Question

Oxidation number of Cl in $CaOC{{l}_{2}}$ (bleaching powder) is,
(a)- zero, since it contains $C{{l}_{2}}$
(b)- -1, since it contains $C{{l}^{-}}$
(c)- -1, since it contains $Cl{{O}^{-}}$
(d)- +1 and -1 since it contains $Cl{{O}^{-}}\text{ and }C{{l}^{-}}$

Answer 1

Hint: Bleaching powder is chemically known as calcium hypochlorite. It contains two hypochlorite ions. When dissolved in water only one is stable and the other ion decomposes.

Complete answer:
The chemical name of bleaching powder is Calcium hypochlorite.
It has a formula $Ca{{(OCl)}_{2}}$
It has a bleaching action or acts as a bleaching agent when it is in aqueous solution.
When chlorine gas is dissolved in lime water then there is a formation of calcium hypochlorite.
The reaction is given below:
$2C{{l}_{2}}+2Ca{{(OH)}_{2}}\to Ca{{(OCl)}_{2}}+CaC{{l}_{2}}+2{{H}_{2}}O$
Since bleaching action is only in the presence of water, it is dormant in the dry form, because the nascent oxygen is given only by water.
The bleaching powder has two hypochlorite ions, its structure is:
$(Cl{{O}^{-}})C{{a}^{2+}}{{(}^{-}}OCl)$
So, when it is dissolved in water, only one hypochlorite ion is active or decomposes to give nascent oxygen and chloride ion while the other hypochlorite ion is stable in the solution.
The reaction is:
$^{-}OCl+{{H}_{2}}O\to {{H}_{2}}O+C{{l}^{-}}+[O]$
So, the reaction of bleaching powder with water will be:
$Ca{{(OCl)}_{2}}+{{H}_{2}}O\to Ca(OCl)Cl+{{H}_{2}}{{O}_{2}}$
Since, there are two types of ions of chlorine we have to find the oxidation number of chlorine in both the ions:
The oxidation number of chlorine in $C{{l}^{-}}$ = -1
The oxidation number of chlorine in $Cl{{O}^{-}}\text{ = }x\text{ + (-2) = -1}$
$x\text{ = +1}$
So, there are 2 oxidation states of chlorine in $CaOC{{l}_{2}}$, -1 in $C{{l}^{-}}$ and +1 in $Cl{{O}^{-}}$

Hence the correct option is (d)- +1 and -1 since it contains $Cl{{O}^{-}}\text{ and }C{{l}^{-}}$

Note: The bleaching action of bleaching powder is due to the formation of nascent oxygen by hypochlorite ion. By oxidation, the nascent oxygen bleaches the colored substances.