Green to Red Color Change Christmas Chemistry Project

This green to red to green color change clock reaction is a perfect Christmas chemistry project. It’s a good example of a redox reaction and acid-base reaction, plus it’s a great opportunity to raise interest in chemistry.

Key Takeaways: Green to Red Color Change Christmas Chemistry Project

• This color change reaction shifts from green to red to green and back again.
• It demonstrates both redox and acid-base chemistry.
• The reaction is safe and suitable for classroom or home science demonstrations.
• Color changes occur due to the redox behavior of indigo carmine and pH shifts.
• Pouring from a height re-oxygenates the solution and resets the color.

Christmas Chemistry Demo Materials

The Christmas chemistry color change demonstration requires few materials, plus the chemicals are safe enough to rinse down the drain after use.

• Water (preferably distilled, but tap water is fine it the pH is nearly neutral)
• 15 grams glucose (C₆H₁₂O₆)
• 7.5 grams sodium hydroxide (NaOH)
• Indigo carmine indicator

The Christmas Chemistry Project

1. Prepare “solution A” by dissolving 15 g glucose in 750 ml water. Prepare “solution B” by dissolving 7.5 g sodium hydroxide in 250 ml water.
2. Warm solution A so it’s about body temperature (36-37°C or 98-100°F).
3. Add a pinch of indigo carmine to solution A. You just need enough to turn the solution visibly blue.
4. Pour solution B into solution A. This changes the color from blue to green. If left to sit, the color will change from green to red/amber.
5. Pour the red solution into an empty clear container from a height of at least 60 centimeters (2 feet). The height is needed to ensure enough oxygen dissolves in the solution to change its pH. The color of the liquid returns to green.
6. Once again, the color will change to red/amber. The demonstration may be repeated many times.

• Green = oxidized indicator at moderately basic pH
• Red/Amber = reduced indicator at high pH
• Color returns to green when oxygen from the air reoxidizes the dye

How It Works

Indigo carmine or indigotine is 5,5′-indigodisulfonic acid sodium salt with the chemical formula C₁₆H₈N₂Na₂O₈S₂. The dry salt is purple. Dissolved in water (usually as a 2% aqueous solution), it’s blue at pH 11.4 and yellow at pH 13.0. Indigo carmine is also used as a redox indicator that turns yellow when it is reduced. The glucose changes the color of the dye.

The reaction is much like that of the blue bottle demonstration, where the alkaline sugar solution reduces the dye to a paler or colorless leuco-dye. Shaking a flask or pouring the liquid from a height dissolves oxygen in the solution, oxidizing the dye back into its colored form. The rate of the color change depends on the concentration of the reactants and the temperature. Variations use potassium hydroxide (KOH) rather than sodium hydroxide (NaOH) and dextrose rather than glucose. Other pH indicators work to produce different colors.

Teaching Points

• Redox reactions: Glucose reduces the dye; oxygen reoxidizes it.
• Indicators: Indigo carmine shifts color with oxidation state and pH.
• Kinetics: The delay in color change demonstrates chemical reaction timing.
• Gas solubility: Pouring increases dissolved oxygen through aeration.
• pH effects: The dye color is pH-dependent.

Safety Information

As with all chemistry demonstrations, wear proper gear. Goggles, gloves, and a lab coat are recommended. At the end of the demonstration, the solution may be washed down the drain with running water.

Indigo carmine is safe enough for use as a food colorant (E132 or FD&C Blue #2). Aside from its use as a safe pH indicator, it’s also used as an intravenous dye for mapping the urinary tract, to color medications, to detect dissolved ozone, and to detect amniotic leaks. However, it can be irritating if inhaled.

Sodium hydroxide is a strong base. Eye or skin exposure causes irritation and chemical burns. Avoid contact with this solution and rinse any exposed areas immediately with water.

More Color Change Chemistry Fun

The “Christmas chemistry” demonstration is one of many color change reactions. Others to try include the blue bottle reaction (blue to colorless), vanishing valentine or hot and cold heart (pink to colorless), Halloween reaction (orange to black), water into wine (colorless to red), and Gatorade and drain cleaner reaction (blue to yellow).

Frequently Asked Questions (FAQs)

Q: Why does the solution turn red/amber after a few minutes?
A: Glucose reduces the dye over time, changing its oxidation state and color.

Q: Why does pouring from a height reverse the color?
A: Pouring dissolves oxygen in the solution, oxidizing the dye back to its colored form.

Q: Can I use other food dyes or indicators?
A: Yes, but results vary. Indigo carmine works best because of its redox sensitivity and pH range.

Q: Is the reaction reversible forever?
A: No, eventually the glucose is consumed and the solution becomes too diluted for a visible effect.

Q: Is this reaction safe to perform at home or in class?
A: Yes, with proper precautions. Use gloves and goggles. The final solution is safe to rinse down the drain with water.

References

• Cook, A. Gilbert; Tolliver, Randi M.; Williams, Janelle E. (1994). “The Blue Bottle Experiment Revisited: How Blue? How Sweet?”. J. Chem. Educ. 71 (2): 160. doi:10.1021/ed071p160
• Engerer, Steven C.; Cook, A. Gilbert (1999). “The Blue Bottle Reaction as a General Chemistry Experiment on Reaction Mechanisms”. J. Chem. Educ.. 76 (11): 1519–1520. doi:10.1021/ed076p1519
• Olah, Herbert W. Roesky (2007). Spectacular Chemical Experiments (1st ed.). Weinheim: Wiley-VCH. ISBN 978-3-527-31865-0.
• Pfennig, B. W.; Robert, R. T. (2006). “A Kinetics Demonstration Involving a Green-Red-Green Color Change Resulting from a Large-Amplitude pH Oscillation”. J. Chem. Educ. 83 (12): 1804. doi:10.1021/ed083p1804
• Summerlin, Lee R. (1988). Chemical Demonstrations (2nd ed.). Washington, DC: American Chem. Society. ISBN 9780841214811.