When electricity is passed through an aqueous solution of sodium chloride. it decomposes to form sodium hydroxide this process is known as chlor alkali process
NaCl+2H2O ----- 2NaOH+Cl2+ H2

Chlor-alkali process: Explanation and Details

The chlor-alkali process is an industrial process that is used to produce chlorine gas, sodium hydroxide (caustic soda), and hydrogen gas (or hydrogen peroxide). This process involves the electrolysis of a solution of salt (sodium chloride) in water. The process is named after the two main products produced, which are chlorine (Cl) and alkali (NaOH).

The Process:
The chlor-alkali process involves the following steps:

1. Brine Preparation: A concentrated solution of salt (NaCl) is dissolved in water to form brine. This step is usually done by mining salt deposits or by evaporation of seawater.

2. Electrolysis: The brine solution is then passed through an electrolysis cell. An electric current is passed through the brine solution, which causes the sodium and chloride ions to dissociate. The positive sodium ions are attracted to the negative electrode (cathode), while the negative chloride ions are attracted to the positive electrode (anode). The following reactions occur at the electrodes:

Cathode: 2H2O + 2e- → H2 + 2OH-
Anode: 2Cl- → Cl2 + 2e-

The hydrogen gas is released at the cathode, while the chlorine gas is released at the anode. The hydroxide ions (OH-) combine with the sodium ions (Na+) to form sodium hydroxide (NaOH).

3. Product Separation: The chlorine gas, sodium hydroxide, and hydrogen gas are then separated from each other using various methods such as absorption, condensation, and compression.

Applications:
The products of the chlor-alkali process have various industrial applications:

1. Chlorine gas is used in the production of a wide range of chemicals, including PVC, solvents, and refrigerants.

2. Sodium hydroxide (caustic soda) is used in the production of pulp and paper, textiles, detergents, and soaps.

3. Hydrogen gas is used in the production of ammonia, methanol, and other chemicals.

Environmental Impact:
The chlor-alkali process has some environmental impacts, including the release of greenhouse gases (such as chlorine, hydrogen, and carbon dioxide) and the production of hazardous waste (such as mercury, which is used as a catalyst in some electrolysis cells). However, modern chlor-alkali plants have implemented various measures to minimize these impacts, such as the use of membrane technology instead of mercury cells and the recovery of byproducts for reuse.