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Unit 19: Biology Part 2 Page 102 of 137

What’s Happening: With enough blowing, the solution becomes green (or
even yellow if you really blow.) BTB is an indicator that becomes yellow
when the pH is lowered. The presence of carbon dioxide in your breathe
lowers the pH slightly, changing the color.

Experiment: How Much Air is in There?
Lung capacity is the amount of air in the lungs. When people have
respiratory diseases, their lung capacity is often decreased. What’s your
lung capacity? Let’s find out!

Materials:

 Milk jug
 Masking tape
 Water
 1 cup measuring cup
 Aquarium tubing

1. Place a strip of masking tape down the side of a milk jug from the
top to the bottom.

2. Fill the jug all the way up with water using a 1 cup measuring cup. Make
a mark on the tape after each cup you pour in.

3. Dump out about half the water, and record exactly how many cups of
water are left in the jug.

4. Place one end of a piece of aquarium tubing inside the mouth of the jug.

5. Take a normal breath and exhale through the tubing. Mark how high the
water goes.

6. Subtract the water amount after your breathe with the water height
before, to see how much air was in your breath.
7. Repeat steps 5 and 6, but breathe out as much air as you possibly can.

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