Calcium chloride melting point

In general, the electrolysis of a molten salt at inert electrodes produces the metal at the cathode, e.g., calcium from calcium chloride (melting point 774 °C). The anion is often a halide ion which, on discharge, yields the halogen, e.g., chlorine from calcium chloride. 

The ammonia gas is used again and the only by-product, calcium chloride, is used to melt snow, prevent freezing of coal in transit and as an antidust treatment since it is hygroscopic and forms a solution of low freezing point. 

The metal has a silvery color, is rather hard, and is prepared by electrolysis of the fused chloride to which calcium fluoride is added to lower the melting point. 

The cell bath in early Downs cells (8,14) consisted of approximately 58 wt % calcium chloride and 42 wt % sodium chloride. This composition is a compromise between melting point and sodium content. Additional calcium chloride would further lower the melting point at the expense of depletion of sodium in the electrolysis 2one, with the resulting compHcations. With the above composition, the cells operate at 580—600°C, well below the temperature of highest sodium solubiUty in the salt bath. Calcium chloride causes problems because of the following equiUbrium reaction (56) ... 

Strontium chloride [10476-85-4] SrCl2, is similar to calcium chloride but is less soluble in water (100.8 g in 100 mL water at 100°C). The anhydrous salt forms colorless cubic crystals with a specific gravity of 3.052 and a melting point of 873°C. Strontium chloride is used in toothpaste formulations (see... 

Calcium metal was produced in 1855 by electrolysis of a mixture of calcium, strontium, and ammonium chlorides, but the product was highly contaminated with chlorides (1). By 1904 fairly large quantities of calcium were obtained by the electrolysis of molten calcium chloride held at a temperature above the melting point of the salt but below the melting point of calcium metal. An iron cathode just touched the surface of the bath and was raised slowly as the relatively chloride-free calcium solidified on the end. This process became the basis for commercial production of calcium metal until World War II. 

Usually a small amount of material remains undissolved. This material does not affect the melting point significantly but can be removed if desired by forcing the solution, kept hot by an electric heating mantle, through the filter arrangement described above into a dry flask protected from moisture by a calcium chloride tube. 

In order to open the flask, air is admitted slowly through a calcium chloride tube. The melting point of the anhydride drops somewhat during prolonged storage with occasional opening, but the purity does not seem to be affected appreciably. ... 

The charges of the ions. The bond in CaO (+2, —2 ions) is considerably stronger than that in NaCl (+1,-1 ions). This explains why the melting point of calcium oxide (2927°C) is so much higher than that of sodium chloride (801°C). 

The freezing points of electrolyte solutions, like their vapor pressures, are lower than those of nonelectrolytes at the same concentration. Sodium chloride and calcium chloride are used to lower the melting point of ice on highways their aqueous solutions can have freezing points as low as —21 and — 55°C, respectively. 

The cell is operated at about 600°C to keep the electrolyte molten calcium chloride is added to lower the melting point. About 14 kj of electrical energy is required to produce one gram of sodium, which is drawn off as a liquid (mp of Na = 98°C). The chlorine gas produced at the anode is a valuable byproduct. 

Calcium chloride (CaCI2) is added to lower the melting point. The iron screen prevents sodium and chlorine from coming into contact with each other. 

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. 

Fluorides are nonhygroscopic, and their melting points are higher than those of the corresponding chlorides. Besides, the fluoride reduction reactions are considerably more exothermic. The prime examples of the use of fluorides as intermediates are the reduction of uranium tetrafluoride by calcium or magnesium the reduction of rare earth fluorides by calcium, reduction of beryllium fluoride by magnesium and the reduction of potassium tantalum double fluoride by sodium. 

The electrolyte is made by in situ chlorination of vanadium to vanadium dichloride in a molten salt bath. Higher valent chlorides are difficult to retain in the bath and thus are not preferred. The molten bath, which is formed by sodium chloride or an equimolar mixture of potassium chloride-sodium chloride or of potassium chloride-lithium chloride or of sodium chloride-calcium chloride, is contained in a graphite crucible. The crucible also serves as an anode. Electrolysis is conducted at a temperature about 50 °C above the melting point of the salt bath, using an iron or a molybdenum cathode and a cathode current density of 25 to 75 A dnT2. The overall electrochemical deposition reaction involves the formation and the discharge of the divalent ionic species, V2+ ... 

Experiment.—Qninol from Quinone. Suspend about 2 g. of quinone in 50 c.c. of water and while shaking frequently saturate the suspension with sulphur dioxide. Keep for some time and then extract the now colourless liquid twice with ether, dry the ethereal extract with calcium chloride, and evaporate the ether. The residue of quinol crystallises. Recrystallise it from a little water. Melting point 169°. Warm a sample with dilute sulphuric acid and a few drops of dichromate solution the odour of quinone is emitted. 

The nitrosophenol is precipitated from the cooled aqueous solution by acidification with dilute sulphuric acid and is extracted with ether in a separating funnel. After brief drying over calcium chloride the brownish-green solution is concentrated on the water bath. The sparingly soluble compound crystallises from the ether on cooling. Melting point 120°-130° (decomp.). Complete purification of nitrosophenol is difficult. 

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. 

Fused sodium chloride is electrolyzed at hath temperature varying between 565 to 600°C at a cell voltage of 5.7 to 7 V and the cell current varying from 25 to 35 kA. The cathode current density is mostly about 9.8 kA/m. Often calcium chloride is added to sodium chloride in the cell bath to lower its melting point. Calcium is largely removed from sodium by filtration at about 110°C. Other electrolyte compositions have heen used in which calcium is partially or fully replaced. The cell feed must he free of sulfate and other impurities. 

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