Today my 5th graders learned how to use red and blue litmus paper, as well as use cabbage juice as an indicator. In the classroom, I had 6 solutions for them to test. They could test the solutions in any order they wanted. The solutions were: tap water, salt water, baking soda, Comet cleanser, vinegar, and a freshly squeezed lime. The only solution they had to be careful with was the Comet cleanser, everything else was harmless.
Each lab tray had the following set up (1 tray had supplies for 4 people to share, but they worked in pairs):
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One 125 mL flask of cabbage juice with a pipette
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red litmus paper vial
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blue litmus paper vial
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12 clear plastic cups
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1 large paper/coffee cup for used pH paper
On the side of the classroom, I had the 6 containers of solutions with a pipette in each solution. I used small take out containers I had at home. I have a habit of saving all types of plastic containers instead of throwing them out. As a teacher, they come in handy! I was able to set some stuff up at home and just add water to make the solutions when I got to school. The tops were pretty secure so it was easy to transport.
To test the solutions, they only needed 3-4 pipettes full of each item placed into their cups. Back at their table, they tested using pH paper first, then added the cabbage juice. When using the cabbage juice, 3-4 pipettes full was plenty to observe the color change.
They were able to complete this activity within one class period. The red cabbage juice has a strong smell, which they were all to happy to comment about it! =) I made the cabbage juice at home using half a head of red cabbage and boiling it for about 45 minutes to get a dark purple color. Once it cooled, I placed it into an empty soda bottle and filled it up about 95%. I added a small amount of rubbing alcohol to the bottle. This helps to keep it fresher longer and stop it from getting rancid too quickly. The rubbing alcohol does not change the properties of the cabbage juice or affect the pH. You can refrigerate it if you want to keep it longer as well.
Notebook:
Thanks for the tip on adding alcohol to the cabbage juice – I am getting ready to a similar lesson with my students. Your blog and website are so helpful – thank you for sharing.
Great Lab. Again, I use the GEMS Guide: Of cabbages and chemistry. It’s another great resource.
http://lawrencehallofscience.stores.yahoo.net/ofcabandchem.html
As an assessment, I use this flash game, it’s a fun game (Alien Juice Bar PH)
http://sv.berkeley.edu/showcase/flash/juicebar.html