Sunday Science: Colorful Changes

We did a fun experiment today using Bromothymol Blue (BTB), which is a chemical that changes color when exposed to acids or bases.  I purchased it on from a chemical supplier pretty inexpensively, and you only need to use a little – just put a small amount in a cup and add water.

To set up the experiment, I set out several clear plastic cups and got out our various supplies.  I filled the cups half full with the BTB / water mixture and then let the kids take turns adding things to see what would happen.  The older kids created a table to document the results.

Here are the things we added to it and the results:

Baking soda:  stayed blue

Effervescent tablet (we used generic denture cleaner):  bubbles turned yellow, then once they were gone it was blue

Vinegar:  turned yellow

Vinegar and baking soda:  lots of bubbles, in fact bubbled over – use a tray!  And, it turned yellow and felt cold.

You can also add Calcium Chloride (CaCl2) – sold as ice melt, but you need straight CaCl2 and we could only find a blend!  It won’t change the color but will make the cup feel cold.  If you combine CaCl2 and baking soda you’ll get milky yellow bubbles.

Post a comment if you find anything else fun to add!

What Do You Think?