Alkali metal melts

The alkali metals melt at low temperatures. They are the most reactive metals. 

TABLE 6.4 Properties of Alkali Metals Melting Boiling Point (°C) Point (°C) Density (g/cm3) First Ionization Energy (kj/mol) Abundance on Earth (%) Atomic Radius (pm) Ionic (M+) Radius (pm)... 

Table Properties of alkali metals melting and boiling points, atomisation and ionisation enthalpies, ionic and standard electrode potentials...

Reactions of carboxylates containing the more electropositive cations yield product carbonates, or sometimes the basic carbonates. Some of these salts, e.g., those of the alkali metals, melt before decomposition. The oxide products from decomposition of the lanthanide compounds may contain carbon deposited as a result of carbon monoxide disproportionation. Kinetic measurements must include due consideration of the possible retention of carbon dioxide by the product (as COj ) and the secondary reactions involved in carbon deposition. 

The dflialides, like the trihalides, undergo disporportionation, in this case yielding the metal and the tetrahalide. There seems to be some uncertainty in the temperature at which this reaction becomes significant. For instance, the dichloride of zirconium is reported to be unstable in alkali and alkali metal melts at 400°C, on the one hand (490) and stable in a 50 50 sodium chloride-potassium chloride eutectic at 750°C, on the other (550). The stability does seem to be somewhat dependent on the... 

Single crystals (M = La, Ce, Pr, Nd, and Sm) were obtained by the iodine transport reaction method [10] or by spontaneous crystallization from ACl (A = alkali metal) melts [12]. 

Sulphonic acids. The aromatic sulphonic acids and their alkali metal salts are soluble in water, but insoluble in ether (Solubility Group II). They are best characterised by conversion into crystalline S-benzyl-iso-thiuronium salts (see Section IV,33,2 and 111,85,5), which possess characteristic melting points. A more time-consuming procedure is to treat the well-dried acid or... 

Metals do not generally react with vitreous siUca below 1000°C or their melting point, whichever is lower. Exceptions are alurninum, magnesium, and alkah metals. Aluminum readily reduces siUca at 700—800°C. Alkali metal vapors attack at temperatures as low as 200°C. Sodium vapor attack involves a diffusion of sodium into the glass, followed by a reduction of the siUca. 

Sodium [7440-23-5] Na, an alkali metal, is the second element of Group 1 (lA) of the Periodic Table, atomic wt 22.9898. The chemical symbol is derived from the Latin natrium. Commercial iaterest ia the metal derives from its high chemical reactivity, low melting poiat, high boiling poiat, good thermal and electrical conductivity, and high value ia use. 

A signiflcairt property of the alkali metal halides is the solubility of the metals in their molten halides. Typical values of the consolute temperatures of metal-chloride melts are 1180°C in Na-NaF, 1080°C in Na-NaCl, 790°C... 

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. 

A complication of tire extension of tire electrolysis route for metal production, is tlrat in the case of the alkali metals, there is a significant solubility of the metal which would be produced by electrolysis in tire molten chloride. The dissolved metal provides very mobile electrons to tire melt, thus reducing the salt resistance, and dissipating the increased cuiTent, at a given applied potential, without the production of metal. To describe this phenomenon in... 

Group IIA metals inelude Be, Mg, Ca, Sr, Ba and Ra whieh are grey, moderately-hard, high melting-point substanees. Like the alkali metals they attaek water to liberate hydrogen but with less vigour. The salts of the alkaline earths are generally less stable towards heat and water than those of alkali metals, and less water soluble. 

The chemical resistance of PTFE is almost universal It resists attack by aqua regia, hot fummg nitnc acid, hot caustic, chlorine, chlorosulfonic acid, and all solvents. Despite this broad chemical resistance, PTFE is attacked by molten alkali metals, ammonia solutions of such metals, chlorine trifluoride, and gaseous fluonne at elevated temperature and pressure PTFE swells or dissolves m certam highly fluonnated oils near its melting point. Specific lists of chemicals compatible with PTFE are available [/.8]... 

The Group 1 elements are soft, low-melting metals which crystallize with bee lattices. All are silvery-white except caesium which is golden yellow "- in fact, caesium is one of only three metallic elements which are intensely coloured, the other two being copper and gold (see also pp. 112, 1177, 1232). Lithium is harder than sodium but softer than lead. Atomic properties are summarized in Table 4.1 and general physical properties are in Table 4.2. Further physical properties of the alkali metals, together with a review of the chemical properties and industrial applications of the metals in the molten state are in ref. 11. 

The alkali metal halides are all high-melting, colourless crystalline solids which can be conveniently prepared by reaction of the appropriate hydroxide (MOH) or carbonate (M2CO3) with aqueous hydrohalic acid (HX), followed by recryslallization. Vast quantities of NaCl and KCl are available in nature and can be purihed if necessary by simple crystallization. The hydrides have already been discussed (p. 65). 

Figure 4.3 Melting point and boiling point of alkali metal halides.

Alkali metal nitrates are low-melting salts that decompose with evolution of oxygen above about 500 C, e.g. 

Deprotonation of H2O2 yields OOH , and hydroperoxides of the alkali metals are known in solution. Liquid ammonia can also effect deprotonation and NH4OOH is a white solid, mp 25° infrared spectroscopy shows the presence of NH4+ and OOH ions in the solid phase but the melt appears to contain only the H-bonded species NH3 and H202. " Double deprotonation yields the peroxide ion 02 , and this is a standard route to transition metal peroxides. 

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