I’ve been wanting to do this simple kitchen science experiment with my kids for awhile now as I used to do this with my middle school students once upon a long time ago…This one is fantastic for superheroes of ALL ages. The younger ones can enjoy the colorful reactions and the older ones can learn a bit about acids and bases and how pH indicators work.
Here’s what you need to get started:
- Red Cabbage (Why is it called red when it really looks purple??)
- Large Pot
- Ice Cube Tray (or several small clear cups/jars)
- Droppers (I save the ones we get from the pharmacist everytime one of my superheroes needs meds)
- Coffee Filters (optional)
- Household liquids to test (water, vinegar, lemon juice, fruit juice, milk, baking soda/water, soda, laundry detergent, liquid soap, ammonia, etc…)
To make the Purple Potion:
Coarsely chop up half a head of cabbage.
Place it into a large pot and add water. I added about 5 cups of water to mine.
Bring the cabbage/water mixture to a boil and then let simmer for about 15-20 minutes. Make sure you have your exhaust fan on and your windows open. This gets stinky 🙂
Remove from heat and let cool to room temperature so that it doesn’t burn your little ones. Once cool, strain the mixture so that only the purple liquid is left. Discard the cabbage.
I ended up with about 4 cups of Purple Potion. Now we are ready to experiment!
I placed an ice cube tray in front of each of the Superheroes. I placed a variety of liquids from the kitchen into several wells of the tray. We used: water, milk, lemon juice, liquid soap, baking soda (dissolved in water), vinegar, apple juice, liquid soap and laundry detergent.
I had them color in what the liquids looked like before we started.
This is the observation sheet they used:
Each superhero got a small cup of Purple Potion in a cup and a dropper.
They added several drops of the purple potion to each well and observed the changes.
Whoa! Look at all those colors! Why is it doing that?
Here are the final results:
I asked them what might happen if they start mixing some of the liquids together. A whole new set of experiments to do!
My older son made a pink concoction and said it looked like “antibiotics”! (Can you tell how sick we’ve been this past winter! )
With my older son, I probed him on what the pink colored liquids had in common and what the blue colored liquids had in common. I think this was a bit over the top for a 6 yr old and he really was a bit lost at what to say. If you have older kids, definitely ask. The goal is to see if they can come up with some common characteristics of acids and bases. (Even my middle school students used to struggle with this)
I decided to try to make my own indicator paper with some of the Purple Potion. I placed 4 coffee filters in a container and added some Purple Potion to it.
I soaked the filters overnight. Make sure to use an airtight container with a lid or your kitchen will stink in the morning!
Remove the paper from the liquid and let dry completely. I left mine outside to dry in the sun.
Cut into strips and you’re all set!
Instead of using droppers to test the liquids, you can dip the indicator paper into the liquids and see the paper change colors.
And then they placed it on their observation sheet to compare with their previous results
Science Behind the Activity:
Cabbage juice acts as a pH indicator. Without getting too deep into the chemistry of it all, substances that are acidic (pH between 0-7) will turn varying shades of pink/red when mixed with cabbage juice, Substances that are basic (pH between 7-14) will turn varying shades of green-ish/blue when mixed with cabbage juice. There are several types of indicators that are used for different purposes. Litmus paper is specially treated paper that turns red in the presence of an acid and blue in the presence of a base. By treating the filter paper with cabbage juice, you can create a simple version of indicator paper. There are also several different types of indicator paper as well, many that can give you an approximate pH of the substance being tested so that you can tell just how acidic or how basic the substance is.