Question

When ${\text{C}}{{\text{l}}_{\text{2}}}$ reacts with NaOH in cold condition then oxidation number of chlorine changes from 0 to
A) -1
B) +1
C) -2
D) +2

Answer 1

Write the balanced redox reaction for ${\text{C}}{{\text{l}}_{\text{2}}}$ and NaOH in cold condition. Using the oxidation number rule, assign the oxidation number to all species containing chlorine and determine the change in oxidation number of chlorine.

Complete step by step answer:
In cold condition ${\text{C}}{{\text{l}}_{\text{2}}}$reacts with NaOH as follows:
${\text{C}}{{\text{l}}_{\text{2}}}({\text{g) + 2NaOH (aq)}} \to {\text{NaCl(aq) + NaOCl(aq) + }}{{\text{H}}_{\text{2}}}{\text{O(l)}}$
Now using the oxidation number rules determine the oxidation number of chlorine in ${\text{C}}{{\text{l}}_{\text{2}}}$, ${\text{NaCl}}$ and ${\text{NaOCl}}$.
According to the oxidation number rules, the oxidation number of an element in free state is always zero.
So, the oxidation number of Cl in ${\text{C}}{{\text{l}}_{\text{2}}}$ is zero.
According to the oxidation number rules, the oxidation number of alkali metals is +1 so in ${\text{NaCl}}$ the oxidation number of Na is +1 and the oxidation number of Cl is -1 and the oxidation number of oxygen is always -2 except in peroxide. In peroxide oxidation the number of oxygen is -1.
So, in ${\text{NaOCl}}$, the oxidation number of O is -2, Na is +1 and so the oxidation number of Cl is +1.
${\text{C}}{{\text{l}}_{\text{2}}}({\text{g) + 2NaOH (aq)}} \to {\text{NaCl(aq) + NaOCl(aq) + }}{{\text{H}}_{\text{2}}}{\text{O(l)}}$
Thus, the oxidation number of chlorine changes from 0 to -1 in ${\text{NaCl}}$ and changes from 0 to +1 in ${\text{NaOCl}}$.

Hence, the correct options are (A)-1 and (B) +1.

Note: In cold condition ${\text{C}}{{\text{l}}_{\text{2}}}$ reacts with NaOH and form ${\text{NaOCl}}$ while in the hot condition it gives ${\text{NaCl}}{{\text{O}}_{\text{3}}}$ as one of the products so write the reaction using correct reaction condition. The possible oxidation states of chlorine are -1, 0 and +1. Oxidation is the loss of electrons while reduction is the gain of electrons. During oxidation, the oxidation number of an atom increases while during the reduction oxidation number of an atom decreases.