It's a Gas!

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In this activity, learners explore two properties of gases: gases take up space and exert pressure. Learners assemble two flasks and a beaker, connecting them with stoppers and tubing. They combine baking soda, water, and citric acid in a flask and then stopper the flasks. Gas (carbon dioxide) from the chemical reaction flows into a second flask, displacing colored water from the second flask into the beaker. An extension to this activity uses the gas created to put out a candle flame. This activity is currently used in the Nature of Matter Unit in OMSI's Chemistry Lab. Cost estimates are per 100 learners. For safety reasons, this activity is best suited as a demonstration for younger audiences.

Quick Guide

Preparation Time:
30 to 45 minutes

Learning Time:
Under 5 minutes

Estimated Materials Cost:
$5 - $10 per group of students

Age Range:
Ages 11 - adult

Resource Types:
Activity, Experiment/Lab Activity


Materials List (per group of students)

  • 500-mL Erlenmeyer flask with a tightly fitting rubber stopper with one hole
  • 250-mL Erlenmeyer flask with a tightly fitting rubber stopper with two holes
  • 400-mL beaker
  • 100-mL graduated cylinder
  • 250-mL squeeze bottle
  • 500-mL bottle
  • (3) pieces of glass tubing, 1.5 in long, to fit tightly thorugh the three holes in the rubber stoppers.
  • 3 ft plastic tubing same diameter as the glass tubing
  • 5 in plastic tubing to use as joints connecting the glass and the long plastic tubing
  • blue food coloring
  • (2) small jars with lids (about 200cc size)
  • (2) 1/2tsp measures
  • (2) 4lb boxes baking soda
  • 1 kg citric acid, crystalline
  • 100-mL beaker (optional)
  • votive candle (optional)
  • matches or lighter (optional)


  • Physical Sciences
    • Chemistry
      • Chemical Reactions
      • Acids and Bases
    • States of Matter
      • Gases


To use this activity, learners need to:

  • see
  • see color
  • read
  • touch

Learning styles supported:

  • Involves hands-on or lab activities


This resource is part of:

Access Rights:

  • Free access



Funding Source:

  • National Science Foundation, 9355628