You can mention that acidic substances, like orange juice or tomatoes, taste sour. Bases, like baking soda or soap, are bitter. This is also a good time to explain that some acids and bases are very strong and can be harmful. Battery acid and ammonia (a base) are two dangerous substances that may be encountered at home, for instance. Another activity might be to have the children draw or write the mane of some common acids and bases and then identify where they fall on the acid/base scale.
Bleach (13) Soapy water (12) Baking soda (9) Pure water (7) Black coffee (5) Lemon juice (2)
If the kids know a bit about atoms and molecules, but are new to the concept of ions, just explain that they are particles with a particular charge (positive or negative). You can also mention that acids and bases neutralize each other because mixing them changes the relative concentrations of positive and negative ions. So, if you add baking soda (a base) to vinegar (an acid), the mixture’s pH will move closer to 7 (the neutral point on the pH scale).
It doesn’t matter how much you pour in each cup. A few ounces will be fine, and should leave you enough experiment with several substances. Use as many cups as you have substances to test. For instance, if you want to test milk, tomato juice, and soy sauce, use three cups.
Explain the indicator solution changes this color because baking soda is a base.
Explain this is because the acidic vinegar changes the pH of the solution by neutralizing the base (baking soda).
To help the kids decide, ask them to think about whether or not the substance tastes sour (acid) or bitter (base).
