Congratulations to Grazyna Zreda who solved the Chemical Mystery of the Mentos candies! To conduct this trick, two white Mentos candies are placed in separate beakers that both contain universal indicator. One of the Mentos candies turns the indicator slightly green, indicating the presence of base. The other Mentos candy turns the indicator red, indicating the presence of acid. The trick is that one of the candies is a regular mint Mentos (which contains no citric acid), while the other is a fruit Mentos (which does contain citric acid). The outer, colored layer of the fruit Mentos is removed prior to the experiment. When this is done, the fruit Mentos looks very much like a regular white mint Mentos.
Citric acid is added to fruit Mentos to give it a slightly sour taste. Many other types of fruit candies contain acids, too. Of course no one wants their mints to taste sour, so no acid is added to mint Mentos. One thing I’m curious about with this experiment is why the mint Mentos tends to change the indicator to a slightly basic color. I don’t see anything in the ingredients of the mint Mentos that would indicate a base. Maybe someone could tell me what I might be missing…?
To see how you can pull of this trick, see the video below.