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Oxygen in air
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      Two magnets.
      Glass flask.
      Glass bottle.

      Iron powder.
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     1. Fill half of the bottle with water.

     2. Cover the magnet surfaces with iron powder.

     3. Place the magnet with the iron powder inside the glass bottle.

     4. Outside the bottle, with the help of another magnet, hold the magnet with iron in the top off the bottle. (the magnets shouldn't be in contact with water)

     5. Turn the glass bottle upside down inside the glass flask, submerging part of it.(now we have a closed system inside the bottle)

     6. Mark the initial water level in the inverted bottle.

     7. Verify how the water level is changing periodically during the next 24 hours. What happens?

In this experiment you can observe that the water level inside the bottle arises about 20% of the air total height. Inside the inverted bottle we have air, a magnet and iron powder. The air is constituted by nitrogen (79%), oxygen (20%) and other gases (1%). The iron oxidizes (formation of iron oxide) in the presence of an atmosphere that contains oxygen. In the present experiment, the iron powder in the magnet reacts with the oxygen arising the water level. That happens because the product of the reaction between the iron and the oxygen is solid. As we know, a solid occupies less volume comparatively with a gas. At a certain moment, the level of the water stays unaffected because the iron oxidation ceases due to oxygen lack. Try it at home!

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