Sodium chloride electrolysis of molten

This process is a major industrial somce of pure sodium metal and chlorine gas. 

Student Annotation We can only estimate the value of °ei because the values in Table 19.1 refer to the species in aqueous solution. 

Using data from Table 19.1, we estimate A eii to be 4 V for this process. The negative standard reduction potential indicates that for the process to occur as written, a minimum of approximately 4 V must be supplied by the battery to drive the reaction in the desired direction. In practice, an even higher voltage is required because of inefficiencies in the electrolytic process and because of overvoltage, a phenomenon we will discuss later in this section. 

Under ordinary atmospheric conditions (1 atm and 25°C), water will not spontaneously decompose to form hydrogen and oxygen gas because the standard fiee-eneigy change for the reaction is a large positive quantity  

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Sodium metal is obtained by the electrolysis of molten sodium chloride (Figure 20.3, p. 537). The electrode reactions are quite simple ... 

Write a balanced equation to represent the electrolysis of molten sodium chloride. What volume of Cl2 at STP is formed at the anode when... 

Sodium metal is produced from the electrolysis of molten sodium chloride in the Downs process (Section 12.13). Determine (a) the standard Gibbs free energy of the reaction... 

The electrolysis of molten sodium chloride is an important industrial reaction. Figure 11.15 shows the large electrolytic cell used in the industrial production of sodium and chlorine. You will meet other industrial electrolytic processes later in this chapter. 

O Most industrial reactions take place on a much larger scale than reactions in a laboratory or classroom. The voltage used in a Downs cell for the industrial electrolysis of molten sodium chloride is not very high, about 7 V to 8 V. However, the current used is 25 000 A to 40 000 A. Assuming a current of 3.0 x 10 A, determine the mass of sodium and the mass of chlorine made in 24 h in one Downs cell. Express your answers in kilograms. 

You have already seen that chlorine gas can be made by the electrolysis of molten sodium chloride. In industry, some chlorine is produced in this way using the Downs cell described earlier. However, more chlorine is produced in Canada using a different method, called the chlor-alkali process. In this process, brine is electrolyzed in a cell like the one shown in Figure 11.32. Brine is a saturated solution of sodium chloride. 

Electrolysis is used to decompose many compounds into their constituent elements. You have seen this process with water. Another example is the electrolysis of molten sodium chloride to yield molten sodium metal and chlorine gas ... 

The basic unit of electrical charge used by chemists is appropriately called a Faraday, which is defined as the charge on one mole of electrons (6 X 10 electrons). Incidentally, note that chemists have extended the original definition of the mole as a unit of mass to a corresponding number (Avogadro s number) of particles. Use the electrolysis of molten sodium chloride to see the relationship between Faradays of electricity and moles of decomposition products. 

The electrolysis of molten sodium chloride produces pure sodium metal (Na) and chlorine gas (CI2). How many Faradays of electricity are needed to produce 500 grams of CI2 The half-reaction forming CI2 is... 

An electrolytic cell has two electrodes that dip into an electrolyte and are connected to a battery or some other source of direct electric current. A cell for electrolysis of molten sodium chloride, for example, is illustrated in Figure 18.15. The battery serves as an electron pump, pushing electrons into one electrode and pulling them out of the other. The negative electrode attracts Na+ cations, which combine with the electrons supplied by the battery and are thereby reduced to liquid sodium metal. Similarly, the positive electrode attracts Cl- anions, which replenish the electrons removed by the battery and are thereby oxidized to chlorine gas. The electrode reactions and overall cell reaction are... 

FIGURE 18.15 Electrolysis of molten sodium chloride. Chloride ions are oxidized to Cl2 gas at the anode, and Na+ ions are reduced to sodium metal at the cathode. 

FIGURE 18.16 Cross- sectional view of a Downs cell for commercial production of sodium metal by electrolysis of molten sodium chloride. The cell design keeps the sodium and chlorine apart so that they can t react with each other. 

