In Chemical Mystery #18: Peek A Boo Blue,¹ Blue Powerade is observed to change to green, and then to a yellow color. When the yellow-colored solution is disturbed by pouring it, it shifts back to green or blue-green. Over time, this green-blue color fades back to yellow. The cycle of blue-colored Powerade fading to yellow, and then restoring a green or blue color by pouring can be repeated several times.

The experiment presented in Chemical Mystery #18 is a fascinating modification of the classic “blue-bottle” reaction.^2,3 One of the more interesting aspects of the modified reaction, which was first reported by my friend and colleague, Dean Campbell and his co-workers,⁴ is that the blue bottle reaction can be mimicked using grocery store items that contain Blue Dye #1 (BD1) like candy or Gatorade.

In the traditional blue bottle reaction, methylene blue in its oxidized, blue-colored form (MB⁺) reacts with glucose in the presence of base. This generates reduced methylene blue (MBH), which is colorless:^2,3,5

MB⁺ (blue colored) + glucose → MBH (colorless) + colorless products

If a solution containing MBH is disturbed in the presence of air, oxygen gas dissolves into the solution and oxidizes the MBH, regenerating the blue-colored MB⁺:

MBH (colorless) + O₂ → MB⁺ (blue) + HO₂^-

As demonstrated in Chemical Mystery #18, the ingredients in Powerade can be used to mimic the traditional blue bottle reaction. Blue Powerade is sweetened with glucose and colored with BD1. Indeed, BD1 can be reduced by glucose in the presence of base to form yellow-colored products:⁴

BD1_ox (blue colored) + glucose → BD1_red (colorless) + yellow products

Just like MBH, the colorless form of BD1 can be oxidized by O₂:

BD1_red (colorless) + O₂ → BD1_ox (blue)

Thus, simply adding base to Powerade sets up system that mimics the blue bottle reaction (Video 1).

As you can see in the video, the use of Powerade tends to cause a color that is more green than blue upon shaking. The green color likely results from a mixture of yellow products and the oxidized, blue-colored BD1. Also, sugar-free Powerade does not work in this experiment because it contains no available sugars that can reduce the BD1.

I have a few questions regarding this reaction that I’m still wondering about. First, what other drinks and grocery store items could be successfully used in this experiment? Can other color changes be generated when doing this experiment with products that contain dyes other than BD1? Some of these questions have been investigated by Campbell,⁴ but there are several more possibilities that can be tried out. Also, it is reported that the reduction of MB⁺ can only be achieved with reducing sugars (like glucose).^2-4 Based on this, it is likely that this experiment would not work with a drink containing BD1 but sweetened with sucrose (which is not a reducing sugar). Are there any drinks available that can be used to demonstrate this? Maybe you and your students can explore some of these questions. Be sure to let me know in the comments if you try to answer these questions and learn something new.

Happy experimenting!

References and notes:

1. Kuntzleman, T. https://www.chemedx.org/blog/chemical-mystery-18-peek-boo-blue (accessed August 2021).

2. Shakhashiri, B. Z. Chemical Demonstrations; University of Wisconsin Press: Madison, WI 1985; vol. 2, pp. 142-146.

3. Anderson, L.; Wittkopp, S. M.; Painter, C. J.; Liegel, J. J.; Schreiner, R.; Bell, J. A.; Shakhashiri, B. Z. J. Chem. Educ. 2012, 89, 1425-1431.

4. Staiger, F. A.; Peterson, J. P.; Campbell, D. J. J. Chem. Educ. 2015, 92, 1684-1686.

5. Reference 3 contains a very detailed description of the chemistry involved in this experiment.