JEE MAIN - Chemistry (2023 - 29th January Evening Shift - No. 13)
An indicator 'X' is used for studying the effect of variation in concentration of iodide on the rate of reaction of iodide ion with $$\mathrm{H_2O_2}$$ at room temp. The indicator 'X' forms blue coloured complex with compound 'A' present in the solution. The indicator 'X' and compound 'A' respectively are :
Methyl orange and $$\mathrm{H_2O_2}$$
Methyl orange and iodine
Starch and $$\mathrm{H_2O_2}$$
Starch and iodine
Explanation
The indicator 'X' is starch, and it forms a blue colored complex with iodine (compound 'A'). Therefore, the correct option is:
Option D: Starch and iodine
In this situation, starch is commonly used as an indicator to detect the presence of iodine because starch forms a deep blue complex with iodine. This color change is visible and helps in monitoring the progress of the reaction involving iodide ions and hydrogen peroxide, which ultimately produces iodine. The blue color indicates the presence of iodine in the solution.
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