Sodium chloride molten, electrolysis

Electrolysis of Molten Sodium Chloride. Electrolysis of Water Electrolysis of an Aqueous Sodium Chloride Solution. Quantitative Aspects of Electrolysis... 

These facts would suggest that die electrolysis of molten alkali metal salts could lead to the inuoduction of mobile elecU ons which can diffuse rapidly through a melt, and any chemical reduction process resulting from a high chemical potential of the alkali metal could occur in the body of the melt, rather than being conhned to the cathode volume. This probably explains the failure of attempts to produce tire refractoty elements, such as titanium, by elecU olysis of a molten sodium chloride-titanium chloride melt, in which a metal dust is formed in the bulk of the elecU olyte. 

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... 

Molten sodium chloride decomposes into sodium and chlorine in this electrolytic cell. The sodium chloride is said to undergo electrolysis, or to be electrolyzed. 

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. 

Some metals are extracted in electrolytic cells. In section 11.3, you saw the extraction of sodium from molten sodium chloride in a Downs cell. Other reactive metals, including lithium, beryllium, magnesium, calcium, and radium, are also extracted industrially by the electrolysis of their molten chlorides. 

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. 

Sodium is produced by an electrolytic process, similar to the other alkali earth metals. (See figure 4.1). The difference is the electrolyte, which is molten sodium chloride (NaCl, common table salt). A high temperature is required to melt the salt, allowing the sodium cations to collect at the cathode as liquid metallic sodium, while the chlorine anions are liberated as chlorine gas at the anode 2NaCl (salt) + electrolysis —> Cl T (gas) + 2Na (sodium metal). The commercial electrolytic process is referred to as a Downs cell, and at temperatures over 800°C, the liquid sodium metal is drained off as it is produced at the cathode. After chlorine, sodium is the most abundant element found in solution in seawater. 

If a chemical reaction can make electricity it should not be surprising to learn that electricity can make a chemical reaction. Using an electric current to cause a chemical reaction is called electrolysis, a technique widely used to win elements from their compounds. For example, pure sodium metal (Na) and chlorine gas (CI2) are obtained by passing electricity through molten sodium chloride (NaCl). The study of the interplay of electricity and oxidation-reduction reactions is called electrochemistry. 

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. 

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 ... 

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... 

Reactive metals are usually difficult to extract. The preferred method is by electrolysis of the molten ore (electrolytic reduction) for example, sodium from 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... 

The only reasonably successful advance in this sense is the Alcoa process, based on the electrolysis of aluminium trichloride in a 2-15 per cent concentration at 700°C in a 3 2 mixture of molten sodium chloride and potassium chloride using carbon electrodes. Aluminium oxide is previously converted into aluminium chloride using chlorine from electrolysis. The reactions are thus... 

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. 

When molten sodium chloride is decomposed by electrolysis free chlorine is formed at the anode ... 

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. 

Electrolysis of molten NaCI Just as electrolysis can decompose water into its elements, it also can separate molten sodium chloride into sodium metal and chlorine gas. This process, the only practical way to obtain elemental sodium, is carried out in a chamber called a Down s cell, as shown in Figure 21-18. The electrolyte in the cell is the molten sodium chloride itself. Remember that ionic compounds can conduct electricity only when their ions are free to move, such as when they are dissolved in water or are in the molten state. 

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

---