Aqueous solutions metal compounds

In many cases the desired compound is not the only one which can be formed in solution. In that case competitive precipitation of several compounds may take place [128], In aqueous solutions, metal hydroxides or oxides are the most common ones. If we consider again the case of CdS, the solubility product of Cd(OH)2 (Ks = 10 - ) corresponds to the equilibrium ... 

In addition to these preparations in aqueous solution, the compound has also been prepared in low yield by the action of nitrosyl chloride at 100° on platinum. This low yield is due to incomplete reaction and the difficulty of separating the deliquescent powder from the unreacted metal. It is possible to prepare the compound in higher yield by the action of nitrosyl chloride on platinum(II) or platinum(IV) chloride. Neither platinum(II) nor platinum(IV) chloride is readily obtained commercially. Furthermore, platinum(IV) chloride is quite hygroscopic and is difficult both to prepare and to handle. 

These reactions take place in ammonia just as in an aqueous solution. The compound of low solubility product is precipitated. Most chlorides, (except of Na, NH, Be) sulphides, bromides, iodides are insoluble in liquid ammonia while metal nitrates are soluble in liquid anunonia. In many cases, the direction of the reaction is reversed in liquid ammonia. For example, in aqueous solution... 

In aqueous solutions, organic compounds normally have some inhibition effect on metals. For example, it has been found [33] that simple sodium linear-saturated carboxylates can effectively inhibit the corrosion of a magnesium... 

In contrast to the + 2 state, copper(I) compounds are less frequently coloured and are diamagnetic, as expected since the 3d level is full. However, the copper(I) ion, unlike copper(II), is unstable in aqueous solution where it disproportionates into copper(II) and copper(O) (i.e. copper metal). 

Table 14.2 shows that all three elements have remarkably low melting points and boiling points—an indication of the weak metallic bonding, especially notable in mercury. The low heat of atomisation of the latter element compensates to some extent its higher ionisation energies, so that, in practice, all the elements of this group can form cations in aqueous solution or in hydrated salts anhydrous mercuryfll) compounds are generally covalent. 

In preparing an aqueous sol ution of a diazonium salt, such as benzene-diazonium chloride, it is usual to dissolve the amine in a slight excess (about 2 2 molecular equivalents) of dilute hydrochloric acid (or alternatively to dissolve the crystalline amine hydrochloride in i 2 equivalents of the acid) and then add an aqueous solution of a metallic nitrite. Nitrous acid is thus generated in situ, and reacts with the amine salt to give the diazonium compound. For a successful preparation of an aqueous solution of the diazonium salt, however, two conditions must always be observed ... 

The aromatic shifts that are induced by 5.1c, 5.If and S.lg on the H-NMR spectrum of SDS, CTAB and Zn(DS)2 have been determined. Zn(DS)2 is used as a model system for Cu(DS)2, which is paramagnetic. The cjkcs and counterion binding for Cu(DS)2 and Zn(DS)2 are similar and it has been demonstrated in Chapter 2 that Zn(II) ions are also capable of coordinating to 5.1, albeit somewhat less efficiently than copper ions. Figure 5.7 shows the results of the shift measurements. For comparison purposes also the data for chalcone (5.4) have been added. This compound has almost no tendency to coordinate to transition-metal ions in aqueous solutions. From Figure 5.7 a number of conclusions can be drawn. (1) The shifts induced by 5.1c on the NMR signals of SDS and CTAB... 

Aqueous solutions of caustic soda aie highly alkaline. Hence caustic soda is ptimatily used in neutralization reactions to form sodium salts (79). Sodium hydroxide reacts with amphotoric metals (Al, Zn, Sn) and their oxides to form complex anions such as AlO, ZnO. SnO ", and (or H2O with oxides). Reaction of AI2O2 with NaOH is the primary step during the extraction of alumina from bauxite (see Aluminum compounds) ... 

The first reported synthesis of acrylonitrile [107-13-1] (qv) and polyacrylonitrile [25014-41-9] (PAN) was in 1894. The polymer received Htde attention for a number of years, until shortly before World War II, because there were no known solvents and the polymer decomposes before reaching its melting point. The first breakthrough in developing solvents for PAN occurred at I. G. Farbenindustrie where fibers made from the polymer were dissolved in aqueous solutions of quaternary ammonium compounds, such as ben2ylpyridinium chloride, or of metal salts, such as lithium bromide, sodium thiocyanate, and aluminum perchlorate. Early interest in acrylonitrile polymers (qv), however, was based primarily on its use in synthetic mbber (see Elastomers, synthetic). 

In aqueous solutions Sbp3 reacts with many metal fluorides to form compounds such as MSbF where M = Li [72121 -39-2] Na [34109-83-6] K [15273-81-1], Cs [36195-09-0], [54189-44-5], andM2Sbp3 where M = K [20645-41-4], Cs [40902-54-3], 2md5 5lJ32516-50-0]. In addition,... 

Another method of removing mercury compounds from aqueous solution is to treat them with water-soluble reducing agents, thus hberating metallic mercury (26). The use of formaldehyde (qv) at a pH of 10—12 also is recommended. 

When an aqueous effluent stream containing organomercurials cannot be recycled, it may be treated with chlorine to convert the organomercury to inorganic mercury. The inorganic compounds thus formed are reduced to metallic mercury with sodium borohydride. The mercury metal is drained from the reactor, and the aqueous solution discarded. The process utilising sodium borohydride is known as the Ventron process (27). 

Electrowinning from Aqueous Solutions. Electrowinriing is the recovery of a metal by electrochemical reduction of one of its compounds dissolved in a suitable electrolyte. Various types of solutions can be used, but sulfuric acid and sulfate solutions are preferred because these are less corrosive than others and the reagents are fairly cheap. From an electrochemical viewpoint, the high mobiUty of the hydrogen ion leads to high conductivity and low ohmic losses, and the sulfate ion is electrochemicaHy inert under normal conditions. 

The most common oxidation state of niobium is +5, although many anhydrous compounds have been made with lower oxidation states, notably +4 and +3, and Nb can be reduced in aqueous solution to Nb by zinc. The aqueous chemistry primarily involves halo- and organic acid anionic complexes. Virtually no cationic chemistry exists because of the irreversible hydrolysis of the cation in dilute solutions. Metal—metal bonding is common. Extensive polymeric anions form. Niobium resembles tantalum and titanium in its chemistry, and separation from these elements is difficult. In the soHd state, niobium has the same atomic radius as tantalum and essentially the same ionic radius as well, ie, Nb Ta = 68 pm. This is the same size as Ti ... 

Nloha.tes, Niobic acid is amphoteric and can act as an acid radical in several series of compounds, which are referred to as niobates. Niobic acid is soluble in solutions of the hydroxides of alkaH metals to form niobates. Fusion of the anhydrous pentoxide with alkaH metal hydroxides or carbonates also yields niobates. Most niobates are insoluble in water with the exception of those alkaH metal niobates having a base-to-acid ratio greater than one. The most weU-known water-soluble niobates are the 4 3 ad the 7 6 salts (base acid), having empirical formulas MgNb O c, (aq) and M24Nb2202y (aq), respectively. The hexaniobate is hydrolyzed in aqueous solution according to the pH-dependent reversible equiHbria (130), when the pH is ca 9. 

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