Student Science Experiments
All of the experiments must be done in the presence of a parent or teacher.
Experiment 5: Chemistry Colors - Mix and Match
Sometimes when scientists do an experiment, such as a chemical reaction, they may be very interested in the colors produced during the reaction. Scientists may need to observe the color very closely to compare it with another color. In the activity below, you can use your powers of observation to try to create an exact color match using a chemical reaction.
Note: All experiments should be done using original formula effervescent Alka-Seltzer.
- Three clear plastic bags
- Red cabbage
- Lemon juice
- Baking soda
- Small cups (for lemon juice and baking soda)
- Flat toothpick
- Zip-closing plastic bag
- Masking tape
- Tear up two or three red cabbage leaves into small pieces. Place the pieces into a zip-closing plastic bag. Add one cup of warm water to the bag and seal it tightly.
- Squeeze the leaves in the bag until the water turns a dark blue color. This is your indicator solution. An indicator can change color when certain substances are added to it. Use masking tape and a pencil to label two of your cups A and B. Pour 1/4 cup of the indicator into each of the two cups.
- In a separate cup, add 1/4 cup of water. Place one Alka-Seltzer tablet in the water. Wait for the tablet to dissolve completely. Use your straw to place five drops of Alka-Seltzer solution into cup A. Swirl the cup. What do you see? How does the color in cup A compare with the color is cup B?
Look at the ingredients on the package of Alka-Seltzer. Aside from aspirin, the ingredients are sodium bicarbonate and citric acid. Sodium bicarbonate is baking soda, and citric acid is the acid in citrus fruits such as lemons and oranges.
CHALLENGE! See if you can add the right amounts of lemon juice and baking soda to the indicator in cup B to produce the exact color that the five drops of Alka-Seltzer solution produced in cup A. Here's how to do it!
Add one drop of lemon juice to the indicator solution in cup B. Swirl the cup. If this does not match the color of the solution in cup A, use your toothpick to add a small amount of baking soda to cup B and swirl again. Keep track of the exact amounts of lemon juice by drops and baking soda by toothpicks you are adding. Observe the colors in the two cups very closely.
- When you think you know the right amounts of lemon juice and baking soda, rinse out cups A and B to get ready to test your results. Place 1/4 cup of indicator in cups A and B. Add five drops of Alka-Seltzer solution to cup A as before, and swirl. All at once, add the exact amount of lemon juice and baking soda that you think will match the color in cup A, and swirl. How did you do?