Question

Name and state in brief the process which is used to prepare sodium hydroxide from sodium chloride. In this process along with the main product two gases ‘X’ and ‘Y’ are also given off at the two electrodes. Name ‘X’ and ‘Y’ specifying the name of their respective electrode at which each gas is obtained. One of these gases when reacts with dry calcium hydroxide produces a compound ‘Z’ which is widely used in water treatment plants and textile industries. Name Z and write chemical equation for the reaction involved in its formation.

Answer 1

Solution: In the Chlor-alkali process, sodium chloride (NaCl) is electrolyzed to produce sodium hydroxide (NaOH), chlorine gas (Cl$_2$), and hydrogen gas (H$_2$):
\[2\text{NaCl (aq)} \xrightarrow{\text{electrolysis}} 2\text{NaOH (aq)} + \text{Cl}_2\text{(g)} + \text{H}_2\text{(g)}\]
- Chlorine gas (Cl$_2$) is liberated at the anode.
- Hydrogen gas (H$_2$) is liberated at the cathode.  
When chlorine reacts with dry calcium hydroxide (Ca(OH)$_2$), calcium hypochlorite (Ca(OCl)$_2$) is formed:
\[\text{Ca(OH)}_2\text{(s)} + \text{Cl}_2\text{(g)} \rightarrow \text{Ca(OCl)}_2\text{(s)} + \text{H}_2\text{O(l)}\]
Calcium hypochlorite is used in water treatment and the textile industry for bleaching purposes.