BACKGROUND:
Air consists of gases
in different proportions depending on how high you are in the atmosphere.
It was a very difficult process to determine what air is composed of.
Joseph Priestly in the 1770's showed that air contained something that
living organisms needed to survive. He called it “phlogistons.”
In the 1780's French chemist Antoine Lavoisier determined that air contained
a gas, which he called oxygen. He also found out that air contained
two other gases - nitrogen and carbon dioxide.
Later, air was chemically found
to be about 21% oxygen, 78% nitrogen, and 1% carbon dioxide and other gases.
However, it wasn’t until the 19th century that researchers discovered that
the atmosphere changed with height. James Glaisher and Robert Cowell
risked their lives in balloons to find out about the atmosphere.
By 1902, unmanned balloons charted and defined the extent of the troposphere.
PROCEDURE:
- This exercise shows two different areas in
the atmosphere and the students must decide where they belong. You
may want to give them a clue, that one of the elements is essential to
humans, so it must be closer to the earth.
- Also ask them, if they were traveling in an airplane would
there be more oxygen up there or down on the ground. Would they be
able to breathe outside the airplane? You may have to discuss with
students that there is oxygen in the airplane that is brought from the
ground. If they are climbing a tall mountain, would they have trouble
breathing? Yes, because the air has different proportions of the
different gases, and oxygen becomes depleted.
- Give students the worksheet. Go through the activities
on the worksheet with students.
ANSWERS:
Nitrogen = N;
Oxygen = O;
Argon = Ar;
Carbon Dioxide = CO2;
Hydrogen = H;
Helium = He.
What composition of air do you think is found below 72 km? A
What composition of air do you think is found above 800 km? B
Why? B has lighter gases; organisms need oxygen so it should
be on the bottom.
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