The element chlorine is obtained for commercial use by which method?

Question

a. Isolation from gas pockets int he earth's crust
b. separation from air by a high pressure technique
c. filtration of brine (NaCl) solutions
d. electrolysis of aqueous NaCl solutions
e. mixing sulfur and argon in equal quantities

Answer 1

Chlorine can be manufactured by electrolysis of a sodium chloride solution (brine). There are three industrial methods for the extraction of chlorine by electrolysis.

Mercury cell electrolysis
Mercury cell electrolysis was the first method used to produce chlorine on an industrial scale. Titanium anodes are located above a liquid mercury cathode and a solution of sodium chloride is positioned between the electrodes. When an electrical current is applied, chloride is released at the titanium anodes and sodium dissolves into the mercury cathode forming an amalgam.

The amalgam can be regenerated into mercury by reacting it with water, producing hydrogen and sodium hydroxide. These are useful byproducts.

This method consumes vast amounts of energy and there are also concerns about mercury emissions.

Diaphragm cell electrolysis
An asbestos diaphragm is deposited on an iron grid cathode preventing the chlorine forming at the anode and the sodium hydroxide forming at the cathode from re-mixing.

This method uses less energy than the mercury cell, but the sodium hydroxide is not as easily concentrated and precipitated into a useful substance.

Membrane cell electrolysis
The electrolysis cell is divided into two by a membrane acting as an ion exchanger. Saturated sodium chloride solution is passed through the anode compartment leaving a lower concentration. Sodium hydroxide solution is circulated through the cathode compartment exiting at a higher concentration. A portion of this concentrated sodium hydroxide solution is diverted as product while the remainder is diluted with deionized water and passed through the electrolyzer again.

This method is nearly as efficient as the diaphragm cell and produces very pure sodium hydroxide but requires very pure sodium chloride solution..

Cathode: 2 H+(aq) + 2e– ---> H2(g)
Anode: 2Cl– ---> Cl2 (g) + 2e–
Overall equation: 2NaCl + 2H20 ---> Cl2 + H2 + 2 NaOH

Before electrolytic methods were used for chlorine production, the direct oxidation of hydrogen chloride with oxygen or air was exercised in the Deacon process:

4HCl + O2 → 2Cl2 + 2H2O
This reaction was accomplished with the use of CuCl2 as a catalyst. Due to the extremely corrosive reaction mixture, industrial use of this method is difficult.

Another earlier process to produce chlorine is to heat brine with acid and manganese dioxide.

2NaCl + 2H2SO4 + MnO2 → Na2SO4 + MnSO4 + 2H2O + Cl2
Using this process, chemist Carl Wilhelm Scheele was the first to isolate chlorine in a laboratory. The manganese can be recovered by the Weldon process.

In a laboratory, small amounts of chlorine gas can be created by adding concentrated hydrochloric acid (typically about 5M) to sodium chlorate solution.

Answer 2

Mercury cell electrolysis
Mercury cell electrolysis was the first method used to produce chlorine on an industrial scale. Titanium anodes are located above a liquid mercury cathode and a solution of sodium chloride is positioned between the electrodes. When an electrical current is applied, chloride is released at the titanium anodes and sodium dissolves into the mercury cathode forming an amalgam.

The amalgam can be regenerated into mercury by reacting it with water, producing hydrogen and sodium hydroxide. These are useful byproducts.

This method consumes vast amounts of energy and there are also concerns about mercury emissions.

[edit]
Diaphragm cell electrolysis
An asbestos diaphragm is deposited on an iron grid cathode preventing the chlorine forming at the anode and the sodium hydroxide forming at the cathode from re-mixing.

This method uses less energy than the mercury cell, but the sodium hydroxide is not as easily concentrated and precipitated into a useful substance.

[edit]
Membrane cell electrolysis
The electrolysis cell is divided into two by a membrane acting as an ion exchanger. Saturated sodium chloride solution is passed through the anode compartment leaving a lower concentration. Sodium hydroxide solution is circulated through the cathode compartment exiting at a higher concentration. A portion of this concentrated sodium hydroxide solution is diverted as product while the remainder is diluted with deionized water and passed through the electrolyzer again.

This method is nearly as efficient as the diaphragm cell and produces very pure sodium hydroxide but requires very pure sodium chloride solution..

Cathode: 2 H+(aq) + 2e– ---> H2(g)
Anode: 2Cl– ---> Cl2 (g) + 2e–
Overall equation: 2NaCl + 2H20 ---> Cl2 + H2 + 2 NaOH

[edit]
Other methods
Before electrolytic methods were used for chlorine production, the direct oxidation of hydrogen chloride with oxygen or air was exercised in the Deacon process:

4HCl + O2 → 2Cl2 + 2H2O
This reaction was accomplished with the use of CuCl2 as a catalyst. Due to the extremely corrosive reaction mixture, industrial use of this method is difficult.

Another earlier process to produce chlorine is to heat brine with acid and manganese dioxide.

2NaCl + 2H2SO4 + MnO2 → Na2SO4 + MnSO4 + 2H2O + Cl2
Using this process, chemist Carl Wilhelm Scheele was the first to isolate chlorine in a laboratory. The manganese can be recovered by the Weldon process.

In a laboratory, small amounts of chlorine gas can be created by adding concentrated hydrochloric acid (typically about 5M) to sodium chlorate solution.

Answer 3

Chlorine is produced commercially chiefly by the electrolysis of sodium chloride, either molten or in solution. Other chlorides are sometimes employed. Chlorine can also be prepared from hydrochloric acid by oxidation of the hydrogen chloride (Deacon's process) and from bleaching powder.

Answer 4

d) Electrolysis of aqueous NaCl solutions.