A few weeks ago, we looked at a classic experiment of putting a lit
candle under a glass. We saw that water was drawn into the glass, not
by the oxygen being burned up, but by the cooling of the air in the
glass after the candle went out. This week's experiment will allow us
to do what many people thought the first experiment was doing.
You will need:
a pie pan
water
a clear glass or jar
steel wool
vinegar
tape
Carefully fit a wad of steel wool into the bottom of the glass. If it
does not fit tightly, then use some tape to hold it in place. Pour a
little vinegar into the glass, to wet the steel wool. Pour off any
excess vinegar. Pour about two inches of water into the pan. Place the
glass upside down in the pan of water. The jar will be full of air,
with the steel wool at the top.
Let the jar sit in the pan over night. You may want to look at it
periodically to see what happens to the water level, but do not move it
until the next day.
What happened? You should find that the water has risen into the glass.
You should also find that the steel wool has rusted. The two things are
connected. When iron or steel rust, they combine with oxygen to form
iron oxide (rust). As the steel wool rusted, it took the oxygen out of
the air. This lowered the air pressure in the glass, allowing the
outside air pressure to push water into the glass to balance the
pressure. When the rusting steel wool has removed all of the oxygen
from the air in the glass, the water should have risen 1/5 of the way
up the glass, as oxygen makes up about 1/5 of the air around us. Almost
all of the rest of the air is made up of a gas called nitrogen.
When iron rusts, it gets heavier, as the iron is bonding with the
oxygen in the air. When iron filings are burned, they also get heavier,
for the same reason. This was one of the first proofs of the existence
of the gas oxygen.
Back
to Krampf Index Including permission to post
these
experiments on my web site.
