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 $2H_2{O}_2\left(aq\right)\to 2H_{2}O\left(l\right)+O_2\left(g\right)$ is :

• A. to act as a positive catalyst
• B. to form an intermediate $\left(B{r}^{-}\right)$ on reacting with $H_2{O}_2$ following reduction of bromine and then to show oxidation of $B{r}^{-}$ to $B{r}_2$ by $H_2{O}_2$
• C. to act as heterogeneous catalyst
• D. to act as negative catalyst

Answer 1

Answer: (B), (D)

The correct options are
B to form an intermediate $\left(B{r}^{-}\right)$ on reacting with $H_2{O}_2$ following reduction of bromine and then to show oxidation of $B{r}^{-}$ to $B{r}_2$ by $H_2{O}_2$
D to act as negative catalyst

In the decomposition of hydrogen peroxide, two successive reactions of $H_2{O}_2$, with bromide and then with bromine, take 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, as shown schematically in Figure.

Bromine acts as negative catalyst in the reaction. Bromine forms an intermediate $\left(B{r}^{-}\right)$ on reacting with $H_2{O}_2$ following reduction of bromine and then to show oxidation of $B{r}^{-}$ to $B{r}_2$ by $H_2{O}_2$.