Solutions of metals in ammonia

Solutions of metals in ammonia. One of the striking differences between water and ammonia is the behavior of alkali metals toward these solvents. With water, these metals react rapidly to liberate hydrogen ... 

As might be expected for solutions containing free electrons, solutions of metals in ammonia are not stable over long time periods, and hydrogen is slowly liberated ... 

Solutions of metals in ammonia combine the properties of metals and liquids. Structures of pure ammonia and solutions of lithium in it were studied repeatedly NHs molecules in a pure liquid have N 12 and rf(N- N) = 3.48 A, iV (H) = 7.5... 

Iron, cobalt, and nickel catalyze this reaction. The rate depends on temperature and sodium concentration. At —33.5°C, 0.251 kg sodium is soluble in 1 kg ammonia. Concentrated solutions of sodium in ammonia separate into two Hquid phases when cooled below the consolute temperature of —41.6°C. The compositions of the phases depend on the temperature. At the peak of the conjugate solutions curve, the composition is 4.15 atom % sodium. The density decreases with increasing concentration of sodium. Thus, in the two-phase region the dilute bottom phase, low in sodium concentration, has a deep-blue color the light top phase, high in sodium concentration, has a metallic bronze appearance (9—13). 

Reactions of inorganic substances with solutions of metals in liquid ammonia. G. W. Watt, Chem. Rev., 1950, 46,289-315 (165). 

Solutions of metals in liquid ammonia conduct electricity better than any salt in any liquid and the main current carrier is the solvated electron. This implies that the electron gets free from the parent metal atom sodium and occupy cavities in the liquid. At higher alkali metal concentrations the solutions are copper coloured and have a metallic lustre and all electrical conductivity studies indicate that they are very similar to liquid metals. 

Sodium is quite soluble in liquid ammonia, forming a saturated solution which contains 5.7 molecules of ammonia per atom of sodium. The density of the saturated solution is 0.578 g./cc. at —33.8°C. the specific conductance is 5047, and the atomic conductance is 0.800 X 104. Considerable expansion occurs when a metal is dissolved in ammonia, and it may be pointed out that a saturated solution of lithium in ammonia is the lightest liquid known at room temperature, having a density of only 0.477 g./cc. 

The two mass action equilibria previously indicated have been used in conjunction with a modified form of the Shedlovsky conductance function to analyze the data in each of the cases listed in Table I. Where the data were precise enough, both K2 and K were calculated. As mentioned previously, the K s so evaluated are practically the same as those obtained for ion pairing in solutions of electrolytes in ammonia and amines. This is encouraging since it implies a fairly normal behavior (in the electrolyte sense) for dilute solutions of metals. Further support of the proposed mass action equilibria can be found in the conductance measurements of sodium in NH8 solutions with added salt. Bems, Lepoutre, Bockelman, and Patterson (4) assumed an additional equilibrium between sodium and chloride ions, associated to form NaCl, to compute the concentration of ionic species, monomers, and dimers when the common ion electrolyte is added. Calculated concentrations of conducting species are employed in the Onsager-Kim extension of the conductance theory for low-field conductance of a mixture of ions. Values of [Na]totai ranging from 5 X 10 4 to 6 X 10 2 and of the ratio of NaCl to [Na]totai ranging from zero to 28.5 are included in the calculations. 

A large volume expansion for solutions of sodium in ammonia was first reported by Kraus and Lucasse (17). Since this initial report, many investigations have been made of the volume expansion for a number of alkali metal-ammonia solutions. The techniques employed in these investigations have varied from density measurements for concentrated solutions using the Westphal Balance or Pycnometer to dilatometric studies for dilute solutions, which measure the volume expansion directly. 

Saturated solutions of lithium in ammonia have the lowest density (p = 0.48gcm ) of any known liquid at room temperatme and provide the lowest-temperature liquid metals with a deep pseudoeutectic extending to 88 K. Dissolution of lithium atoms in ammonia produces a rich variety of solvated electronic and ionic species. At very low concentrations (c < 0.01 mole percent metal, MPM),... 

Kraus CA. (1908) Solutions of metals in non-metalHc solvents IV. Material effects accompanying the passage of an electrical current through solutions of metals in liquid ammonia. Migration experiments. J Am Chem Soc 30 1323-1344. 

Both linear and cross-conjugated dienones are reduced by solutions of metals in liquid ammonia. For example, steroidal 4,6-dien-3-ones (Scheme 12) and related compounds are reduced initially to 3,5-dienolates while addition of ammonium chloride to the latter leads to formation of the noncon-... 

Solutions of Metals in Liquid Ammonia and Other Solvents3... 

Hayama S, Skipper NT, Wasse JC, Thompson H (2002) X-ray diffraction smdies of solutions of lithium in ammonia the stmcture of the metal-nonmetal transition. J Chem Phys 116 2991-2996... 

The solutions of metals in liquid ammonia are very good reducing agents, because of the presence of free electrons. 

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