One of our recent science lessons was on acids, bases and the pH scale. To help my kids grasp the difference between the two, and how to use the pH scale, we completed a few learning activities together.
You’ll find one of our favorites below, along with a FREE printable that will help your family complete their own experiments.
First, let’s review some of the basics.
What are acids and bases?
They are compounds you find everywhere, yet have very different properties.
When you put acids into water, you create a solution. During this reaction, the acid will actually release one of its protons, or Hydrogen ions (H+). This means that the positive and negative ions are no longer balanced, causing the solution to become acidic.
Common acid traits are:
- tasting sour
When a base is put into water, it accepts a proton, forming a Hydroxide ion (OH-).
Common traits of bases:
- slippery to the touch
As you can imagine, it’s important to know how acidic solutions are, so we know how to handle them. That’s where the pH scale comes in.
The scale ranges from 0 to 14 and solutions with a pH number less than seven are considered acidic (acids). Those with a pH number greater than seven are basic (bases/alkaline). If a solution happens to fall right in the middle, with a pH number of seven, it is neutral.
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Learning Activity to Determine pH Levels
To test the pH level of various household substances with your teen, you’ll need to start with an indicator, a compound that changes color depending on the pH level of the solution.
Make your own cabbage indicator
- Coarsely chop up red cabbage, place it in a pot, and cover it with water. The amount of cabbage you use will depend on how much liquid you’ll need for your experiments. I used a quarter of the cabbage and had plenty for three groups to do the following activity together.
- Cook the mixture over medium heat, long enough for the water to absorb the purple pigment from the cabbage (approximately 15 minutes).
- Strain the cabbage, reserving the liquid.
Testing Household Substances
First, create a visual baseline (for later comparison) by filling up three test tubes (or glasses) 1/4 full of cabbage indicator.
In the first one, mix in a dropper full of vinegar (a known acid), and watch the color turn red. The second one will stay straight cabbage indicator. In the third tube, add in some laundry detergent (a known base) and you’ll see the color turn green. Set them aside.
Then, print our FREE pH Testing Data Sheet for your student to use to record their findings.
- Milk of Magnesia
- Orange Juice
- Pickle Juice
- Tomato Sauce
- Window Cleaner
Just add a dropper full of the household substances you’ve chosen to a small amount of cabbage indicator and see what happens!
We learned all about the states of matter thanks to the Standard Deviants, found on Discovery Education.
Questions for your Teen to Ponder
- What do you notice about the acids and bases? Do they have anything in common?
- What occurred during the activity and why did it happen?
- Can you turn an acid or a base into a neutral? How?
After we were finished, the kids used the substances they tested to make their own pH scale, which they added to their science notebooks.