If you have a little chemist at home, teaching him what acids and bases are is a fascinating and fun project. Since acids and bases are part of the substances we use every day, it is easy to simplify these concepts to expose them to a child. You can introduce information that helps your child understand acids and bases (such as the pH scale), but you can also make an indicator at home. Use it to have your child test various substances and check if they are acidic or basic. Leave room for creativity and have fun experimenting!
Steps
Method 1 of 2: Explain the Properties of Acids and Bases
Step 1. Draw the pH scale
Get a sheet of paper and markers or crayons. Draw a long thin vertical rectangle, divided by horizontal lines into 14 sections. Have the children use a different color for each section. Try to create a progressive color scale; for example you can start with light yellow at the bottom, then move on to orange, red, purple, blue, green etc.
Step 2. Add references to the stair
Ask the children to assign a progressive number to each section of the scale, from 0 to 14. Write "Acids" at the bottom and "Bases" at the top. Explain that values 0 to 6, 9 refer to acids, 7 is neutral pH, and 7, 1 to 14 refer to bases.
Step 3. Talk about the most common acids and bases
Explain that they are found everywhere. For example, our body uses acids to digest food and many detergents contain bases. Ask the children to name some common substances and to guess if they are acidic or basic.
- You can suggest that acidic substances, such as orange juice and tomatoes, are sour. The basic ones, on the other hand, such as baking soda or soap, are bitter.
- This is the right time to explain that some acids and bases are very powerful and can be dangerous. For example, almost everyone in the house has battery acid and ammonia (a base), two dangerous substances.
- You can also ask the children to draw or write the names of some common acids and bases, then specify where they are on the pH scale.
Step 4. Explain what the scale shows
Tell the children that some substances are acidic, others basic, and that the pH scale helps determine how strong they are. Explain that many common substances are acids and bases, then mark them on the scale. Here are some examples:
- Bleach (13).
- Soap and water (12).
- Baking soda (9).
- Pure water (7).
- Coffee (5).
- Lemon juice (2).
Step 5. Talk about the chemical laws of acids and bases
If the children are already well educated or have a smattering of chemistry, explain to them that bases produce negative hydroxide ions (OH–) and that acids produce positive hydrogen ions (H +). The higher the concentration of H + ions, the more powerful the acid (and vice versa).
- If the children are familiar with the concepts of atoms and molecules, but have never heard of ions, explain that they are particles with a particular charge (positive or negative).
- You can also explain that acids and bases neutralize each other, because mixing them changes the relative concentration of positive and negative ions. So, if you add baking soda (a base) to the vinegar (an acid), the pH of the mixture will approach 7 (the neutral point on the scale).
Method 2 of 2: Experiment with an Indicator
Step 1. Make some red cabbage juice
Take a red cabbage and cut it into fine strips. Let it simmer for 30 minutes completely immersed in water. Strain the juice through a colander and store it in another pot, then let it cool.
Step 2. Pour the juice into a clear glass
Explain that red cabbage juice is considered an "indicator", which is an element that helps you understand whether a substance is acidic or basic. Pour the juice into a few clear glasses. For now, keep the rest aside.
- It doesn't matter how much juice you pour into each glass. About 50 ml is enough and you will have enough to experiment with various substances.
- Use a glass for each substance to be tested. For example, if you want to test the pH of milk, tomato juice and soy sauce, use 3 glasses.
Step 3. Add the baking soda to the solution
Pour a tablespoon of baking soda into one of the glasses. Ask a child to mix until the powder dissolves. The solution will change from red to blue or purple.
Explain that the indicator takes on that color because baking soda is a base
Step 4. Pour the vinegar into the solution
Take regular white wine vinegar and pour it into the same glass with the baking soda. Ask a child to mix and the liquid will turn red before his eyes!
Explain that this happens because the acidity of the vinegar changes the pH of the solution, neutralizing the base (the baking soda)
Step 5. Try adding different substances to the indicator liquid
Experiment with mixing various liquids. You can pour drinks like cola, lemon juice, or milk. Before trying them, ask the child if he thinks the solution will turn blue (because a base is added) or even redder (due to the effect of an acid).
