Ammonium salts dissolving metals

Ammonium salts dissolve metal oxides, hydroxides in liquid ammonia (similar to reactions of basic oxides and hydroxides by an acid). 

An important example related lo the atmospheric aerosol is the droplet containing dissolved sulfates that form as a result of the oxidation of SO2 in solution. The sulfates may be present a.s sulfuric acid or in a partially neutralized form as ammonium salts or metallic salts from sources such as flyash. The droplet size distribution and chemical composition are determined by a combination of thermodynamic and rate processes. In this section, we consider only equilibrium thermodynamics as it affects the vapor pressure of the drop. 

When it is recalled that the ammonium ion is simply NH3 that has gained a proton, it is clear that NH4+ is the conjugate acid of NH3. Therefore, it is not unusual to expect NH4+ to behave as an acid, which was illustrated in Eq. (9.16). However, the NH4+ ion can react as an acid under other conditions. When an ammonium salt such as NH4C1 is heated to the melting point, the salt becomes acidic. In fact, the reactions are similar to those that HC1 would give. For example, metals dissolve with the release of hydrogen ... 

Upon dissolving the copolymer/catalyst mixture in ethylbutylamine (EtBuNH) the introduction of CO2 at atmospheric pressure results in formation of an equilibrium mixture of carbamic acid and the quaternary ammonium salt of carbamate. The carbamic acid serves to remove the copolymer from the metal center, at which time it precipitates in the ionic liquid and is isolated by filtration. The metal catalyst... 

The protonic concept of acid and bases is applicable to many of these high lemperatures solvent systems such as the fused ammonium salts which possess the oniunt ion or solvated proton, and the fused anionic acids which arc salts possessing a metallic ion and a hydrogen containing anion. One of the most useful of the anionic acids is KHF which is used to dissolve ore minerals containing silica, tilania and other refractory oxides. 

Other examples of reported molecular complexes are tabulated in Refs. 202,506, and 507. However, it is necessary to note that the participation in these syntheses of acids, ammonium salts, halogens, and alkyl halides [506,507,551,562] provokes doubts in respect of determining the role of the electrochemical processes, since the reagents above can themselves dissolve elemental metals in various liquid media, forming coordination compounds (Sec. 3.4.3). 

TJranyl nitrate forms double salts of the type E U02(N03)3, where R =K, NH4, Rb, Cs, or Tl. They may be prepared by crystallising a solution of the mixed nitrates in concentrated nitric acid or by crystallisation from a solution of the alkali uranate in excess of nitric acid. The crystals are all anhydrous, and in the case of the potassium salt are orthorhombic, whilst the rubidium and caesium salts are rhombo-hedral and isomorphous with each other. The ammonium salt yields both orthorhombic and rhombohedral crystals. All exhibit a yellowish-green fluorescence they are liygroscopic and readily decomposed by water into their components. The thallium salt is particularly unstable, being decomposed in moist air. On the other hand, the rubidium salt dissolves in water at 80° C. without decomposition. The corresponding salts of sodium, lithium, or of divalent metals have not been prepared. 

Uranium minerals may be obtained in solution, in a suitable condition for estimation, by the following process. The ore is dissolved in aqua regia, or, if necessary, fused with alkali bisulphate and extracted mth hot hydrochloric acid. After evaporation to drjmess, the residue is taken up with dilute hydrochloric acid, and the solution saturated with hydrogeir sulphide in order to remove any copper, lead, bismuth, arsenic, antimony, or any other metal yielding an insoluble sulphide. The filtrate is concentrated and treated with ammonium carbonate, which precipitates the carbonates of the alkaline earths, iron, and most of the rare earths. The filtrate is neutralised by hydrochloric acid, evaporated to dryness, and the residue ignited to drive off ammonium salts, and then redissolved in dilute acid. The remaining rare earths, and particularly thorium, are next precipitated by the addition of oxalic acid. The filtrate, which contains the uranium in the uranyl condition, may now be precipitated by any of the methods described above. 

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