Question

The solution of ${H_2}{O_2}$ can be stored for a long time at room temperature. However, bubbles of oxygen form as soon as a drop of bromine is added. The role of bromine for the reaction is:
 $2{H_2}{O_2}(aq) \to 2{H_2}O + {O_2}$
A.to act as a positive catalyst
B.to form an intermediate \[\left( {Br - } \right)\] on reacting with ${H_2}{O_2}$ following reduction of bromine and then to show oxidation of $B{r^ - }$ to$Br$ by ${H_2}{O_2}$
C.to act as heterogeneous catalyst
D.to act as negative catalyst \[B{r_2}\]

Answer 1

Hint: Hydrogen peroxide in its pure for, is a blue liquid slightly more viscous than water. It is prepared by the electrolysis of $30\% $ ice cold ${H_2}S{O_4}$ .Bromine acts as a catalyst in various reactions. It forms an intermediate $(B{r^ - })$ on reacting with ${H_2}{O_2}$ .

Complete step by step answer:
In the decomposition of hydrogen peroxide, two successive reactions of with ${H_2}{O_2}$ bromide and then with bromine, takes place.
Because these two reactions together serve as a catalytic pathway for hydrogen peroxide decomposition, both of them must have significantly lower activation energies than the uncatalyzed decomposition.
Hence, bromine acts as a negative catalyst in the reaction.
Further, it forms an intermediate on reacting with ${H_2}{O_2}$ following reduction of bromine and then show oxidation of \[B{r^-}\] to by ${H_2}{O_2}$
 ${H_2}{O_2}$ Slowly oxidizes bromide into elemental bromine. The late two form a tribromide that exhibits a characteristic 272-nm absorption peak.
 $2Br(aq) + {H_2}{O_2}(aq) + 2H(aq) \to B{r_2}(l) + 2{H_2}O$

Hence, option B and D both are correct.

Note:
Hydrogen peroxide should be stored in roofed, fireproof rooms where it can be kept cool and protected from direct sunlight.
The catalyst potassium iodide solution decomposes hydrogen peroxide most rapidly.