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At Discovery Place, we get to work with amazing animals every day. One of the ways our talented and passionate Aquarists care for these animals is by checking the pH level of the water in the aquarium tanks.
On a scale of acidity from 0 to 14, pH tells us how much free protons (also known as positive hydrogen ions) are in a substance. More acidic solutions have lower pH, between 0 and 6, and more free protons. More alkaline solutions have higher pH, between 8 and 14, and less protons. A pH of 7 is known as neutral and includes plain water.
Why does pH Matter?
The pH of a chemical can affect the way it behaves. One chemical that is particularly important to us humans is water. (Yes, water is a chemical). If the pH of a chemical in our body is too far from what it is supposed to be, it can affect the way our body functions.
The pH of water found in the environments of plants and animals, particularly marine life, can have a big impact as well. At Discovery Place, our team works diligently to ensure that the pH remains within the ideal range in our aquariums.
Make your own pH indicator
Today, we are going to show you how to create a pH indicator from red cabbage so you can test different chemicals around your house and get a sense of what the difference is between acidic and alkaline substances.
Red cabbage contains an indicator pigment molecule called flavin, which is a type of anthocyanin. This water-soluble pigment can also be found in apple skin, red onion skin, plums, poppies, blueberries, cornflowers and grapes. Very acidic solutions will turn anthocyanin a red color. Neutral solutions turn a purplish color. Basic solutions make a greenish-yellow or yellow color.
This activity will take approximately 30 minutes, with an additional 20 minutes of learning time.
It is best suited for children in elementary or middle school.
- Red cabbage
- Drinking glass
- Small white or clear cup
- Household test chemicals (lemon juice, pickle juice, vinegar, baking soda, raw egg, etc. )
- Measuring cup
- With help from an adult, cut red cabbage in small pieces. You only need enough cabbage to fill up a drinking glass (about 4-5 leaves). You can use the outside leaves or scraps.
- Put cut pieces in a bowl with 2 cups of boiling water. (Caution, boiling water is very hot. Have an adult help you with this step, too!)
- Let sit for 10 minutes
- Strain cabbage pieces out. (The leftover cabbage pieces can be a delicious snack, just add some salt, pepper and olive oil, or they can be put into a compost bin.)
- Once cool, put 1/4 cup of cabbage juice into your clear/white cup.
- Gather your test chemicals. Make a hypothesis. Predict what color change each liquid will cause. Which chemical do you think will be the most acidic? Which do you think will be the most alkaline (basic)?
- Add one to two teaspoons of one liquid (lemon juice, pickle juice, vinegar, etc.) to test. Compare to pH scale. Is your test acidic, neutral or alkaline?
- Repeat your test with a new test chemical. You can use a new cup or rinse out your previous test cup.
How to adjust for younger and older learners
For younger learners, use a blank piece of white paper as a canvas to paint with the cabbage juice and vinegar.
For older learners, use a coffee filter in the cabbage juice and allow to dry. Once dry, cut filter into strips and try testing other test chemicals (milk, soda, soap solution, etc.).
Is it going to rain soon? Collect some rainwater to test its pH! Make a hypothesis before you test. Will the solution be neutral? Acidic? Alkaline?
For all learners, be sure to use your leftover cabbage to make a delicious slaw to with tonight’s dinner. Now, that’s a yummy activity!
See a homemade pH indicator in action here:
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