9/13/2023 0 Comments Iodine clock reaction![]() The iodate in excess will oxidize the iodide generated above to form iodine: In this protocol, iodide ion is generated by the following slow reaction between the iodate and bisulfite: Adding more thiosulfate will have the opposite effect it will take longer for the blue color to appear.Īn alternative protocol uses a solution of iodate ion (for instance potassium iodate) to which an acidified solution (again with sulfuric acid) of sodium bisulphite is added. Increasing the pH, or the concentration of iodide or hydrogen peroxide will shorten the time. Once the thiosulfate ion has been exhausted, this reaction stops and the blue color caused by the triiodide - starch complex appears.Īnything that accelerates the first reaction will shorten the time until the solution changes color. When the solutions are mixed, the second reaction causes the triiodide ion to be consumed much faster than it is generated, and only a small amount of triiodide is present in the dynamic equilibrium. I 3 -(aq) + 2 S 2O 3 2-(aq) → 3 I -(aq) + S 4O 6 2-(aq)Īfter some time the solution will rapidly change color to a very dark blue, almost black. In the second, fast reaction, triiodide is reconverted to iodide by the thiosulfate. In the first, slow reaction, the triiodide ion is produced. ![]() There are two reactions occurring in the solution. To this is added a solution containing potassium iodide, sodium thiosulfate, and starch. This reaction starts from a solution of hydrogen peroxide with sulfuric acid. 3 Persulfate/Peroxydisulphate variation.Waste DisposalDispose all liquids down the drain with plenty of water.ĭig deeper into the science behind clock reactions in this paper from the Journal of Chemical Education. Be very careful not to spill any of the solution. Safety Precautionsīe careful when working with the iodine – it stains, and it stains really well. Once the Vitamin C is used up, the solution turns blue, because now the iodine element and starch are present. Now after a short time as the reactions keep proceeding in this fashion, the Vitamin C gets gradually used up. The net result, at least for part of the time is that the solution remains colorless with excess of iodide ions being present. BUT, before that can actually happen, the Vitamin C quickly reacts and consumes the elemental iodine. In Reaction # 1 iodide ions react with hydrogen peroxide to produce iodine element which is blue in the presence of starch. During these reactions two forms of iodine created – the elemental form and the ion form. There are actually two chemical reactions going on at the same time when you combine the solutions. Keep pouring the liquid back and fourth between the cups. Pour solution A into solution B, and pour the resulting solution back into the empty cup to mix them thoroughly.Prepare “solution B” by adding 2 oz of water to 3 tsp of hydrogen peroxide and 1/2 tsp of liquid starch solution. ![]()
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