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Finding CO2 Mass in your Breath (16 Favorites)

LAB in Concentration, Precipitate, Net Ionic Equation, Balancing Equations, Stoichiometry, Limiting Reactant, Mole Concept, Dimensional Analysis. Last updated March 26, 2020.


In this lab, students will measure how much carbon dioxide they exhale by reacting their exhaled breath with lime water (calcium hydroxide).

Grade Level

High school


By the end of this lesson, students should be able to

  • Carry out calculations involving reactants.
  • Better understand the concept of limiting reagents.

Chemistry Topics

This lesson supports students’ understanding of

  • Net ionic equations
  • Stoichiometry
  • Limiting reactant
  • Concentration


Teacher Preparation: 20 minutes

Lesson: 2 class periods


  • goggles
  • straw
  • 250 mL beaker (2)
  • saturated Ca(OH)2 solution
  • filter paper
  • timer
  • funnel
  • balance


  • Always wear safety goggles in the lab when carrying out an investigation.
  • Remind students to exhale through the straw, do not inhale the limewater.
  • Students should wash their hands thoroughly before leaving the lab.
  • When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.

Teacher Notes

  • This lesson assumes students are familiar with solving mass-mass stoichiometry problems and the concept of limiting reactant. They don’t need to solve for limiting reactant but be familiar with the concept.
  • The lesson will take at least two periods separated by one day to complete. The use of the drying oven on a “low” setting will require a longer time to dry the precipitate, but a higher setting runs the risk of scorching the paper.
  • This lesson can be modified for a more “inquiry” method, where students are required to create their own procedure and justify what kinds of data they are collecting.
  • The Student Activity Sheet is designed so it can be cut in half; this economizes resource use use which is always a good thing to model for your students in chemistry.
  • Waste solutions are neutralized with vinegar and dumped down the drain. This can also be accomplished by the students; adding some phenolphthalein indicator can add a “splash” to this otherwise mundane chore of environmentally responsible waste disposal. Please review all safety precautions prior to any lab.
  • For ESL students, portions of this lab can be modeled ahead of time; for example, the procedure of filtration, rinsing, and drying can be demonstrated via a teacher presentation prior to this lab. Small heterogeneous lab groups likewise can help students who may be struggling with the language in the lab understand what is expected of them. In terms of understanding the calculations, all students can benefit from prior instruction including direct instruction, small group practice, and student-led problem solving sets.

For the Student



Wear goggles and apron at all times.


  1. Obtain about 100 mL of saturated Ca(OH)2 (lime water)
  2. Using a straw, take a big breath and exhale (not inhale!) into the lime water. Time how many seconds you are blowing. Record the time.
  3. Write your name on a piece of filter paper and find its mass. Record the mass.
  4. Filter the white precipitate and place on watch glass in drying oven. Use funnel and filter paper from #3.
  5. After it is dry, find the mass of your filter paper. Subtract the mass of the filter paper and record the mass of the CaCO3 that you collected.


  1. Write the balanced net-ionic equation for the reaction of carbon dioxide and calcium hydroxide.
  2. Identify the limiting reagent in your equation from #1. Justify your answer.
  3. Calculate the number of moles of calcium carbonate that were collected in the filter paper.
  4. Calculate the number of moles of carbon dioxide that reacted to form the calcium carbonate.
  5. Calculate the number of grams per second of carbon dioxide that you exhale. Compare your value to others in the class. Create a hypothesis of why there are differences/similarities.
  6. Predict how the results of your experiment might change if: (Justify your predictions)
    a. you were doing exercise before exhaling into the lime water
    b. you were sick and running a fever of 100 °F
    c. the temperature of the lime water was warmed to 55 °C.
    If time permits, repeat the experiment testing one of them.