxic but should not be consumed or come in contact with eyes. The maximum temperature reached by the heater is
about 69 °C (156 °F) and thus may cause burns. Precautions should be taken to prevent burns. Follow all laboratory safety guidelines.
Wash hands thoroughly with soap and water before leaving the laboratory.
Procedure
1. Remove the Mini-Mini Heater from the plastic wrapper. Observe the heater.
2. Gently squeeze the heater to activate it.
3. Feel the warmth given off. The heater will remain at a constant temperature of about 57 °C (135 °F) for seven hours or
more. Continued squeezing and open exposure to the air will decrease the life of the heater.
Disposal
Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures governing the disposal of laboratory waste. Dispose of Mini-Mini Heater in the trash according to Flinn Suggested Disposal
Method #26a when cold.
Discussion
The Mini-Mini Heater contains iron, water, cellulose, vermiculite, activated carbon, and salt. How can these simple ingredients produce such a large amount of heat for such a long time?
The answer is rust. The iron in the pouch, when exposed to the oxygen in the air, oxidizes and therefore produces rust.
Oxidation is the process in which a substance combines with oxygen. When iron oxidizes, it produces iron(III) oxide (ferric oxide) or more commonly, rust. A noticeable amount of heat is given off and thus the reaction is said to be exothermic.
During the last 2–6 hours, heat is still given off but in a lesser amount that may not be noticeable to the touch. The reaction for the oxidation of iron is shown on page 2. Notice that heat is considered a product of the reaction.
4Fe + 6H2O + 3O2 → 4Fe(OH)3 + Heat (96 Kcal/mole)
4Fe(OH)3 → 2Fe2O3 + 6H2O
4Fe + 3O2 → 2Fe2O3 + Heat
Why doesn’t the iron oxidize when in the plastic wrapper? What does squeezing the pouch do? The heater is initially in a
vacuum-sealed bag. When you open the wrapper, the iron is now exposed to atmospheric oxygen. The iron is in powdered
form which increases the surface area exposed to the oxygen and increases the rate of reaction. Squeezing the heater will
increase the amount of iron (or surface area) that is exposed to oxygen. Excessive squeezing of the heater will introduce
oxygen too quickly and will shorten the life of the heater.
The salt is added to speed up the oxidation process (act as a catalyst). Many of us, unfortunately, see this similar reaction on
our cars when the roads are salted in winter.
© 2016 Flinn Scientific, Inc. All Rights Reserved.
Publication No. 1931
061616
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Mini-Mini Heater continued
The purpose of the carbon is to absorb oxygen from the air. Vermiculite, which is often used as an insulator, is added for that
same purpose here to retain heat. Cellulose, the fundamental constituent in wood, grass, cotton, and all vegetable tissue, is
added to retain the water and keep the heater dry to the touch.
Acknowledgment
Jack Shonba, Lyons Township High School, Western Springs, IL.
The Mini-Mini Heater is available from Flinn Scientific, Inc.
Catalog No.
AP1931
Description
Mini-Mini Heater
Consult your Flinn Scientific Catalog/Reference Manual for current prices.
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© 2016 Flinn Scientific, Inc. All Rights Reserved.