Question

In the reaction of H2O2 and I- , a quantitative amount of S2O32- is added ;...

In the reaction of H2O2 and I- , a quantitative amount of S2O32- is added ; starch in solution is also added.

The balanced equation for the reaction is:

H2O2 + 3I- + 2H+ = I3- + H20

What is purpose of S2O32- ?

What is purpose of starch solution?

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Homework Answers

Answer #1

in an acidic solution, iodide ions are oxidized by hydrogen peroxide to I3- ions.

purpose of S2O3 2−

2 S2O32− (aq) + I3- (aq) -----> S4O62− (aq) + 3 I− (aq)

These triiodide ions are reduced back to iodide ions by thiosulfate ions and this reaction is faster than the oxidation of I2.

purpose of starch solution:

2 I3- (aq) + starch -----> starch-I5- complex + I- (aq)

after consuming of all the thiosulfate ions, triiodide ions react with starch to form the blue starch-pentaiodide complex.

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