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Activity #8
A Cure for "Bad" Breath ?

Grade Level: K-4

Module: Cardiovascular

Overview

Animals generate carbon dioxide as part of their respiration process. If too much carbon dioxide builds up in an enclosed environment, animals can suffocate. Plants naturally replenish the oxygen (O2) and scrub (remove) the carbon dioxide from the air. This is part of the natural process of interdependence in the environment. With small animals a sustainable system of plants and animals can be achieved fairly easily. A problem arises with larger warm blooded animals that have higher metabolic rates and produce much larger quantities of CO2. Just a few plants cannot scrub enough carbon dioxide from the air to keep humans from suffocating. In this case we use chemical means to scrub the air.

Key Question

  • How can "pure" air be maintained in space?
  • How can air be cleaned so that excess carbon dioxide is removed?

Time Frame:

1 class period

Materials

  • Medium-sized flasks or bottles fitted with two-hole stoppers or clay to seal the tops of the flasks (see Figure)
  • Tubing or flexible straws
  • Carbon dioxide source (e.g., chalk in acid or baking soda in vinegar) OR have a students breathe into the flasks
  • Calcium hydroxide
  • Lime water

Getting Ready

Before beginning the activity, be sure that you have assembled all of the necessary materials. Chemicals can be obtained from chemical supply stores or science companies.

Classroom Activity

  1. Ask your students, "What would be the best way to maintain breathable air in a space ship?" Tell your students about the importance of keeping too much carbon dioxide from building up in an enclosed environment. Bring out some of the points that are expressed in the Overview-that animals generate carbon dioxide as part of their respiration process, and that if too much carbon dioxide builds up in an enclosed environment, animals can suffocate. Plants replenish oxygen (O2) and scrub (remove) the carbon dioxide from the air. However just a few plants on a space ship cannot scrub enough carbon dioxide from the air to keep humans from suffocating. In this case we use chemical means to scrub the air. Tell the students they will be doing experiments in scrubbing carbon dioxide from air.

  2. Explain that lime water is an indicator of carbon dioxide gas. Air that people exhale or breathe out contains carbon dioxide gas. In the presence of lime water, carbon dioxide produces a fine powdery precipitate that makes the solution appear milky white.

  3. Have the students set up the apparatus as shown in the diagram below. Place lime water in each of the four beakers. Set up beakers #2 to #4 as "scrubbers." Add calcium hydroxide to each of those beakers. Calcium hydroxide reacts with carbon dioxide, binding it and removing it from the air.

  4. Students should observe the color of the liquid in each of the four beakers for 10 minutes. Have someone exhale into the straw or tubing continuously for the entire time.

    illustration of activity set up

Student Record Sheet

Record your observations on the table below:

student record sheet

  1. Was there a difference between the color of the liquid in the beakers?

  2. If so, why did this happen?

  3. Why is "scrubbing" air in spacecraft important?

  4. Why doesn't air need to be "scrubbed" on earth?

  5. Could you make a more efficient air scrubbing device? If so, how? <

Wrap-up Session

At the conclusion of the activity, allow the students to share their observations and conclusions with others in their class. Have a class discussion about the questions on the Student Record sheet.

More Activity Ideas

Challenge students to design an air scrubbing device that is more efficient.

Background for Teachers

Prerequisites:

  • Ability to record data

Vocabulary:

  • Scrub - to remove impurities; in this case to chemically remove impurities from a gas
  • Interdependence - a state of depending on one another
  • Carbon dioxide - compound with molecules consisting of one carbon atom bound to two oxygen atoms
  • Oxygen - element 16 in the periodic table; essential for respiration
  • Carbon - element 14 in the periodic table, essential for "carbon-based lifeforms" like ourselves

Skills:

  • Set up laboratory apparatus
  • Record data
  • Control variables in an activity

Concepts:

  • Air purification
  • Scrubbing
  • Recycling
  • Competition between chemical reactants (lime water and CaCO3 compete for available CO2)

Keywords: Scrubbing, Air Quality, Interdependence.

 
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