Praxis: Purple cabbage isn’t just for eating

By Medicine Hat News on March 3, 2018.

It was a great week being able to attend the South Eastern Alberta Teacher’s Convention and reconnect with colleagues and teachers I have not had the opportunity to chat with for quite some time. Thank you for taking the time to stop by and catch up and sign out some of the amazing resources we have here at Praxis. I know a big hit was our new Math Crate. Yes, math! Praxis is proud to offer STEM resources (science, technology, engineering and math) and we really felt that we needed to have some strong resources for our math educators as well. As a result of this need, a great math resource is now in circulation for all educators in our community! There are some exciting games, lessons, and hands on activities for your students to try out. I am excited to hear the feedback from teachers on how well it works in the classroom and how we can make it work for you in the classroom. If you are interested in signing out this new Crate, call Praxis and book it soon!

That said, I am still working on how to put a math activity in this column. It is not an easy task. Many of the resources we have involve templates, manipulatives and diagrams. I’ll keep working on that though. This week though, I am going to stick to my area of “expertise” — science. This activity comes up as a result of a teacher wanting some safe, simple classroom chemistry experiments for her class. I may be biased, but I often think chemistry is one of the most exciting areas of science with all of the colour changes and often “explosions” I do! This week, we are going to investigate acids and bases by making an indicator. Let’s get started!

*Remember to ask an adult before doing this experiment.

Materials

– one head of purple cabbage

– distilled water

– kettle

– knife

– cutting board

– spoon

– large glass bowl (heatproof)

– mesh strainer

– storage container/small dropper bottles

– plate

Procedure

1. Fill the kettle with water and plug it in to boil.

2. Please ask an adult to help you with this step. Using the cutting board and a sturdy surface, cut the head of cabbage into large slices.

3. Place the cut up cabbage into the bowl.

4. Pour the boiling water over the cabbage. Make sure it is entirely covered with water.

5. Set the mixture aside for at least 30 minutes.

6. Observe. What is happening?

7. Once the mixture is cool and the water is a nice deep purple colour, strain the cabbage out of the liquid.

8. Discard the cabbage.

9. You can put the indicator into small dropper bottles or in a large container and use a medicine dropper to dispense the liquid.

10. Test for the presence of acids and bases in some common household items. A suggested list is provided below:

What can I test?

* baking soda dissolved in distilled water

* lemon juice

* ammonia/window cleaner

* tap water

* milk

* pop

* fruit juices

* egg whites

* dish soap

* liquid hand soap

* anything else you can think of

11. Take a small amount of the liquid that you would like to test and place it on a plate.

12. Add a couple of drops of the cabbage indicator.

13. Observe what colour the solution turns.

What is going on?

You took a simple household substance and made an acid base indicator. You can purchase expensive acid base indicators from chemical supply companies, but that is not necessary. Purple cabbage juice is a great chemical indicator. An “indicator” is a substance that turns colour in the presence of acids and/or bases. For instance, when you added the vinegar (acetic acid) to the cabbage juice, it turned red. The darker the red colour indicates that it is a stronger acid. When you added the baking soda solution (sodium bicarbonate) which is a base, the indicator should have turned green. Pure or distilled water, which is neutral (neither an acid nor a base) will not have turned any colour, it should have stayed purple.

In our kitchen at home we can find many acids and bases. Lemons, limes, apple juice, coffee and of course vinegar are all acids. Baking soda and egg whites are basic.

Patty Rooks is senior scientific consultant at PRAXIS, “Connecting Science To The Community.” Contact Praxis at praxis@praxismh.ca, http://www.praxismh.ca, Tweet or follow us @PraxisMedHat, or friend us on Facebook.

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