Monday, October 17, 2016

13 Days of Halloween: Color Changing Liquid

Here is a great Chemistry trick to get your students guessing.

4 or more tall clear containers
Red Cabbage Juice Extract (See directions below)
Baking Soda
Epson Salt or other salts
Lemon Juice
Rubbing Alcohol

Other substances to try:  vinegar, baking powder, apple juice, nail polish remover.  Always make sure the liquids or powders you choose can be mixed with water.  I try to use common kitchen items.

Please wear safety goggles.

How to Make Red Cabbage Juice Extract

Red cabbage juice is an acid/base indicator.  This means it will change color in the presence of an acid or a base.  It will turn red/pink in the presence of an acid and green in a base.  There are many colors in between.  The more acidic the more pink.  The more basic the more green.

Purchase a red cabbage at the store.  They are about $0.99 a pound.  I paid $1.50 for a small one.  Take off a bunch of the leaves and place them in a pot.  Cover the pot with liquid.  Bring water to a boil and boil about 15 minutes or so.   You want to boil it until the color is pretty much out of the leaves.  The liquid should be a nice purple color.  Allow to cool and then pour the liquid into a container.  One cabbage will make more than you need.  I will make a batch and freeze some for
future use.

 Set-up for the Students. 

Make sure they don't see you do this part.

Place the tall containers on a table in front of where your class will sit.  Fill each with about 200ml of liquid.  You want to make sure there is enough room left for adding red cabbage juice.
Place the following in each container:
Container 1:  plain water
Container 2:  Add a teaspoon of baking soda and stir until dissolved
Container 3:  Add a teaspoon of Epson salt or another salt.  Stir until dissolved.
Container 4:  Add a teaspoon of lemon juice.  Stir.
Container 5:  Add a teaspoon of rubbing alcohol.  Stir
Other ideas could be vinegar which is a strong acid or baking powder which is a base.  Anything that will dissolve clear so that it looks like water should be in all of the containers.

Demonstrating for the Students

Make sure they can see the containers.  Tell them you are going to pour in a special liquid into the tall containers.  Don't tell them anything else.  Quietly pour them into each container until they change colors or are pretty full.  Ask the students what happened and why.  They are sure to be surprised. 

Here are some great links on acids and bases to help with explanations.

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