Citric Acid Volcano
Difficulty: Very Easy | Time: 5 minutes | Visual Impact: High
Historical Context
The reaction between acids and carbonates has been known for centuries. Joseph Black’s 1756 discovery that carbonates release “fixed air” (carbon dioxide) when treated with acid was a landmark in chemistry, helping to overturn phlogiston theory.
The volcano demonstration became a staple of science education in the mid-20th century, popularized by science fairs and educational television. While usually done with vinegar, citric acid provides a more reliable and controllable reaction. The combination of acid-base chemistry with the visual drama of an “eruption” has introduced millions of children to chemistry.
Materials
- Baking soda - 30g (2 tablespoons)
- Citric acid - 15g (1 tablespoon)
- Warm water - 100mL
- Food coloring - 3-4 drops (optional)
- Dish soap - 1 teaspoon (5mL)
- Beaker or flask (250mL+)
Procedure
- Place 30g baking soda in container
- Add dish soap and food coloring
- Dissolve 15g citric acid in 100mL warm water
- Pour citric acid solution onto baking soda
- Watch vigorous CO₂ production create foam volcano!
Reaction
\[\ce{C6H8O7 + 3 NaHCO3 -> Na3C6H5O7 + 3 H2O + 3 CO2}\]
The Science
Classic acid-base reaction producing carbon dioxide gas. The soap traps bubbles creating dramatic foam. Citric acid is triprotic (can donate three hydrogen ions), so it reacts with three molecules of baking soda.