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If you are a science teacher who wants to amaze your students, or just an average amateur chemist, then this is the experiment for you! The classic iodine clock reaction demonstrates the properties of chemical kinetics through its mesmerizing change in color, and it is sure to fascinate you and perhaps your audience. With just a few household items, you can easily perform this experiment with great success.
Steps
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Gather the materials. You will essentially need:- 10 volume hydrogen peroxide
- 1000 mg vitamin C tablets
- 5% Iodine tincture
- Distilled water
- Cornstarch
- Containers (preferably clear)
- Coffee filters
Prepare the first solution. Crush two of the vitamin C tablets with the back of a spoon until they are nearly powdery. Once that's done, put the powder into a container.Advertisement
Add 60 mL of distilled water to the container with the crushed tablets, and stir for 30 seconds. Don't worry if the powder doesn't completely dissolve — this is expected to happen.
Filter the solution using a coffee filter. It is necessary to get rid of the undissolved particles so that it doesn't interfere with the experiment. Once the filtration is complete, return the liquid to its original container.
Add 25 mL of the iodine tincture to the solution. You will notice that the iodine becomes colorless — this is because the elemental iodine from the tincture breaks up into ions, forming a colorless solution. (If your solution does not turn clear, it means that you didn't put enough vitamin C, and you will need to remake the solution.)
Add water to the solution until the total volume is 500 milliliters (16.9 fl oz). Your first solution is finished!
Prepare the second solution. Add a small amount of cornstarch to another container (around a teaspoon; the exact measurement isn't important).
Add 350 mL of distilled water to the container, mixing it with the cornstarch. Microwave the solution until it boils to dissolve as much cornstarch as possible. The solution may look cloudy, and you can filter it to get rid of the undissolved particles. However, this is optional, and is only done to demonstrate the experiment more clearly.
Add 150 mL of the hydrogen peroxide to the cornstarch solution. Your second solution is now complete.
Begin the reaction! To see the iodine clock reaction in action, mix an equal amount of the first solution and the second solution into a container (you do not need to use all of the solution). Within a minute or two, the liquid should suddenly turn into a dark color. The reaction is quite complex, but what is essentially happening is that the vitamin C is consumed, reverting the iodide ions to iodine molecules, which then react with the starch to form a bluish-black hue.
Have fun with the experiment! Try doing the reaction with different amounts, containers etc. Make some observations: Does the reaction occur faster at higher temperatures? Does the amount of solution used affect the reaction time? Will the mixture change color at the same time if you separated them into two containers?
Community Q&A
- QuestionWhat percent hydrogen peroxide should be used?
Community AnswerAccording to online sources, 10 volume hydrogen peroxide is the same as 3% hydrogen peroxide that you buy at the store. - QuestionWhat lf l want to use sodium thiosulphate?
Community AnswerSodium thiosulfate, also spelled sodium thiosulphate, is used as a medication to treat cyanide poisoning, pityriasis versicolor, and to decrease side effects from cisplatin. For cyanide poisoning it is often used after the medication sodium nitrite and typically only recommended for severe cases. Formula: Na2O3S2. - QuestionCan small doses of carbon monoxide be used in place of hydrogen peroxide?
HannahCommunity AnswerNo, it won't work. These two are completely different substances - one is a toxic gas and one is a liquid (at room temperature).
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Tips
- Your containers can be reused after the experiment. Wash them with a bit of dish soap, and they're good to go!Thanks
- This experiment can easily fail, so don't despair if your first attempt doesn't go as planned.Thanks
- If your vitamin C tablets or iodine tinctures are of a different concentration, then you will need to mathematically scale it to the correct ratio.Thanks
Warnings
- Iodine tinctures can stain clothing and skin, so avoid getting it on them.Thanks
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