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

Step 1: Process to prepare sodium hydroxide from sodium chloride:
The process used to prepare sodium hydroxide (NaOH) from sodium chloride (NaCl) is called chlor-alkali process. In this process, sodium chloride is electrolyzed in water to produce sodium hydroxide, chlorine gas, and hydrogen gas.

Step 2: The gases produced and their respective electrodes:
- At the anode (positive electrode), gas X is produced, which is chlorine gas (Cl₂). - At the cathode (negative electrode), gas Y is produced, which is hydrogen gas (H₂).

Step 3: Reaction between one of the gases and calcium hydroxide:
When chlorine gas (Cl₂) reacts with dry calcium hydroxide (Ca(OH)₂), it forms calcium hypochlorite (Ca(OCl)₂), which is widely used in water treatment plants and textile industries.

The chemical equation for the reaction is:
\[ \text{Cl}_2 + \text{Ca(OH)}_2 \rightarrow \text{Ca(OCl)}_2 + \text{H}_2\text{O} \]

Step 4: Conclusion:
- The process used to prepare sodium hydroxide from sodium chloride is the chlor-alkali process. - The gases produced are chlorine gas (Cl₂) at the anode and hydrogen gas (H₂) at the cathode. - The compound formed by the reaction of chlorine gas with dry calcium hydroxide is calcium hypochlorite (Ca(OCl)₂), used in water treatment and textile industries.