Page 15 - 新思维科学学生用书8 样章

1 Respiration

Think like a scientist

Comparing the carbon dioxide content of inspired air and expired air

In this activity, you will use limewater to compare how much carbon dioxide there
is in the air that you breathe in, with how much carbon dioxide there is in the air that
you breathe out.

Work with a partner to do this activity.

You will need:
• rubber tubing • glass tubing, as shown in the diagram

• two rubber bungs to fit the test tubes • two test tubes • limewater

Safety
It is very important that the rubber tubing is rubber tubing
perfectly clean before you use it. Do not share glass tubing
the mouthpiece with anyone else or put it on rubber bung

the work surface when you have finished.
Method test tube

1 Read through the method and make an
assessment of all the risks. Decide how limewater
you will overcome or reduce these risks.
2 Look carefully at the apparatus.
Starting with the rubber tubing, follow the A B

glass tube as it branches into the two test tubes.
What is different about the glass tubing that goes into test tube A and test tube B?
3 Now think about what might happen if you gently blow down the rubber tube.

Predict the tube in which you think bubbles will appear. Why do you think that?
4 Gently blow into the rubber tubing, until bubbles appear in one of the tubes.
Was your prediction correct?
5 Now think about what might happen if you gently suck the rubber tube. Try it.
Was your prediction correct?

6 Put your mouth over the end of the rubber tubing, and gently breathe in and
out. Bubbles will appear in one tube as you breathe out, and in the other tube
as you breathe in. Your partner will check the bubbles and can tell you if you are

doing it correctly.
Be careful – don’t suck too hard! Limewater is not poisonous, but it is not a
good idea to get it into your mouth.

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