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: Sodium Hydroxide Production from Sodium Chloride:
The chlor-alkali process is employed to synthesize sodium hydroxide (NaOH) from sodium chloride (NaCl). This electrochemical method involves the electrolysis of sodium chloride in water, yielding sodium hydroxide, chlorine gas, and hydrogen gas.

Step 2: Identification of Gases and Electrodes:
- Gas X, identified as chlorine gas (Cl₂), is generated at the anode (positive electrode).
- Gas Y, identified as hydrogen gas (H₂), is generated at the cathode (negative electrode).

Step 3: Reaction of Chlorine Gas with Calcium Hydroxide:
The reaction between chlorine gas (Cl₂) and anhydrous calcium hydroxide (Ca(OH)₂) produces calcium hypochlorite (Ca(OCl)₂). This compound finds extensive application in water purification and the textile industry.

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

Step 4: Summary:
- Sodium hydroxide is manufactured from sodium chloride via the chlor-alkali process.
- Chlorine gas (Cl₂) is produced at the anode, and hydrogen gas (H₂) is produced at the cathode.
- The reaction of chlorine gas with dry calcium hydroxide yields calcium hypochlorite (Ca(OCl)₂), utilized in water treatment and textile applications.