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This clock reaction uses sodium, potassium or ammonium persulfate to oxidize iodide ions to iodine. Sodium thiosulfate is used to reduce iodine back to iodide before the iodine can complex with the starch to form the characteristic blue-black color. Iodine is generated: 2 I − + S 2 O 2− 8 → I 2 + 2 SO 2− 4. And is then removed:
Note that iodometry involves indirect titration of iodine liberated by reaction with the analyte, whereas iodimetry involves direct titration using iodine as the titrant. Redox titration using sodium thiosulphate, Na 2 S 2 O 3 (usually) as a reducing agent is known as iodometric titration since it is used specifically to titrate iodine. The ...
Sodium thiosulfate (sodium thiosulphate) is an inorganic compound with the formula Na 2 S 2 O 3 ·(H 2 O) x. Typically it is available as the white or colorless pentahydrate (x = 5), which is a white solid that dissolves well in water. The compound is a reducing agent and a ligand, and these properties underpin its applications. [2]
A bottle of iodine solution used on apples to determine the correct harvest time. The chart shows the level of residual starch. The cut surface of an apple stained with iodine, indicating a starch level of 4–5. The iodine–starch test is a chemical reaction that is used to test for the presence of starch or for iodine. The combination of ...
The reaction involves the formation of a bromonium intermediate as follows: [7] Bromination of unsaturated fats. Then the unused bromine is reduced to bromide with iodide (I −). + + Now, the amount of iodine formed is determined by back-titration with sodium thiosulfate solution.
In an iodine clock reaction, colour changes after a time delay.. A chemical clock (or clock reaction) is a complex mixture of reacting chemical compounds in which the onset of an observable property (discoloration or coloration) occurs after a predictable induction time due to the presence of clock species at a detectable amount. [1]
These salts are often generated by oxidation of thiosulfate. For example, tetrathionate is obtained by oxidation of thiosulfate ion with iodine (reaction is used in iodometry): S 2 O 2− 3 + I 2 → S 4 O 2− 6 + 2 I −. More specialized routes involve reactions of sulfur chlorides with bisulfite salts: SCl 2 + 2 HSO − 3 → [O 3 SSSO 3] 2 ...
As an alternative, ascorbic acid can be treated with iodine in excess, followed by back titration with sodium thiosulfate using starch as an indicator. [40] This iodometric method has been revised to exploit the reaction of ascorbic acid with iodate and iodide in acid solution. Electrolyzing the potassium iodide solution produces iodine, which ...