Hot and Cold Pink Color Change Chemistry Demonstration


Valentine’s Day Color Change Chem Demo

Watch a solution change from pink to clear and back again with the hot and cold demonstration. (Ty Nigh)

Watch a solution change from pink to clear and back again with the hot and cold demonstration. (Ty Nigh)

This is a fun color change chemistry demonstration, just right for Valentine’s Day. Take a pink solution and watch it turn colorless upon heating. When the solution cools it becomes pink again. Here’s what you do:

Prepare the Hot and Cold Valentine Solution

Add a few drops of phenolphthalein indicator and a drop of concentrated ammonia to 500 ml of water in a beaker, flask or large test tube.

Perform the Valentine’s Day Demo

Present the pink solution. You can heat the liquid over a hot plate or, in the case of the test tube, in a burner flame. Heating the solution causes a shift in the equilibrium between the unionized ammonia and the ionized ammonium hydroxide. The change in pH makes the pink-colored indicator turn colorless. If you do not experience a color change, there is too much ammonia in the solution, so dilute it further with water and try again.

More Valentine’s Day Science Experiments

The hot and cold demonstration is one of several Valentine’s Day science experiments to try:

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