Cabbage Juice as an Indicator: An Update
I can't describe how tickled I am at how well the cabbage juice worked as a pH indicator. It was fun to make, and the results were visually stunning. (OK, my inner science geek is totally peeking through!) However, I have a confession and an update. The confession is that cooking cabbage will stick up the room. And the smell only gets worse the longer you store it! I've stored my juice in a plastic peanut butter jar, and the juice has wrecked havoc on the bottom of the plastic jar, as you can see from this photo, and started leaking the smelly juice. Therefore, I am warning you to store your cabbage juice in a glass container instead.
I've transferred my cabbage juice from a plastic container to a glass one. But notice in 4 days time, it is no longer purple, but pink. Hummmm....
Here's my update. After only four days, the cabbage juice has changed color from a deep purple, to a pink color, indicating that it is becoming more acidic. However, I ran my baseline test again, and it still works as an indicator. Therefore, storage long-term is probably not the best idea. If you want to use the cabbage juice indicator, you should mix it up only a day or so ahead of time, or better yet, have your (older) students make the solution the day they plan on using it. (I'll post a lab for older students later.)
Another solution to the liquid storage issue, is to use the cabbage juice to make your own pH paper. As usual, I took a lot of pictures, but it really is easy as just soaking coffee filters in cabbage juice.
Materials Needed for Making Your Own pH Paper
- 1/4-1/2 head of red cabbage
- rubber/latex/surgical gloves
- boiling water
- rubber spatula
- coffee filters
- shallow bowl or pan
- clothes line and pins
- paper envelope for storage of pH strips
Tutorial on How to Make Your Own pH Paper
The instructions for obtaining the cabbage juice is the same that I described in my previous tutorial on how to use cabbage juice as a pH indicator. The only difference is that you want the solution to be super concentrated. To extract as much as I could from this beautiful purple vegetable, I cut up about 1/4 head of cabbage and placed it in a blender. I only added enough water so the blender would chop it properly.
Oh, isn't is gorgeous? I'm not usually a big fan of purple, but man oh man, this is pretty.
Next, you'll want to strain the cabbage using a coffee filter lined-strainer. I had to use a rubber spatula to squeeze the liquid from the cabbage bits.
Once you've got the liquid isolated from the cabbage bits, you'll want to discard the bits and then take the garbage out. I've warned you that it smells, right? Reserve the beautiful purple liquid and place it in a shallow pan or bowl, and get your coffee filters ready. I used the cone shaped ones because we accidentally bought the wrong size, but I'm sure the fluted filters will work as well.
Next, wearing your rubber (latex) gloves (do as I say, not as I do), place your coffee filters into the cabbage juice and let them soak 2-3 minutes. The longer the better, don't rush this too much. You really want the juice to soak into the filters. I found that keeping the filters doubled like this photo made it so much easier to handle.
Next time I make my pH paper, I will use gloves, as I found that the parts of the filter I touched were not a neutral purple color. So I had to cut around these area when making my pH strips. More of the coffee filter will be usable pH paper, if you handle the filters with gloves.
Once the coffee filters have had a chance to soak, remove the filters, and set them somewhere to dry. Setting them on paper towels might be sufficient, but I hung mine on a clothesline I have in my laundry room for "Seeking Sole-Mates." (Great way to match up those missing socks/gloves that seem to get separated from their mates between loads.)
After the coffee filters have dried, get your scissors ready to transform the coffee filters into pH paper! Ah....what a wonderful thing.
Here's how I cut mine.
And that's really all there is to it! I wasn't real careful with how I cut the strips. My goal wasn't to pretend I'd bought the strips, so it was just a matter of getting as much as I could out of the coffee filter! Yes, I'm a cheap-skate.
Remember, store your cabbage juice in a glass container, not plastic (like I have in the photo below). The paper pH paper has done well being stored in the manilla envelope where I put them after being cut. I think this is the answer to our pH indicator storage issue. While the juice is not suited for long-term storage, the paper is. So once you've cooked up some red cabbage, you might as well, make a "batch" of pH paper. (Hey, maybe I should make a recipe card and put it on all recipes.com!)
For posterity's sake, I tested the pH paper and compared it to the cabbage indicator solution, and they match up perfectly. The colors are the same and therefore students will be able to approximate where on the pH scale a solution falls. While the paper work great, I still prefer the indicator solution, especially for younger kids. There's just something about the large volume of purple cabbage juice changing before your eyes. Using the pH paper will give you the same end product and color, but it seems so much less dramatic to me, and to the 5 year old!
However, the paper pH paper is so much more handy to take with you on a hike, to test pH as you go! Traveling with liquid is not convenient! Do let me know if you use these cabbage pH testing ideas! Would love to know we brought chemistry to you, your students, and your family.
If you liked this post, check out my other posts:
Cabbage Indicator Tutorial and Labs
pH Baseline Table to Use on the Field
I got the idea to make pH paper from Anne Marie Helmenstine, Ph.D., in an article she wrote about making pH paper.