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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 ...
The relevant reaction is akin to the iodine reaction: thiosulfate reduces the hypochlorite (the active ingredient in bleach) and in so doing becomes oxidized to sulfate. The complete reaction is: 4 NaClO + Na 2 S 2 O 3 + 2 NaOH → 4 NaCl + 2 Na 2 SO 4 + H 2 O. Similarly, sodium thiosulfate reacts with bromine, removing the free bromine from ...
(B – S) is the difference between the volumes, in mL, of sodium thiosulfate required for the blank and for the sample, respectively; N is the normality of sodium thiosulfate solution in Eq/ L; 12.69 is the conversion factor from mEq sodium thiosulfate to grams of iodine (the molecular weight of iodine is 126.9 g/mol);
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 ...
The brown precipitate then converts the iodide ion (I −) to iodine. The amount of dissolved oxygen is directly proportional to the titration of iodine with a thiosulfate solution. [ 1 ] Today, the method is effectively used as its colorimetric modification, where the trivalent manganese produced on acidifying the brown suspension is directly ...
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 ...