In case you have a little chemist at home, a fun and fascinating project might be to teach him about acids and bases. Acids and bases are everyday substances, so it is easy to get children to identify with these concepts. You can talk about things that help children understand acids and bases (for example, the pH scale), but you can also make your own indicator at home, which you can use to have children try various substances and see if is that they are acidic or basic. Get creative and have a little fun experimenting!
Method 1 of 2: Explain the Properties of Acids and Bases
Step 1. Draw the pH scale
Get some paper and some markers or crayons and draw a long, thin vertical rectangle, drawing lines that divide it into 14 sections. Ask the children to color each of these sections a different color. Try to come up with a scale of colors that change gradually (for example, you can start with a light yellow in the bottom section and then change to yellow-orange, orange, red-orange, red, violet, purple, indigo, blue, greenish blue, etc.).
Step 2. Label the pH scale
Ask the children to label each section of the scale with a number in consecutive order, from 0 at the bottom to 14 at the top. Then write "Acids" near the bottom and "Bases" at the top, explaining that the numbers 0 to 6, 9 correspond to acids, 7 is neutral and 7, 1 to 14 correspond to bases..
Step 3. Talk about common acids and bases
Explain that acids and bases can be found everywhere. For example, bodies use acids as a way to help digest food, and there are many cleaning products that contain bases. You can ask the children to name some common substances and guess if they are acidic or basic.
- You can mention that acidic substances (for example, orange juice or tomatoes) taste sour, while bases (for example, baking soda or soap) are bitter.
- This is also a good time to explain that there are some acids and bases that are very strong and can be harmful. For example, two hazardous substances that could be found in the home are sulfuric acid and ammonia (a base).
- As another activity, you can ask the children to draw or write the names of some common acids and bases and then identify where they are found on the scale of acids and bases.
Step 4. Explain what the scale shows
Tell children that there are some substances that are acidic and some that are basic, and the pH scale helps people determine the potency of these substances. Point out that many common substances are acids or bases and mark them on the scale. Here are some common substances and their pH levels:
- bleach (13)
- soapy water (12)
- baking soda (9)
- pure water (7)
- black coffee (5)
- lemon juice (2)
Step 5. Talk about the chemistry behind acids and bases
If the children are more advanced and know some chemistry, you can explain that bases produce negative hydroxide ions (OH-) and that acids produce positive hydrogen ions (H +). The higher the concentration of H + ions, the stronger the acid (and vice versa).
- In case the children know something about atoms and molecules but the concept of ions is new to them, you can just explain to them that there are particles that have particular charges (positive or negative).
- You can also mention that acids and bases neutralize each other, since mixing them changes the relative concentration of positive and negative ions. Therefore, adding baking soda (a base) to the vinegar (an acid) will bring the pH of the mixture closer to 7 (the neutral point on the pH scale).
Method 2 of 2: Experiment with an indicator
Step 1. Make some red cabbage juice
Cut a head of red cabbage into thin strips and simmer for 30 minutes in enough water to cover the strips. Then, strain the juice, store it in another pot, and let it cool.
Step 2. Pour some of the juice into clear glasses
Explain that purple cabbage juice is known as an "indicator," meaning it will help them determine whether a substance is acidic or basic. Pour some of the juice into several clear glasses and reserve the rest for now.
- It doesn't matter how much you pour into each glass. A few milliliters will be fine, so you should have enough to experiment with various substances.
- Use the same number of glasses as the substances you are going to test. For example, if you want to try milk, tomato juice, and soy sauce, you should use three glasses.
Step 3. Add baking soda to the solution
Pour a tablespoon of baking soda into one of the glasses. Ask one of the children to stir until the baking soda begins to dissolve. The solution will change color from red to blue or purple.
Explain that the indicator solution turns that color because the baking soda is a base
Step 4. Pour vinegar into the solution
Pour some regular white vinegar into the same glass as the baking soda and ask one of the children to stir the solution, which will turn red before your eyes.
Explain that this is because the acidic vinegar changes the pH of the solution, neutralizing the base (the baking soda)
Step 5. Try adding different substances to the indicator solution
Practice adding different substances to the glasses that contain the solution. Drinks like cola, lemon juice, or milk work well. Before testing each substance, you can ask the children if they think the solution will turn bluish (which means it will be a base) or a more intense red (which means it will be an acid).