Chemical equilibrium demonstrations show how reactions can reach a balance between forward and reverse processes. They are valuable because equilibrium is an abstract idea that becomes much clearer when seen in action.
| Demonstration | Materials | Difficulty | Safety | Summary |
|---|---|---|---|---|
| Blue Bottle Experiment | ★★☆ | ★★☆ | ★★☆ | In the Blue Bottle Experiment, a solution of glucose, potassium hydroxide, and methylene blue alternates between colorless and blue when shaken. |
| Cobalt Chloride Equilibrium | ★★☆ | ★★☆ | ★★☆ | A solution of cobalt(II) chloride in ethanol appears blue due to formation of [CoCl4]2–. When water is added, the equilibrium shifts toward the hydrated [Co(H2O)6]2+ complex, producing a pink solution. |
| Equilibrium of Iron (III) Thiocyanate | ★★★ | ★★☆ | ★★★ | The equilibrium between iron(III) ions, thiocyanate ions, and the red-brown ferric thiocyanate complex can be shifted by adding or removing reactants. Color changes from yellow to red-brown or vice versa demonstrate Le Chatelier’s principle in action. |
| Nitrogen Dioxide and Dinitrogen Tetroxide Equilibrium | ★★★ | ★★★ | ★★★ | The equilibrium between brown nitrogen dioxide gas (NO2) and colorless dinitrogen tetroxide gas (N2O4) can be studied in a closed syringe system. Changes in pressure, volume, and temperature shift the equilibrium, which can be observed as changes in the intensity of the brown color. |
Materials
★☆☆ Easy to get from supermarket or hardware store
★★☆ Available in most school laboratories or specialist stores
★★★ Requires materials not commonly found in school laboratories
Difficulty
★☆☆ Can be easily done by most teenagers
★★☆ Available in most school laboratories or specialist stores
★★★ Requires a more experienced teacher
Safety
★☆☆ Minimal safety procedures required
★★☆ Some safety precautions required to perform safely
★★★ Only to be attempted with adequate safety procedures and trained staff