Sodium Rock salt Sodium chloride NaCI Electrolysis of molten sodium chloride... 

An electrolysis reaction in which the oxidation reaction is not the reverse of the reduction reaction is the electrolysis of molten sodium chloride. Molten sodium chloride (NaCl), with calcium chloride (CaCy added to decrease the melting point, is electrolyzed in a Downs cell, in which the sodium and chlorine products are separated so that sodium chloride does not reform. The following reactions occur ... 

What is the minimum voltage that must be applied to a Down s cell to cause the electrolysis of molten sodium chloride The net cell reaction is... 

Sodium metal is produced mainly by the electrolysis of molten sodium chloride. Because solid NaCl has a rather high melting point (800°C), it is usually mixed with solid CaCl2 to lower the melting point to about 600°C. The mixture is then electrolyzed in a Downs cell, as illustrated in Fig. 11.25, where the reactions are as follows ... 

The Downs cell for the electrolysis of molten sodium chloride. The cell is designed so that the sodium and chlorine produced cannot come into contact with each other to re-form NaCl. 

The Electrolysis of Molten Sodium Chloride. Molten sodium chloride (the salt melts at 801° C) conducts an electric current, as do other molten salts. During the process of conducting the current a chemical reaction occurs—the salt is decomposed. If two electrodes (carbon rods) are dipped into a crucible containing molten sodium chloride and an electric potential (from a battery or generator) is applied, metallic sodium is produced at the negative electrode—the cathode—and chlorine gas at the positive electrode—the anode. Such electrical decomposition of a substance is called electrolysis. 

Sodium is a light soft ductile metal of 0.97 specific gravity, which melts at 97.6 C. (208 F.) and boils at 760 C. (1382 ). It is obtaim d by the electrolysis of molten sodium chloride (common salt). On contact w ith water, sodium decomposes it with vigorous evolution of hydrogen. The heat of reaction is sufficient to ignite the hydrogen ami, heni c, in the presence of moisture, sodium is spontaneously inflammable. 

Sodium is such a reactive metal that preparing it through a chemical process can be dangerous. Sir Humphry Davy first isolated it in 1807 by the electrolysis of molten sodium hydroxide. Today, sodium is made by the electrolysis of molten sodium chloride in a Downs cell, as shown in Figure 17. 

Compare the reactions involved in the electrolysis of molten sodium chloride with those in the electrolysis of brine. 

Downs cell Electrolytic cell used for the commercial electrolysis of molten sodium chloride to produce commercial-grade sodium. 

A useful property of metallic mercury is that it forms amalgams with other metals, which have a host of uses. For example, metallic sodium is produced as an amalgam by electrolysis of molten sodium chloride. Dentists use a 50% amalgam with an alloy of silver for fillings. 

The Electrolysis of Molten Sodium Chloride fThe Downs Cell)... 

In Davy s electrolysis of molten NaCl, sodium ions were reduced to metallic sodium at the cathode. The oxidation of chloride ions to chlorine gas occurred at the second electrode, the anode. Each half-reaction in the electrolysis of molten sodium chloride is shown. 

A device called a Downs cell is used for the electrolysis of molten sodium chloride. As an electrical current is passed through the cell, liquid sodium forms at the circular iron cathode. Because liquid sodium is less dense than molten sodium chloride, the sodium floats to the surface and is collected. Chlorine gas forms at the carbon anode and is collected at the top. An iron screen separates the two electrodes. 

How is electrolysis of a sodium chloride solution different from electrolysis of molten sodium chloride In molten NaCl, the only ions present are Na+ and CU. What ions are present in an aqueous solution of rock salt Recall that water dissociates slightly to form H+ and OH ions. 

Chlorine gas is used in the production of many other chemicals, including carbon tetrachloride, polyvinyl chloride plastic, and hydrochloric acid, ft is produced ftom the electrolysis of molten sodium chloride. What minimum mass of sodium chloride in megagrams is necessary to make 2.7 X 10 L of chlorine gas at standard temperature and pressure, STP ... 

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