Question

In the reaction: $3B{r_2} + 6C{O_3}^{2 - } + 3{H_2}O\xrightarrow{{}}5B{r^ - } + Br{O_3}^ - + 6HC{O_3}^ -$
A.Bromine is oxidized and carbonate is reduced
B.Bromine is reduced and water is oxidized
C.Bromine is neither reduced or oxidized
D.Bromine is both reduced and oxidized

Answer 1

We can define redox reactions as chemical reactions in which transfer of electrons takes place between two reactants. We can identify the transfer of electrons by observing the change in oxidation states of the species that are reacting. Batteries (or) electrochemical cells are the examples of redox reactions.

Complete step by step answer:
The given chemical equation is,
$3B{r_2} + 6C{O_3}^{2 - } + 3{H_2}O\xrightarrow{{}}5B{r^ - } + Br{O_3}^ - + 6HC{O_3}^ -$
From the given chemical equation, we can see that bromine reacts with carbonate ion and water to form bromine anion/bromide ion, bromate ion and hydrogen carbonate/bicarbonate.
We can define oxidation reactions as loss of electrons from a substance.
Similarly, reduction reactions are defined as gain of electrons.
In order to identify the species that are oxidized and reduced, let us see the oxidation number of the elements in reactants and products.
In hydrogen, the oxidation number is +1 and in oxygen, the oxidation number is$- 2$.
For bromine, the oxidation number of bromine in $B{r_2}$ is $0$ and the oxidation number of $B{r^ - }$ is $- 1$. (Element in its free state will have zero as its oxidation number).
For bromine, the oxidation number of bromine in $B{r_2}$ is $0$ and the oxidation number of $Br{O_3}^ -$ is $+ 5$. (Element in its free state will have zero as its oxidation number).
For carbon, the oxidation number of carbon in carbonate anion is $+ 4$ and the oxidation number of carbon in bicarbonate/hydrogen carbonate is $+ 4$.
We can see that there is no change in the oxidation number of carbon, whereas the oxidation number of bromine has changed from $0$ to $- 1$ and $0$ to $+ 5$.
The oxidation reaction is written as,
$B{r_2}\xrightarrow{{}}Br{O_3}^ -$
The reduction reaction is written as,
$B{r_2}\xrightarrow{{}}B{r^ - }$
We can see that bromine is oxidized and reduced.

$\therefore$ Option (D) is correct .

Note:
We have in mind that Respiration, photosynthesis, combustion, rusting are some reactions. Oxidizing agents are that species (molecule/ion) that accepts electrons and reducing agents are species (molecule/ion) that donates electrons. A substance that is oxidized acts as a reducing agent and substance that is reduced acts as oxidizing agent.