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When starch reacts with iodine, why does it create the
characteristic blue-black colour?
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Answer / naval
IT IS THE CARBOHYDRATE TEST.POLYSACHHARIDIDE GIVES THIS
TEST.STARCH IS POLYSACCHARIDE.
| Is This Answer Correct ? | 21 Yes | 7 No |
Answer / tejaswini.b
Amylose in starch is responsible for the formation of a deep blue color in the presence of iodine & iodine molecule slips inside of the amylose coil. Iodine is not very soluble in water, iodine reagent is made by dissolving iodine in water in the presence of potassium iodide. This makes a linear triiodide ion complex which is soluble that slips into the coil of starch causing an intense blue/black color.
| Is This Answer Correct ? | 2 Yes | 2 No |
Answer / gurudut
Light is reflected or absorbed according to the shape and
form of the molecular complex it enters.
It so happens that the amylose helix with iodine ions in
the helical core is totally absorptive of all the longer
wavelengths of visible light. Colour is only reflection of
particular wavelengths.
The starch iodine test was selected for the entirely
fortuitous reason that it is so diagnostic for chance
reasons alone.
Evidence of the structural nature of the colour lies in
showing that a heated solution of starch-iodine complex
loses its colour at about 70?C and regains it again on
cooling i.e. the amylose denatures and renatures again.
| Is This Answer Correct ? | 19 Yes | 20 No |
Answer / mallikarjun
This reaction starts from a solution of hydrogen peroxide with sulfuric acid. To this is added a solution containing potassium iodide, sodium thiosulfate, and starch. There are two reactions occurring in the solution.
In the first, slow reaction, the triiodide ion is produced .
H2O2(aq) + 3 I−(aq) + 2 H+ → I3 + 2 H2O.
In the second, fast reaction, triiodide is reconverted to iodide by the thiosulfate.
I3(aq) + 2 S2O32−(aq) → 3 I−(aq) + S4O62−(aq)
After some time the solution always changes color to a very dark blue, almost black.
When the solutions are mixed, the second reaction causes the triiodide ion to be consumed much faster than it is generated, and only a small amount of triiodide is present in the dynamic equilibrium. Once the thiosulfate ion has been exhausted, this reaction stops and the blue color caused by the triiodide – starch complex appears.
| Is This Answer Correct ? | 2 Yes | 4 No |
Answer / guest
because you send iodine thats why it react blue black colour
| Is This Answer Correct ? | 0 Yes | 5 No |
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