Today in my organic chemistry class, after all of the glassware had been cleaned and people started to trickle out, we got to playing with some universal indicator and made this.
It’s not food coloring- the same pigment is used in each of these, Fisher’s Universal Indicator is a combination of pigments which change color depending on the pH of the solution. From left to right, the solutions go from quite acidic to very basic. At a neutral pH as in pure water, Fisher’s Indicator is green.
It was a lot more work than you might expect- the reagent expired in 1993 (thank you, public education!) and many tears were shed- mostly mine. We used varying combinations of HCl, NaOH, distilled water, and our slightly acidic tap water.
The purple is kind of lame. We tried to get a better purple by shoveling solid pure lye* into the mix but no avail. You can only do so much when your reagent has been expired for almost two decades.
*Remember kids, do NOT try this at home.