"Egyptian night" experiment
How to make "Iodine clock" reaction
Egyptian night is a classic and very colorful experiment. Two transparent solutions are mixed, and after a while the resulting solution suddenly turns dark. Just as quickly as night falls in Egypt.
Reagents and equipment:
- potassium iodide;
- sodium thiosulfate;
- hydrogen peroxide;
- acid (sulfuric, acetic);
- two beakers;
- measuring glass;
- glass rod for stirring.
Mix approximately 0.2 g of starch and a small amount of cold water. Add a little hot water to dissolve the starch. Dilute the solution to approximately 800 ml. Add 50 g of potassium iodide and 10 g of sodium thiosulfate. Solution A is ready. Solution B is a mixture of 30% hydrogen peroxide, water with a small amount of acid (sulfuric, acetic etc.). This solution may be of any concentration – the reaction time depends on the concentration of hydrogen peroxide. Quickly mix solutions A and B. After some time, the solution obtained will suddenly turn dark blue.
In this experiment, three main reactions take place. The first is the slow reaction between hydrogen peroxide and iodine ions in the presence of H⁺ ions. As a result, molecular iodine forms. The second reaction is the swift reaction between iodine and sodium thiosulfate. This reaction leads to the formation of the triiodide ion, which is expended more quickly than it forms. When all of the thiosulfate reacts, this reaction stops and the triiodide ion forms a dark-blue mixture with the starch. The high concentration of H⁺ reduces the time it takes the color to change. Increasing the concentration of thiosulfatehas a reverse effect.
Wear protective glasses and gloves. Avoid the hydrogen peroxide and acids touching the skin and getting in the eyes or mouth. Follow general safety recommendations. Chemical experiments must be carried out in full compliance with the legislation of your country.
Warning! Substances of this experiment are toxic and highly dangerous for your health. Do not try this at home. Only under professional supervision.