Question

Starch is used as a best indicator in iodometric titration because:
(A) it easily forms a complex with iodine
(B) it is readily available
(C) it is non-toxic
(D) all of these

Answer 1

Hint: For this problem, we have to first study the iodometry titration and where it is used. Then we will determine the use of the indicator and its type that is used in the process. After which we can easily determine the correct option.

Complete step by step solution:
-In the given question, we have to choose the correct option regarding the starch which is considered as the best indicator in the iodometric titration.
-The iodometric titration is also known as iodometry in which the concentration of the oxidising agent can be determined with the help of iodine in water.
-This method is also used to determine the volume of active chlorine in the swimming pools.
-Now, in this process starch is considered as the best indicator due to its insolubility because when we add starch in the iodine solution then it forms a blue-black colour starch iodine complex.
-The net reaction of iodometry will be:
$\text{I}_{3}^{-}\text{ + 2}{{\text{S}}_{2}}\text{O}_{3}^{-2}\text{ }\to \text{ }{{\text{S}}_{4}}\text{O}_{6}^{-2}\text{ + 3}{{\text{I}}^{-}}$
-The addition of starch helps us to easily identify the presence of iodine in the solution.
-Now, also it is easy to prepare the starch solution in the laboratory by adding 1 gram starch such as corn or potato into 10 ml of distilled water.
-So, it is one of the most easily available solutions to be used in various experiments.
-Moreover, the starch solution is also not toxic and is harmless.
-So, we can say that given all the options about the starch to be the best indicator are correct.

Therefore, option (D) is the correct answer.

Note: The starch solution which is used as an indicator should be freshly prepared because if it is an old solution it will be decomposed and the sensitivity of the solution will decrease. Due to which the results were not accurate.