Objective
To create a “gas fountain” using glassware and a simple chemical reaction, demonstrating the relationship between gas solubility and pressure. This experiment combines visual appeal with fundamental chemistry concepts.
Materials
- Round-bottom flask (500mL)
- Long glass tube (1cm diameter)
- Rubber stopper (single-hole, fits flask and tube)
- Funnel
- Large container (e.g., beaker or basin)
- Water dye (e.g., ink or food coloring)
- Sodium hydroxide solution (10%)
- Carbon dioxide gas generator (marble and dilute hydrochloric acid)
Procedure
Prepare the Fountain Apparatus:
- Add about 1/4 volume of water to the round-bottom flask and tint it with dye for visibility (e.g., blue or red).
- Seal the flask with the rubber stopper, inserting the long glass tube through the stopper. Ensure the top of the tube extends slightly above the stopper.
Generate Carbon Dioxide:
- In the gas generator, combine marble (CaCO₃) with dilute hydrochloric acid to produce carbon dioxide gas.
- Slowly introduce the CO₂ gas into the flask, replacing the air inside, until no bubbles escape from the flask.
Initiate the Fountain:
- Submerge the lower end of the glass tube into a large container filled with sodium hydroxide solution.
- Quickly pour a small amount of water (about 5mL) into the top of the glass tube using a funnel.
Observe the Phenomenon:
- Instantly, the colored water in the flask will be rapidly drawn up through the glass tube, creating a spectacular fountain effect.
Scientific Explanation
Carbon Dioxide Solubility and Pressure Changes:
- When water is added to the tube, CO₂ gas in the flask dissolves into the water. The reaction is accelerated when the gas reacts with sodium hydroxide to form carbonate, further reducing gas pressure inside the flask: CO2+2NaOH→Na2CO3+H2OCO_2 + 2NaOH → Na_2CO_3 + H_2OCO2+2NaOH→Na2CO3+H2O
- The pressure drop inside the flask, compared to atmospheric pressure, causes the external liquid to be “sucked” into the flask through the glass tube.
Sustained Fountain Effect:
- As CO₂ continues to dissolve and react, the pressure difference remains for a few seconds to over ten seconds, sustaining the fountain effect.
Safety Notes
- Wear gloves and goggles when handling dilute hydrochloric acid or sodium hydroxide to prevent skin or eye irritation.
- Perform the experiment in a well-ventilated area to avoid CO₂ buildup.
- Inspect glassware for cracks or damage to prevent accidents under pressure.
Fun Factor
This Gas Fountain experiment merges chemistry and physics, using glassware to showcase the fascinating interplay of gas solubility, pressure, and chemical reactions. The colorful fountain effect is highly engaging and ideal for science classes or outreach demonstrations!