In this activity, learners explore two properties of gases – that they 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.