Down’s cell

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... 

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. 

The anode reaction of the Down s cell is the oxidation of chloride ions. 

In a Down s cell, electrons supplied by a generator are used to reduce sodium ions. As electrons are removed from the anode, chloride ions are oxidized to chlorine gas. 

Occasionally, the market will swing the other way leaving chlorine in short supply. Fused sodium chloride is commercially electrolyzed in Down s cells to give chlorine and metallic sodium [11]. Sodium production in the U.S.A. has averaged 135,000-150,000 metric tonnes annually since 1968, which represents about a 2-3% contribution to the chlorine supply from this source. In the U.K., it is estimated that as much as 10% of the available chlorine arises from Down s cell technology. Potassium chloride solutions are also electrolyzed for commercial potassium hydroxide, but the contribution to the chlorine supply from this source is even less than from fused sodium chloride electrolysis. 

O Reading Check Explain why the sodium chloride must be molten in the Down s cell. 

Calculate Use Table 20.1 to calculate the voltage of the Down s cell. Should the potential be positive or negative ... 

Down s Cell What reaction takes place at the cathode when molten sodium chloride is electrolyzed ... 

The general technology may be illustrated by the example of sodium production in the Down s cell. The electrolyte is a molten mixture of sodium chloride (40%) and calcium chloride (60 wt %) requiring a process temperature of about 600°C. The principle of cell design is shown in Fig. 4.4, although more... 

Fig. 4A Down s cell for the extraction of sodium metal via electrolysis of molten NaCI or CaClj,...

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