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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]
Sodium tetrathionate is formed by the oxidation of sodium thiosulfate (Na 2 S 2 O 3), e.g. by the action of iodine: [1] 2 Na 2 S 2 O 3 + I 2 → Na 2 S 4 O 6 + 2 NaI. The reaction is signaled by the decoloration of iodine. This reaction is the basis of iodometric titrations. Other methods include the coupling of sodium bisulfite with disulfur ...
A common example of a redox titration is the treatment of a solution of iodine with a reducing agent to produce iodide using a starch indicator to help detect the endpoint. Iodine (I 2 ) can be reduced to iodide (I − ) by, say, thiosulfate ( S 2 O 2− 3 ), and when all the iodine is consumed, the blue colour disappears.
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 ...
Tetrathionate is a product of the oxidation of thiosulfate, S 2 O 2− 3, by iodine, I 2: 2 S 2 O 2− 3 + I 2 → S 4 O 2− 6 + 2I −. The use of bromine instead of iodine is dubious as excess bromine will oxidize the thiosulfate to sulfate.
The Old Nassau reaction or Halloween reaction is a chemical clock reaction in which a clear solution turns orange and then black. This reaction was discovered by two undergraduate students at Princeton University researching the inhibition of the iodine clock reaction (or Landolt reaction) by Hg 2+, resulting in the formation of orange HgI 2.