Sodium chloride, sublimation

Mercuric chloride (bichloride of mercury), HgCl is a white crys talline substance invially made by dissolving mercury in hot concen trated sulfuric and, and then heating the dry mercuric sulfate with sodium chloride, subliming the volatile mercuric chloride ... 

Figure 1. Sodium chloride sublimation rate (mmole/hr.)...

S = Heat of sublimation of sodium D = Dissociation energy of chlorine / = Ionization energy of sodium = Electron affinity of chlorine Uq = Lattice energy of sodium chloride AHf = Heat of formation of sodium chloride. 

Mercuryill) chloride is obtained in solution by dissolving mercury(II) oxide in hydrochloric acid the white solid is obtained as a sublimate by heating mercury(II) sulphate and solid sodium chloride ... 

The oxime is freely soluble in water and in most organic liquids. Recrystallise the crude dry product from a minimum of 60-80 petrol or (less suitably) cyclohexane for this purpose first determine approximately, by means of a small-scale test-tube experiment, the minimum proportion of the hot solvent required to dissolve the oxime from about 0-5 g. of the crude material. Then place the bulk of the crude product in a small (100 ml.) round-bottomed or conical flask fitted with a reflux water-condenser, add the required amount of the solvent and boil the mixture on a water-bath. Then turn out the gas, and quickly filter the hot mixture through a fluted filter-paper into a conical flask the sodium chloride remains on the filter, whilst the filtrate on cooling in ice-water deposits the acetoxime as colourless crystals. These, when filtered anddried (either by pressing between drying-paper or by placing in an atmospheric desiccator) have m.p. 60 . Acetoxime sublimes rather readily when exposed to the air, and rapidly when warmed or when placed in a vacuum. Hence the necessity for an atmospheric desiccator for drying purposes. 

Because phenols are weak acids, they can be freed from neutral impurities by dissolution in aqueous N sodium hydroxide and extraction with a solvent such as diethyl ether, or by steam distillation to remove the non-acidic material. The phenol is recovered by acidification of the aqueous phase with 2N sulfuric acid, and either extracted with ether or steam distilled. In the second case the phenol is extracted from the steam distillate after saturating it with sodium chloride (salting out). A solvent is necessary when large quantities of liquid phenols are purified. The phenol is fractionated by distillation under reduced pressure, preferably in an atmosphere of nitrogen to minimise oxidation. Solid phenols can be crystallised from toluene, petroleum ether or a mixture of these solvents, and can be sublimed under vacuum. Purification can also be effected by fractional crystallisation or zone refining. For further purification of phenols via their acetyl or benzoyl derivatives (vide supra). 

In the ion-exchange method, brine solution is passed through an anion-exchange resin. Iodide (and polyiodide) anions from the solution adsorb onto the resin from which they are desorbed by treatment with caustic soda solution. The resin is treated with sodium chloride solution to regenerate its activity for reuse. The iodide solution (also rich in iodate, IO3 ions) is acidified with sulfuric acid. The acid solution is oxidized to precipitate out iodine. Iodine is purified by sublimation. 

The b.p. indicated above are by L. H. Borgstrom W. R. Mott gave 1300° and 1200° respectively for the b.p. of potassium and sodium chlorides. Lithium, sodium, and potassium chlorides begin to sublime at their m.p.,15 and probably alto the other salts as well. 

In 1705, L. Lemery 1 first showed that ammonium chloride exists among the products derived from volcanoes, where he found it admixed with sodium chloride, and this fact was verified by F. Seras in 1737, and by F. de Bonderoy in 1765. Ammonium chloride occurs as a sublimate mixed with other volatile matters in cavities VOL. ii. 2 o... 

Ammonium chloride is also formed by the action of hydrochloric acid on a soln. of ammonia or ammonium carbonate J. G. Qentele 5 made it by the double decomposition of ammonium bicarbonate and sodium, magnesium, calcium, and other chlorides H. J. E. Hennebutte and E. Mesnard, and A. Dubose and M. Heuzey, made it by the action of ammonium bicarbonate or sulphate on the double chloride of iron and calcium and it is made by the action of soln. of ammonium sulphate and sodium chloride when the soln. is cone, the crystals of sodium sulphate separate out and they are removed by suitable shovels the cone. soln. of ammonium chloride which remains is purified by crystallization. Ammonium chloride can also be obtained by sublimation from a dry intimate mixture of the same two salts. A. French made it by the joint action of air and steam on a mixture of salt, pyrites, and carbon or organic matter 2NaCl+4H20-j-S02+C-j-N2=2NH4Cl-i-Na2S04-i-C02. 

According to B. Schindler,16 potassium iodide volatilizes in free air when heated to the softening temp, of hard glass, and, according to B. Bunsen, and T. H. Norton and D. M. Both, it volatilizes from 0-352 to 0-423 times as fast as the same quantity of sodium chloride when heated in the hottest part of a Bunsen s flame. According to J. Dewar and A. Scott,17 the vapour density of potassium iodide is 169 8. A. von Weinberg obtained 43"3 Cals, for the heat of sublimation of sodium iodide, and 44 9 Cals, for that of potassium iodide and A. Beis obtained for sodium and potassium iodides respectively 51 and 46 Cals., and between 15 and 35 Cals, for lithium iodide. 

Disodium and barium hexafluorosilicate can also be used as fluorinating agents. High purity disodium hexafluorosilicate can be obtained from high purity diammonium hexafluorosilicate and sodium chloride. Diammonium hexafluorosilicate for this process is purified by sublimation.14... 

Halides of metals tend to be ionic unless the metal has an oxidation number greater than +2. For example, sodium chloride and copper(II) chloride are ionic compounds and have high melting points, but TiCl4 and FeCl3 sublime as molecules. 

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