Question

Boojho took some grains of boiled rice in test tube ‘A’ and Paheli took boiled and chewed rice in test tube ‘B’. Both of them poured 1 – 2 drops of iodine solution into the test tube and observed the color change. What color change would they have observed? Give reasons for your answer.

Answer 1

The iodine–starch test is a synthetic response that is utilized to test for the presence of starch or for iodine. The color of the blend of starch and iodine is strongly blue-black. The communication among starch and the triiodide anion is the reason for iodometry. The triiodide anion immediately creates an extraordinary blue-dark tone upon contact with starch. The power of the shading diminishes with expanding temperature and with the presence of water-miscible natural solvents like ethanol. The test can't be performed at exceptionally low pH because of the hydrolysis of the starch under these conditions. It is felt that the iodine–iodide combination consolidates with the starch to frame a limitless polyiodide homopolymer. This was defended through single gem X-beam crystallography and near Raman spectroscopy.

Complete answer:
In test-tube A, the bubbled rice contains starch. At the point when we add 1-2 drops of iodine, the mix turns in the shade of blue-dark. This shows the presence of starch in the test tube A.
In test-tube B, the starch of rice changes over into sugar on absorption. In this manner, the shade of iodine won't change.
Starch is regularly utilized in science as a pointer for redox titrations where triiodide is present. Starch frames a dull blue-dark complex with triiodide. In any case, the complex isn't shaped if just iodine or just iodide is available. The shade of the starch complex is profound to such an extent that it very well may be identified outwardly when the centralization of the iodine is pretty much as low as $20\mu M$ at $20^\circ C$.

Note:
We need to know that during iodine titrations, concentrated iodine arrangements should be responded with some titrant, frequently thiosulfate, to eliminate the majority of the iodine before the starch is added. This is because of the insolubility of the starch–triiodide complex which may forestall a portion of the iodine responding with the titrant. Near the endpoint, the starch is added, and the titration cycle is continued considering the measure of thiosulfate added prior to adding the starch. The shading change can be utilized to recognize dampness or sweat, as in the Minor test or starch–iodine test.