Question

Identify the correct statement regarding the following chemical reaction.
\[\text{HI (aq) + C}{{\text{l}}_{2}}\text{ (aq) }\to \text{ }{{\text{I}}_{2}}\text{ (s)}\text{ + 2HCl (aq)}\]
(A) Iodine in HI is reduced and chlorine is oxidized.
(B) Iodine in HI is oxidised and chlorine is reduced.
(C) Both iodine in HI and chloride are reduced.
(D) Both iodine in HI and chloride are oxidized.

Answer 1

Hint: Oxidation is the gain of oxygen and loss of electrons whereas reduction is the loss of oxygen and gain of hydrogen as well as electrons. Increase in oxidation state occurs due to the loss of electrons.

Complete step by step answer:
-Oxidation and reduction reaction can be determined with the help of an oxidation state.
-Iodine has a valency -1 whereas chlorine also has a valency of -1 because both are halogens but their oxidation states are different in a molecule.
-From the above reaction, we can calculate the oxidation state of iodine in HI and \[{{\text{I}}_{2}}\].
-Let the oxidation state of Iodine is 'x' and we know that oxidation state of hydrogen is 1, so the value of x will be:
$\begin{align}
  & \text{1 + x = 0} \\
 & \text{x = -1} \\
\end{align}$
-Therefore, the value of x or the oxidation state of iodine is -1.
-Whereas the oxidation state of chlorine in $\text{C}{{\text{l}}_{2}}$is 0 and in HCl, we can calculate the oxidation state of chlorine by assuming it as 'x'.
-Let the oxidation state of chlorine is 'x' and we know that oxidation state of hydrogen is 1, so the value of x will be:
\[\]$\begin{align}
  & \text{1 + x = 0} \\
 & \text{x = -1} \\
\end{align}$
-Therefore, the oxidation state of chlorine is -1.
-So, we can observe clearly that the oxidation state of Iodine is increasing whereas that of chlorine is decreasing.
-We know that oxidation occurs when there is an increase in the oxidation state and reduction takes place when there is a decrease in the oxidation state.

Therefore, Iodine in HI is oxidised because of the increase in the oxidation number and chlorine is reduced because of the decrease in the oxidation no. Hence, the correct option is (b).

 Note: One should always keep in the mind, all the rules for calculating the oxidation state. Like a single element has zero oxidation state and calculates the oxidation state in a molecule we consider the unknown oxidation state as 'x'.