Question

$NaOCl$ is used as a bleaching agent and sterilising agent. It can be prepared by the action of:
A. $NaCl$ with ${{H}_{2}}O$
B. $N{{H}_{4}}OH$ with $NaOH$
C. \[C{{l}_{2}}\] with cold and dil. $NaOH$
D. chlorine​ with hot and conc. $NaOH$

Answer 1

Hint: Sodium hypochlorite is prepared by mixing a halogen gas, which means the halogen gas that acts as a bleaching agent with a strong base. The base should be cold and diluted as addition of hot and concentrated base give different products.

Complete Step by Step Answer:
Chlorine is a halogen element.
Chlorine gas on reaction with cold and dilute sodium hydroxide produces sodium hypochlorite which acts as a bleaching agent along with sodium chloride and water. The reaction can be given as follows:
$2NaOH+C{{l}_{2}}\to NaOCl+NaCl+{{H}_{2}}O$

In this reaction one mole of Chlorine gas in reaction with two moles of cold and dilute sodium hydroxide produces one mole of sodium hypochlorite which acts as a bleaching agent along with one mole of sodium chloride and one mole of water.

Chlorine gas on reaction with hot and concentrated sodium hydroxide produces sodium chlorate which does not act as a bleaching agent along with sodium chloride and water. The reaction can be given as follows:
$6NaOH+3C{{l}_{2}}\to Na{{O}_{3}}Cl+5NaCl+3{{H}_{2}}O$

In this reaction three moles of Chlorine gas on reaction with six moles of hot and concentrated sodium hydroxide produces one mole of sodium chlorate which does not act as a bleaching agent along with five moles of sodium chloride and three moles of water.
Thus the correct option is C.

Note: Sodium hypochlorite is highly used as a bleaching agent, sterilisation and preparation of antiseptic. It is a strong oxidising agent. The oxidation reactions of sodium hypochlorite are corrosive in nature.