Question

State True or False.
Addition and shaking of ${{I}_{2}}$ crystals turn $KBr$solution violet.
(A) True
(B) False

Answer 1

Hint: Iodine lies below bromine in the 17th group of the modern periodic table. We have studied earlier that a halogen can reduce the elements below its position in the respective group. Try writing the reaction of ${{I}_{2}}$ with $KBr$and analyse if a chemical reaction is possible or not.

Complete step by step answer:
Fluorine, Chlorine, Bromine and Iodine belong to the 17th group of the modern periodic table. The modern periodic table was given by Henry Moseley in the year 1932.
The 17th group is commonly referred to as the halogen group. All the elements of the 17th group act as good oxidising agents. They have a general configuration of $n{{s}^{2}}n{{p}^{5}}$.
Although the elements of the halogen group are considered as good oxidising agents, their oxidising tendency is not the same. Fluorine is considered the most powerful oxidising agent and iodine the least powerful.
As mentioned in the hint above, fluorine can oxidise the elements below it in the group i.e. chlorine, bromine and iodine. In the same way, bromine can oxidise iodine. However, iodine cannot oxidise bromine ions.
Hence when iodine crystals are added to potassium bromide solution, there is no chemical reaction taking place. The solution takes the colour of iodine crystals. The colour of the solid is deep purple
.
Therefore, the statement: Addition and shaking of ${{I}_{2}}$ crystals turn $KBr$solution violet is true.

Note: One of the most common uses of iodine is to check the presence of starch in a given substance. A solution of iodine and potassium iodide that is orange-brown in colour turns purple when it comes in contact with starch molecules. The compound in starch responsible for the colour change is amylose which is a long linear chain.