Colour Changes Demonstrations

Colour (or color - we haven’t decided yet!) shifts are clear signs of physical or chemical change. They give visible evidence of processes at the particle level and help connect what we see to the underlying science.

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.
Chemical Sunset	★★☆	★★☆	★★☆	When sodium thiosulfate reacts with hydrochloric acid, colloidal sulfur particles form. As the particles grow, they scatter shorter wavelengths of visible light and transmit longer wavelengths, producing a sunset-like sequence of colors when projected with an overhead projector.
Chemical Traffic Light	★★★	★★☆	★★☆	The Chemical Traffic Light experiment demonstrates reversible redox reactions using glucose, sodium hydroxide, and indigo carmine. The solution transitions through a sequence of colors (blue → green → red → yellow) and can be reset by shaking, as oxygen from the air re-oxidizes the indicator.
Color Changing Walking Water	★☆☆	★☆☆	★☆☆	Cups filled with colored water are connected by folded paper towels. The water climbs up the paper towels and travels into empty cups through capillary action. As the colors mix in the empty cups, a rainbow effect is created.
Color Changing Water	★☆☆	★☆☆	★☆☆	A glass of blue-colored water is placed inside a bowl, and the bowl is then filled with yellow-colored water. When looking through the bowl, the overlapping yellow and blue liquids appear green, even though the water in each container stays its original color.
[New Demonstration]	★★★	★★☆	★★☆	A disappearing ink solution is created using the acid-base indicator thymolphthalein. It appears dark blue when basic, but fades to colorless as carbon dioxide from the air lowers the pH. The fading can be sped up with vinegar or slowed down with additional base.
Dry Ice pH Colour Change	★★★	★★☆	★★☆	Adding dry ice to a beaker of water with universal indicator creates bubbling fog and a color change. As carbon dioxide dissolves into the water, the solution becomes acidic and shifts from green through the color spectrum to orange. Adding base resets the cycle.
Dry ice Rainbow Colors	★★★	★★☆	★★★	When dry ice is added to indicator solutions, the solid carbon dioxide sublimates, producing bubbles and fog that look like boiling. As carbon dioxide dissolves in water, it forms carbonic acid, lowering the pH and causing the indicator solutions to change color dramatically from their basic to acidic forms.
Iodine Clock	★★☆	★★☆	★★☆	Two clear solutions are mixed, and after a short delay the mixture suddenly turns deep blue. The timing of the color change depends on concentration and temperature, making this a classic demonstration of chemical kinetics.
Lead Iodide Precipitation	★★☆	★☆☆	★★☆	When aqueous lead(II) nitrate reacts with aqueous potassium iodide, a double displacement reaction occurs. Potassium nitrate remains dissolved, while lead(II) iodide precipitates as a bright yellow solid.
Lemon Juice Invisible Ink	★☆☆	★☆☆	★★☆	Lemon juice is used to write a hidden message that becomes visible when heated with an iron.
Milk of Magnesia Changing Colors	★★☆	★★☆	★★☆	Milk of magnesia, a suspension of magnesium hydroxide, is mixed with a universal indicator to show its alkaline nature. When vinegar is added, the solution rapidly shifts through the color spectrum as the acid reacts with the base, demonstrating how antacids neutralize stomach acid.
Oscillating Clock Reaction	★★★	★★☆	★★☆	The Briggs-Rauscher reaction is a dramatic oscillating chemical reaction in which a solution alternates between amber and blue-black colors several times before settling into a final dark-blue state. The color changes are caused by the interplay of iodine species, hydrogen peroxide, malonic acid, starch, and a manganese catalyst.
Solid Lead Nitrate and Potassium Iodide	★★☆	★☆☆	★★☆	When lead nitrate and potassium iodide powders are combined and shaken, they undergo a double displacement reaction to produce yellow lead iodide.
Vanadium Oxidation States	★★★	★★☆	★★☆	This experiment demonstrates the multiple oxidation states of vanadium by producing vivid colors (yellow, green, blue, dark-green, and purple) in a single solution. Starting from vanadium pentoxide, vanadium compounds are reduced with zinc and then re-oxidized with potassium permanganate, creating a reversible rainbow of colors.
Water to Wine to Milk to Beer	★★☆	★★☆	★★★	This dramatic chemistry demonstration makes a liquid appear to transform into water, wine, milk, and beer as it is poured from one glass to another. The sequence involves pH indicators, precipitate formation, and gas release, illustrating multiple chemical concepts in a visually striking way.

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