When some materials are exposed to the oxygen in the air a chemical reaction takes place. This reaction is called oxidation, and it forms the basis of a fun scientific investigation.
Take two thermometers, wrap the bulbs in steel wool, place them in separate dry jam jars and wait for five minutes. Take a measurement of the temperatures. Remove the steel wool from one of the thermometers and dip the wool into a dish of vinegar, making sure it's completely covered with vinegar. Squeeze it to remove excess vinegar.
Wrap the thermometer bulb in the steel wool again and put it back in the jam jar. Take the temperatures of the two thermometers every minute for 10 minutes. Record your results on a graph.
You should find that while the temperature of the first thermometer remains constant, it rises in the thermometer wrapped in steel wool soaked in vinegar. This is because of a chemical reaction - oxidation.
The vinegar has removed the non-reactive layer on the steel wool, exposing the iron in the steel to the air. The iron has reacted with the oxygen, and heat was released in the process.
A particularly common example of oxidation can be observed in cut apples.
Cut two slices from an apple. Lay each slice on a dish, and paint one with lemon juice.
Leave for 30 minutes. The uncoated apple will start going brown and lose some of its crispness. This is the result of oxidation. The apple coated in lemon juice will still be clear. The lemon juice has stopped the oxidation reaction.
To get students to work out what is stopping it, experiment further by trying a solution of vitamin C, salt, vinegar or baking soda.
Sophie Duncan is project manager for science at the BBC www.bbc.co.ukscience