Melting point of sodium chloride

FIGURE 12.15 In the Downs process, molten sodium chloride is electrolyzed with a graphite anode (at which the Cl ions are oxidized to chlorine) and a steel cathode (at which the Na4 ions are reduced to sodium). The sodium and chlorine are kept apart by the hoods surrounding the electrodes. Calcium chloride is present to lower the melting point of sodium chloride to an economical temperature. 

In a clean, dry crucible, mass out approximately 1 g of lithium chloride, LiCl, another typical ionic compound. (The melting point of sodium chloride, NaCl, is too high to observe using classroom laboratory equipment.)... 

Which of the following explains why the melting point of sodium chloride (NaCl 801 °C) is lower than the melting point of calcium fluoride (CaF2 1423°C) ... 

The large cell used for the electrolysis of sodium chloride in industry is known as a Downs cell. To decrease heating costs, calcium chloride is added to lower the melting point of sodium chloride from about 800°C to about 600°C. The reaction produces sodium and calcium by reduction at the cathode, and chlorine by oxidation at the anode. 

The melting point of sodium chloride is 800°C [301], At this high temperature, the chlorine gas obtained at the anode, would corrode all the cell components getting into contact with it. The sodium solubility in the molten salt is high (4.2 wt%) and so is its vapor pressure (50 kPa) [302], Therefore an electrolyte of lower melting point must be used. 

Sodium metal is produced by the electrolysis of molten rock salt (impure sodium chloride) and calcium chloride. Calcium chloride lowers the melting point of sodium chloride (recall freezing point depression), increasing the energy efficiency of the process. 

The common argument that only elements are pure substances and that sodium chloride contains sodium and chlorine should be rejected. This is because one measures constant values for the density or for the melting point of sodium chloride, and will find such constants of other compounds in well-known published tables. Having a defined density, melting and boiling point, the related substance is considered as a pure substance, e.g. water or ethanol. Pure substances are elements and compounds ... 

Metallic sodium is most conveniently obtained from molten sodium chloride by electrolysis in the Downs cell (see Section 19.8). The melting point of sodium chloride is rather high (801°C), and much energy is needed to keep large amounts of the substance molten. Adding a suitable substance, such as CaCl2, lowers the melting point to about 600°C—a more convenient temperature for the electrolysis process. 

Binding Atoms Together The properties of substances, such as the low conductivity and high melting point of sodium chloride crystals, depend on the properties of their atoms and how they bind together, as you ll see in this chapter. 

When metals and nonmetals react, the resulting ionic compounds are very stable large amounts of energy are required to "take them apart." For example, the melting point of sodium chloride is approximately 800 °C. 

From the point of view of the physical properties of sodium and sodium chloride there are three temperature areas within which reduction of titanium tetrachloride to metal appears possible (46) (1) below the melting point of sodium chloride—i.e., 800° C. (2) between this melting point and the boiling point of sodium or 880 C. and (3) above this boiling point but below the temperature at which titanium reacts with iron, which is about 975° C. 

Although crystals of table salt (sodium chloride) and table sugar (sucrose) look very similar to the naked eye, the melting point of sucrose (186 "C) is several hundred degrees less than the melting point of sodium chloride (801 C). Explain. 

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