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This week's LabZone activity
Dec. 14, 2005
Rusting Wool
Start a chemical reaction and find out more about chemical reactions, oxygen, oxidation, and the composition of air.
Description:
Steel wool combines with oxygen in controlled conditions.
You Will Need:
- shallow dish
- toothpicks or wood splints
- tall, slender glass jar
- steel wool, size 0000, soap free
- wax marker
- drinking straw or rubber tube
Instructions:
Do not use steel wool pads that contain soap or cleaners. Use 0000 steel wool, It is sold in hardware and paint stores. Partially spread apart the fibers of the pad. Moisten a pad with tap water and shake off excess water.
Shove the pad to the bottom of the glass jar. Do not compress the fibers of the steel wool pad. Invert the jar. The pad should remain lodged near the bottom (now the top) of the jar.
Fill the shallow dish with water. Place several toothpicks, wood splints, bottle caps, or other items in the bottom of the dish to create lifting blocks for the jar. Place the inverted mouth of the jar on the blocks in the water.
Initially, the water level in the jar must align with the water level in the dish. Use a straw or rubber tube to remove or add air to the interior of the inverted jar. Remove the tube or straw once the water levels are equalized. Use a wax marker to indicate the initial water level, marking a line on the exterior of the glass jar.
Content:
Most of the oxygen in our atmosphere is in the form of a diatomic molecule: two atoms of oxygen bound together forming a molecule of O2. Some of the oxygen in our upper atmosphere is triatomic: three atoms of oxygen bound together to form a molecule of O3. The triatomic form of oxygen is commonly called ozone.
Oxygen is a product of photosynthesis. During that process, plants absorb carbon dioxide from the atmosphere and release oxygen.
Oxygen readily combines with many materials, including iron. The steel in the jar combines with oxygen to form iron oxide, or rust, which is the oxidation reaction that is taking place. The water level rises in the jar because oxygen is consumed in the reaction with the iron in steel wool. Oxygen remains in the jar, but not as a gas. Ambient air pressure outside the jar pushes water up into the jar as the oxygen is consumed. The volume of gas in the jar should decrease by 20%, corresponding to the portion of oxygen in the atmosphere.
Common fire is a reaction very similar to the rust reaction. It is a much faster reaction. A product of the combustion reaction is heat. Heat is released very slowly during the rusting process.
Teacher's Notes
Activity excerpted by permission of the Chemical Educational Foundation (www.chemed.org) from You Be The Chemist. For additional information about these activities and lesson plans, see www.chemed.org/Kit.html.
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