The Electrolysis of Aqueous Sodium Chloride

Consider the electrolysis of a moderately concentrated solution of NaCl in water, using inert electrodes. The following experimental observations are made when a sufficiently high voltage is applied across the electrodes of a suitable cell. 

H2 gas is liberated at one electrode. The solution becomes basic in that vicinity. 

Chloride ions are obviously being oxidized to CI2 in this cell, as they were in the electrolysis of molten NaCl. But Na ions are not reduced to metallic Na. Instead, gaseous H2 and aqueous OH ions are produced by reduction of H2O molecules at the cathode. Water is more easily reduced than Na ions. This is primarily because the reduction of Na would produce the very active metal Na, whereas the reduction of H2O produces the more stable products H2(g) and OH (aq). The active metals Li, K, Ca, and Na (see Table 6-9) all react with water to produce H2(g) and the corresponding metal hydroxide [LiOH, KOH, Ca(OH)2, and NaOH], so we do not expect these metals to be produced in aqueous solution. Later in this chapter (Section 21-14), we learn the quantitative basis for predicting which of several possible oxidations or reductions is favored. The half-reactions and overall cell reaction for this electrolysis are 

2 NaOH + H2 + CI2 (overall cell reaction as formula unit equation) 

The overall cell reaction produces gaseous H2 and CI2 and an aqueous solution of NaOH, called caustic soda. Solid NaOH is then obtained by evaporation of the solution. This is the most important commercial preparation of each of these substances. It is much less expensive than the electrol)rsis of molten NaCl because it is not necessary to heat the solution to the high temperatures needed to melt NaCl. 

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The fluoride and chloride ions are very difficult to oxidize (Elx F = —2.889 V E°x Cl- = —1.360 V). Hence the elements fluorine and chlorine are ordinarily prepared by electrolytic oxidation, using a high voltage. As pointed out in Chapter 18, chlorine is prepared by the electrolysis of aqueous sodium chloride ... 

The electrolysis of aqueous sodium chloride is used to prepare chlorine, sodium, and hydrogen. 

When an aqueous salt solution is electrolyzed, the electrode reactions may differ from those for electrolysis of the molten salt because water may be involved. In the electrolysis of aqueous sodium chloride, for example, the cathode half-reaction might be either the reduction of Na+ to sodium metal, as in the case of molten sodium chloride, or the reduction of water to hydrogen gas ... 

The electrolysis of aqueous sodium chloride (brine) is an important industrial process for the production of chlorine and sodium hydroxide. In fact, this process is the second largest consumer of electricity in the United States, after the production of aluminum. Write a balanced equation for the electrolysis of aqueous sodium chloride (hydrogen gas is also produced). 

Chlorine (0.19% of lithosphere) is produced mainly from NaCl which is either crystallised from brines or mined. The gas is a product of the electrolysis of aqueous sodium chloride for caustic soda production, with carbon anodes and a mercury cathode. It is also a by-product of the manufacture mainly of metallic sodium, but also of magnesium and calcium, by electrolysing the appropriate fused chloride. Its chief uses are as a bleach, a bactericide, and an industrial chemical. 

Since ca. 97% of the chlorine is produced from the electrolysis of aqueous sodium chloride solution, the linked products sodium hydroxide and hydrogen are produced as byproducts ... 

Almost the whole production of chlorine is produced by the electrolysis of aqueous sodium chloride solutions. Only a small part is obtained by the electrolysis (or oxidation) of hydrochloric acid (or hydrogen chloride) (see Section 1.7.3). Small quantities of chlorine are also produced in the electrochemical manufacture of metals such as sodium. 

In this chapter, roughly one dozen quite different production processes will be summarized. For instance, the most important electrochemical process, the electrolysis of aqueous sodium chloride leading to chlorine, alkali, hydrogen, and chlorine oxygen compounds are incorporated (Sect. 5.2). Other processes are carried out in a small scale only, but have an unchallenged place in the technical chemistry, for instance, the generation of molecular fluorine (Sect. 5.3). Others are of limited importance nowadays, but may gain importance in the future, for example, the electrolysis of water (Sect. 5.4). 

A cell similar in principle to the diaphragm cell described above and operated without a diaphragm gives the same initial products but allows these to react with each other (Eqs. 8.24, 8.12-8.16). This is the basis of the chlorate cell. The initial electrochemical products ultimately form sodium chlorate as the final cell product from the electrolysis of aqueous sodium chloride [11]. Part of the product formation involves the chemical chlorate formation just outlined (Eqs. 8.12-8.16), and part of it forms from electrolytic chlorate formation (Eq. 8.28). 

Thus, the half-cell reactions in the electrolysis of aqueous sodium chloride are... 

The electrolysis of aqueous sodium chloride (brine) is an important industrial process for the production of chlorine and sodium hydroxide. In fact, this process is the... 

The electrolysis of aqueous sodium chloride, normally brine obtained directly from natural salt deposits, to yield chlorine, sodium hydroxide and hydrogen is the largest of the electrolytic industries. In the USA, the annual production of chlorine is of the order of 10 tons while in the UK it is about 1.7 x 10 tons. 

A (a) Metallic magnesium cannot be obtained by electrolysis of aqueous magnesium chloride, MgCb. Why (b) There are no sodium ions in the overall cell reaction for the electrolysis of aqueous sodium chloride. Why ... 

The electrolysis of aqueous sodium chloride is the basis of the chlor-alkali industry, the major commercial source of chlorine and sodium hydroxide. CommCTcial cells are of several types, but in each the main problem is to keep the products separate, because chlorine reacts with aqueous sodium hydroxide. 

The older chlor-alkali mercury cell is a cell for the electrolysis of aqueous sodium chloride in which mercury metal is used as the cathode (Figure 20.23). At the mercury cathode, sodium ion is reduced in preference to water. Sodium ion is reduced to sodium to form a liquid sodium—mercury alloy called sodium amalgam. (An amalgam is an alloy of mercury with any of various other metals.)... 

Sodium Compounds Sodium hydroxide, NaOH, is among the top ten industrial chemicals. It is produced by the electrolysis of aqueous sodium chloride. The overall electrolysis, which was described in Section 20.10, can be written as... 

Preparation and Uses of Chlorine Chlorine is a major industrial chemical. It is prepared commercially by the electrolysis of aqueous sodium chloride. Chlorine can be prepared in small amounts for laboratory use by the reaction of chloride ion with a strong oxidizing agent, such as potassium dichromate or manganese dioxide. However, chlorine is readily available in steel cylinders for laboratory work. 

Solutions of sodium hypochlorite are manufactured by allowing the chlorine gas released by the electrolysis of aqueous sodium chloride to mix with the cold solution of sodium hydroxide that is also obtained in the electrolysis. These solutions are sold... 

The Group VIIA elements, or halogens, are reactive. Chlorine (CI2), a pale greenish-yeUow gas, is prepared commercially hy the electrolysis of aqueous sodium chloride. Its principal uses are in the preparation of chlorinated hydrocarbons and as a bleaching agent and disinfectant. Hydrogen chloride, HCl, is one of the most important compounds of chlorine aqueous solutions of HCl are known as hydrochloric acid. 

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