Before we move on to the activity, you must understand the reaction that will occur. The reason that your liquid will turn from clear to blue is because the substances involved cause a chemical reaction. That reaction makes all the difference! Otherwise, there would be NO WAY that two clear liquids would make blue! (For a review of chemical reactions, visit our blog about the reaction between vinegar and baking soda).
The reaction that we are working with today is called an Iodine Clock Reaction. You will be using iodine, starch, and Vitamin C to create this reaction. The starch is trying to turn the iodine blue, but the Vitamin C is battling the starch. This causes a delay in the reaction. Eventually, the starch defeats the Vitamin C and the color change occurs.
The delay is the reason it’s called a clock reaction. Initially, when the two liquids are mixed, nothing happens. It takes a certain amount of time for the reaction to occur, and then BAM! Your liquid will suddenly change colors!
Check out this video of the reaction that you will be creating:
* Iodine tincture (2% from the pharmacy)
* Vitamin C tablet (1000 mg)
* Hydrogen peroxide (3% from the pharmacy)
* Liquid laundry starch
* 3 clear plastic cups
* Measuring spoons and measuring cups
Here’s what to do!
1. Label your cups A, B, and C.
2. Put a 1000mg Vitamin C tablet into a plastic bag and crush it up. You could use any hard object to help you crush it into a fine powder.
3. Carefully dump your Vitamin C powder into cup A. Add 2 ounces of warm water into the cup and stir until the powder is dissolved. Observe: What color is liquid A? What does it look like?
4. Before the next step, take a look at the iodine. What color is it?
5. Put one tablespoon of liquid A into the cup labeled B. Add one teaspoon of iodine. What happens to the color when these two liquids are mixed together? Set cup A aside.
6. Put 2 ounces of warm water into the cup labeled C. Add one tablespoon of hydrogen peroxide, then add 1/2 teaspoon of liquid starch. Use a spoon to stir the liquids together.
7. Now, let’s get going with this chemical reaction! Carefully pour the liquid in cup B into cup C. Pour the liquid back and forth between the two cups a few times and then wait patiently for a chemical color-changing surprise!
Extension: You just demonstrated an iodine clock reaction. How can you add a variable to create an experiment? Try changing the temperature of the water or the amount of Vitamin C or iodine to see if this affects the time it takes for the liquid to change colors! What about mixing? If you just let the liquid sit after you mix them, does it take longer to change? If you stir it more, does it change faster? Make sure to record your observations!