Question

In one of the industrial processes used for the manufacture of sodium hydroxide, a gas $X$ is formed as a by-product. The gas $X$ reacts with lime water to give a compound $Y$ which is used as a bleaching agent in the chemical industry. Identify $X$ and $Y$, give the chemical equation of the reactions involved.

Answer 1

Part 1: Chlor-alkali process:

• The Chlor-alkali process is an industrial process in which electrolysis of Sodium chloride solution is done.
• Generally, this process is conducted on an aqueous solution of Sodium chloride$\left(\mathrm{NaCl}\right)$ which gives Sodium hydroxide$\left(\mathrm{NaOH}\right)$, Hydrogen, and Chlorine as products.
• The reaction of the Chlor-alkali process is as below,
  $\underset{\mathrm{Brine}\mathrm{solution}}{\underset{\mathrm{Sodium}\mathrm{chloride}}{2\mathrm{NaCl}\left(\mathrm{aq}\right)}+\underset{\mathrm{Water}}{2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}}\stackrel{\mathrm{Electrolysis}}{\to }\underset{\mathrm{Sodium}\mathrm{hydroxide}}{2\mathrm{NaOH}\left(\mathrm{aq}\right)}+\underset{\mathrm{Chlorine}}{\mathrm{C}{\mathrm{l}}_2\left(\mathrm{g}\right)}+\underset{\mathrm{Hydrogen}}{{\mathrm{H}}_2\left(\mathrm{g}\right)}$
• So, $X$ is chlorine gas.

Part 2: Chlorine reacts with lime water:

• When chlorine gas reacts with lime water or Calcium hydroxide, produces bleaching power and is utilized as a bleaching agent in the chemical industry.

$\underset{\mathrm{Chlorine}}{{\mathrm{Cl}}_2(\mathrm{g}})+\underset{\mathrm{Calcium}\mathrm{hydroxide}(\mathrm{Lime}\mathrm{water})}{\mathrm{Ca}{\left(\mathrm{OH}\right)}_2\left(\mathrm{s}\right)}\to \underset{\mathrm{Calcium}\mathrm{oxychloride}(\mathrm{bleaching}\mathrm{powder})}{{\mathrm{CaOCl}}_2\left(\mathrm{s}\right)}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}}(\mathrm{l})$

• So, $Y$ is Calcium oxychloride i.e. Bleaaching powder.

Therefore $X$ is Chlorine gas$\left({\mathrm{Cl}}_2\right)$ and $Y$ is Calcium oxychloride$\left({\mathrm{CaOCl}}_2\right)$.