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Chapter 22: Problem 51

(a) What are the three commercial products formed in the chlor-alkali process? (b) State an advantage and a disadvantage of using the mercurycell method for this process.

Short Answer

Expert verified
The three commercial products are Cl₂, H₂, and NaOH. An advantage is high purity NaOH, and a disadvantage is mercury pollution.

Step by step solution

01

Understanding the Chlor-Alkali Process

Identify the key products formed during the chlor-alkali process. This process involves the electrolysis of sodium chloride (NaCl) solution, also known as brine.
02

Identifying the Products

List the three main products formed: chlorine gas (Cl₂), hydrogen gas (H₂), and sodium hydroxide (NaOH). These are the commercial products obtained from the chlor-alkali process.
03

Advantage of the Mercury Cell Method

One advantage of the mercury cell method is that it produces very pure sodium hydroxide (NaOH) without contamination from chloride ions.
04

Disadvantage of the Mercury Cell Method

A major disadvantage of the mercury cell method is environmental pollution due to the release of mercury, which is toxic and harmful to both the environment and human health.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Commercial Products
The chlor-alkali process is a crucial industrial method. It produces three key commercial products through the electrolysis of sodium chloride solution (brine). These products are chlorine gas (Cl₂), hydrogen gas (H₂), and sodium hydroxide (NaOH). Because these substances are in high demand in various industries, the chlor-alkali process is extensively used worldwide. Chlorine gas has applications in water treatment and the production of plastics. Hydrogen gas is utilized in fuel and fertilizer production, while sodium hydroxide is used in the manufacture of paper, textiles, and soap.
Electrolysis of Sodium Chloride
Electrolysis is a chemical process that uses electric current to drive a non-spontaneous reaction. In the chlor-alkali process, an electric current is passed through a solution of sodium chloride (NaCl), known as brine.
This solution is typically placed in a specialized cell that facilitates the reaction.
The electrolysis of sodium chloride occurs as follows: at the anode (positive electrode), chloride ions (Cl⁻) are oxidized to chlorine gas (Cl₂). At the cathode (negative electrode), water is reduced to hydrogen gas (H₂) and hydroxide ions (OH⁻). The hydroxide ions combine with sodium ions (Na⁺) present in the solution to form sodium hydroxide (NaOH).
Chlorine Gas Production
Chlorine gas (Cl₂) production happens at the anode during the electrolysis of brine. When electric current is applied, chloride ions (Cl⁻) from the sodium chloride solution are attracted to the anode. Here, they lose electrons (oxidation) to form chlorine gas.
This chlorine gas is then collected and can be utilized for various purposes, including:
  • Disinfection and water treatment
  • Production of PVC and other plastics
  • Manufacturing of solvents and cleaning agents
Chlorine gas is highly reactive and must be handled with care due to its toxic properties.
Hydrogen Gas Production
Hydrogen gas (H₂) is produced at the cathode during the electrolysis of sodium chloride solution. The reaction involves the reduction of water molecules (H₂O), which split into hydrogen gas and hydroxide ions (OH⁻).
Hydrogen gas has several important applications, such as:
  • Fuel in hydrogen fuel cells
  • Production of ammonia for fertilizers
  • Refining of petroleum
The production of hydrogen gas in the chlor-alkali process makes this method not only useful for producing valuable chemicals but also contributes to the hydrogen economy.
Sodium Hydroxide Production
Sodium hydroxide (NaOH) is the third vital product of the chlor-alkali process. It forms when hydroxide ions (OH⁻) produced at the cathode combine with sodium ions (Na⁺) in the solution. Sodium hydroxide is an essential chemical used extensively in various industries.
Some of its applications include:
  • Paper and pulp manufacturing
  • Textile processing
  • Soap and detergent production
  • Petroleum refining
Its production via the chlor-alkali process ensures a steady and efficient supply to meet industrial demands.
Mercury Cell Method
The mercury cell method is one technology used in the chlor-alkali process. It uses mercury as the cathode, where it forms an amalgam with sodium. This amalgam reacts with water to produce pure sodium hydroxide (NaOH), hydrogen gas, and mercury which is reused.
The mercury cell method has the advantage of producing very pure sodium hydroxide without contamination from chloride ions. However, its primary disadvantage is significant environmental risks. The use of mercury poses threats due to its toxicity, leading to severe environmental pollution and health hazards when released into the environment.
Environmental Pollution
Environmental pollution is a critical concern in the chlor-alkali process, especially with the mercury cell method. Mercury is highly toxic and can pollute water bodies, harming aquatic life and entering the human food chain.
The release of chlorine gas also poses risks. Although it's useful in various applications, its highly reactive nature can cause respiratory problems and other health issues if not handled properly.
Efforts are ongoing to develop and implement greener and safer alternatives, such as the membrane cell method, which does not use mercury and poses fewer environmental risks.

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Most popular questions from this chapter

Several transition metals are prepared by reduction of the metal halide with magnesium. Titanium is prepared by the Kroll method, in which the ore (ilmenite) is converted to the gaseous chloride, which is then reduced to Ti metal by molten \(\mathrm{Mg}\) (see the discussion on the isolation of magnesium in Section 22.4 ). Assuming yiclds of \(84 \%\) for step 1 and \(93 \%\) for step \(2,\) and an excess of the other reactants, what mass of Ti metal can be prepared from 21.5 metric tons of ilmenite?

The final step in the smelting of CuFeS \(_{2}\) is $$ \mathrm{Cu}_{2} \mathrm{~S}(s)+2 \mathrm{Cu}_{2} \mathrm{O}(s) \longrightarrow 6 \mathrm{Cu}(I)+\mathrm{SO}_{2}(g) $$ (a) Give the oxidation states of copper in \(\mathrm{Cu}_{2} \mathrm{~S}, \mathrm{Cu}_{2} \mathrm{O},\) and \(\mathrm{Cu} .\) (b) What are the oxidizing and reducing agents in this reaction?

Phosphorus is one of the impurities present in pig iron that is removed in the basic-oxygen process. Assuming that phosphorus is present as \(\mathrm{P}\) atoms, write equations for its oxidation and subsequent reaction in the basic slag.

Elemental \(\mathrm{Li}\) and \(\mathrm{Na}\) are prepared by electrolysis of a molten salt, whereas \(\mathrm{K}, \mathrm{Rb},\) and \(\mathrm{Cs}\) are prepared by chemical reduction. (a) In general terms, explain why the alkali metals cannot be prepared by electrolysis of their aqueous salt solutions. (b) Use ionization energies (see the Family Portraits for Group \(1 \mathrm{~A}(1)\) in Section 14.3 and for Group \(2 \mathrm{~A}(2)\) in \(\operatorname{Section} 14.4)\) to explain why calcium should not be able to isolate \(\mathrm{Rb}\) from molten \(\operatorname{Rb} \mathrm{X}(\mathrm{X}=\) halide \()\) (c) Use physical properties to explain why calcium is used to isolate Rb from molten \(\mathrm{RbX}\). (d) Can Ca be used to isolate Cs from molten CsX? Explain.

Earth's mass is estimated to be \(5.98 \times 10^{24} \mathrm{~kg}\), and titanium represents \(0.05 \%\) by mass of this total. (a) How many moles of Ti are present? (b) If half of the Ti is found as ilmenite (FeTiO \(_{3}\) ), what mass of ilmenite is present? (c) If the airline and auto industries use \(1.00 \times 10^{5}\) tons of Ti per year, how many years will it take to use up all the Ti ( 1 ton \(=2000\) lb)?
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