Although pH paper won't break the bank, it is easy to make a pH indicator solution (or paper) from supplies you can get at your local grocery. What you need:
- red cabbage
- filter paper or coffee filters
- boiling water
I've taken a lot of photos, because red cabbage is absolutely beautiful! But really, making the solution as easy as boiling a cabbage and using the water as the indicator!
Steps to Make Cabbage Indicator Solution
- Dice 1/2-3/4 of a cabbage into small pieces and enjoy the beautiful color.
2. Boil water in the microwave or on the stove.
3. Pour boiling water over the cut cabbage and allow to steep until room temperature.
4. Strain cabbage through a strainer so only the purple liquid remains. You may chose to filter the cabbage/water solution through a coffee filter in addition to straining.
5. Reserve the purple liquid for experimentation. I store my excess cabbage juice in an empty plastic peanut butter container with a tight lid.
Labs Using Cabbage pH Indicator
Its best to set students up to experience the whole pH spectrum. While you could TELL them about the differences between acids and bases, I believe its best to let them experience the color changes in an inquiry-based lab, and allow them ask questions naturally, so they actually want to know why there are differences.
Therefore, I suggest providing students with the following materials to test and record:
- lemon juice
- white distilled vinegar
- baking soda
- washing soda (or ammonia)
Start the laboratory experience by determining the scope of the pH scale. You do this by using the materials listed above.
Pour the cooled cabbage indicator solution into test tubes or small jars. We used glass baby food jars which worked great because they don't tip easily, and any color change is easily noticeable. So we poured cabbage juice (which does have an odor you will notice) into each of the 5 jars. Then we created a data table that looked like this. However, I provide a free student lab sheet at the bottom of this post if you want something quick.
Since I am working with a five-year old, I made the table, and had colored pencils and crayons available for him to use to record data. He poured, squeezed, and dabbled the lemon juice, vinegar, water, baking soda, and washing soda, into the baby food jars one at a time and got amazingly different results; visible by stark color differences.
FYI: crayons were great to use, Caleb, my 5-year old could look at the solution, and search for a crayon that matched, and use that to fill in his data table. The goal here was to create a scale on which we could base all of the miscellaneous tests we wanted to do.
Here is what our baseline comparison tests look like:
- Lemon Juice = pink
- Vinegar = red
- Water = no change, purple
- Baking soda = blue
- Washing soda = green
- Bleach or drain cleaner = yellow/white
We had all our baby food jars all lined up in order from lowest (acid) to highest (base) and then began our own testing sessions. I had Caleb choose items and then predict whether he thought it would be acidic like lemon juice, neural like water, or basic like washing soda. That made it a game and kept us moving through the activity (Disclaimer: I've cropped out the Lego Minifigures that were a constant distraction throughout the lab...)
Once we had our baseline pH jars set up, we picked items from the refrigerator, cabinet, and bathroom to compare. I poured the sample solutions we wanted to test into the test tubes, and had my son use a dropper to add the cabbage indicator solution. We were not picky about how many drops etc...but if you teach older kids, keeping volumes constant is a good idea.
Additional Materials to have on hand:
- Test tubes (not essential, but cool)
- lab notebook and pencil
- milk = purple = neutral
- canned mandarin orange syrup = pink = acid
- bleach = white = base (off our scale, completely removed the purple)
- window cleaner = green = base
- liquid soap = pink = acid
Other ideas of items to test (but allow your kids make the final decision):
- cream of tartar
- soapy water
- salty water
- oven cleaner
- cleaning solutions
- soda (pops) clear is better
- oranges/orange juice
NOTE: Some of these suggested materials are dangerous. Make sure the children know the dangers of the chemicals, and handle them with care.
I'm not usually about going out and buying items you'll only use once or twice, but I couldn't believe the difference it made to have test tubes for this lab! We've used baby food jars before, and I guess they aren't that impressive to a 5 year old. But when he saw the test tubes, in a holder, with rubber stoppers, he was "all about" the science experiment. (He even tried to make a white lab coat by taping together computer paper...cute right?) He couldn't wait to pour liquids into and out of these narrow tubes. He also was super excited about the droppers (that I got for free). So I guess what I am saying, is that you would consider having these "science-y" things around so kids feel more like a real scientist.
Storage of Cabbage pH Indicator
I have poured the excess cabbage juice pH indicator solution into an empty plastic peanut butter container. I will update you as to how well the indicator does over time. (You need to read my update, because storing the cabbage solution in plastic does NOT work.) And the DIY pH papers can be stored in a paper envelope, as long as the envelope is kept dry and out of light. I have posted a tutorial on how to make the pH papers, which will make storage a bit easier.
I've made a student worksheet to accompany this lab. It would work for elementary and middle level.
Resources for Cabbage pH Lab
I believe this YouTube video Using Cabbage as a pH indicator was done by a couple of college kids, and does a good job of showing how to make the indicator, as provide in real-time examples of the purple changing colors along the entire pH spectrum.
Science Buddies: Describes how to use cabbage (and other plant materials) as indicators.
You can even make pH filter paper that function like the pH papers you would buy at a science supply store.
If you like this post on pH: you'll like the posts I've done since:
DIY pH Paper using Cabbage Juice and Coffee Filters
Baseline pH Scale to Use on the Field
Dr. Darci the STEM Mom