Purple Brew: An Acid-Base Indicator

Next time kids say they don’t like vegetables, try out an experiment that will bring out the fun side of our leafy friends. Mom and Kiddo of  the blog What Did We Do All Day? shows us how to play with color in this demonstration that uses an acid, a base, and a vegetable. She suggests keeping some of the solution in the fridge for a rainy day and allowing kids to experiment on their own.

You will need:

• purple or red cabbage
• small and large glass jars
• baking soda
• water
• vinegar
• measuring cup
• 1/4 teaspoon

What to do?

1. Chop up a cabbage and simmer on the stove for 20 minutes to make a cool purple liquid (kids, please let a grown-up do this)
2. After the purple brew has cooled, collect some small and large jars. Place about 1/4 tsp baking soda and 1/4 tsp water in one jar, a small amount of vinegar in another and about 1/4 cup purple brew in a third.
3. Put some of the brew in a measuring cup and pour 1/4 tsp of the brew in each of the first small jars. What happens when you mix the purple brew with the different solutions?
4. In the jar filled with a 1/4 cup of purple brew,  pour about 1/4 cup vinegar. What happens?
5. Next, add 1/4 tsp baking soda to the same solution. What is your observation?

How does it work?

Red cabbage contains a chemical called flavin and flavin has the ability to change color based on the pH level of certain liquids. Nuetral solutions, (like water) are purple. Acid solutions, like the vinegar, turn will turn flavin red. Basic solutions, like the baking soda water, become blue.

You can check out Mom and Kiddo’s full post of this experiment HERE. Let us know what your results are when you make your own purple brew. What would happen if you tried different vegetables? What would happen if you used cream of tartar, lemon juice, salt, lemonade, or other materials from your kitchen pantry? Can you make your own litmus paper and test the pH of the solution?

Lemon Chemistry: An Acid-Base Experiment

Kari Wilcher runs a great blog. She was looking to teach her pre-school children about the Scientific Method while trying out some kitchen chemistry at the same time. Her plan was to show a dramatic acid-base reaction using lemons, baking soda, and a little dish soap. She writes:

“I firmly believe that children are never too young to be exposed to the scientific method and should follow it. I have found that the scientific method is very easy for them to understand, and follow, when presented to them in a simple way. I like to use a rebus (picture) to help my non-readers understand the directions. I also use these “big” words: data, hypothesis, prediction, and observation. We, including Momma, wear goggles (from the dollar store) and a lab coat (a.k.a. dad’s white button up shirt) because we are real scientists doing real science experiments…and it just makes us cool.”

You will need:

• Fresh Lemons
• A knife
• A small measuring cup & measuring spoon
• Baking Soda
• Liquid dish soap
• A clear cup for the reaction

What to do:

1. Roll the lemons on the counter like dough. This releases the juice inside the lemon.
2. Cut the lemon in half (adults only, please) and carefully squeeze out the juice into a small measuring cup. Note how much juice was created from each lemon and put the juice aside.
3. Into the empty glass place 1 Tablespoon of baking soda.
4. Add 1 teaspoon of liquid dish soap to the baking soda. Stir these up a bit.
5. Pour the lemon juice into the cup and stir. Now watch the lemon suds erupt!

How does it work?
This is a classic example of an acid-base reaction. This is often done with vinegar and baking soda, but we liked Kari’s “lemon twist.” The baking soda (a base) and the lemon juice (an acid) combine to release Carbon Dioxide gas. The liquid soap turns the bubbles into a foam that often erupts right out of the glass.

Try it out and let us know how it goes!

You can check out Kari’s full blog post of this experiment including the worksheets she created HERE.