Dissolution in acids

The impurities in ordinary iron assist dissolution in acid, and are responsible for the characteristic smell of the hydrogen from this source.) In dilute nitric acid, ammonium nitrate is formed ... 

Cobalt(Il) dicobalt(Ill) tetroxide [1308-06-17, Co O, is a black cubic crystalline material containing about 72% cobalt. It is prepared by oxidation of cobalt metal at temperatures below 900°C or by pyrolysis in air of cobalt salts, usually the nitrate or chloride. The mixed valence oxide is insoluble in water and organic solvents and only partially soluble in mineral acids. Complete solubiUty can be effected by dissolution in acids under reducing conditions. It is used in enamels, semiconductors, and grinding wheels. Both oxides adsorb molecular oxygen at room temperatures. 

Dremlyuzhenko SG, Voloshchuk AG, Zakharuk Zl, Yurijchuk IN (2008) Thermodynamic evaluation and potentiometric study of Cdi xMnxTe and Cdi xZnx Te dissolution in acid and alkaline solutions. Inorg Mater 44 21-29... 

It is found that the dissolution of zinc sulfides occurs more rapidly when they are in contact with copper sulfide or iron sulfide than when the sulfides of these types are absent. This enhancement is brought about by the formation of a galvanic cell. When two sulfide minerals are in contact, the condition for dissolution in acidic medium of one of the sulfides is that it should be anodic to the other sulfide in contact. This is illustrated schematically in Figure 5.3 (A). Thus, pyrite behaves cathodically towards several other sulfide minerals such as zinc sulfide, lead sulfide and copper sulfide. Consequently, pyrite enhances the dissolution of the other sulfide minerals while these minerals themselves understandably retard the dissolution of pyrite. This explains generally the different leaching behavior of an ore from different locations. The ore may have different mineralogical composition. A particle of sphalerite (ZnS) in contact with a pyrite particle in an aerated acid solution is the right system combination for the sphalerite to dissolve anodically. The situation is presented below ... 

Fig. 5.54 Mixed potential. (A) Zinc dissolution in acid medium. The partial processes are indicated at the corresponding voltammograms. (B) Dissolution of mercury in nitric acid solution. The original dissolution rate characterized by (1) the corrosion current y a is enhanced by (2) stirring which causes an...

Air (particulate lead) Collection of sample onto filter addition of206Pb to filter dissolution of filter in NaOH acidification separation of lead by electrodeposition dissolution in acid IDMS 0.1 ng/m3 No data Volkening et al. 1988... 

Grains, milk mussel, fish Bomb digestion of sample with acid and heat or digestion with acid and dry ashing dissolution in acid dilution with water GFAAS 20 pg/g (bomb) 5 pg/g (dry ash) No data 85-107 75-107 Ellen and Van Loon 1990... 

This would give rise to two semicircles in the complex plane, as discussed above, together, possibly, with a Warburg region if this can be resolved. In fact this behaviour is indeed seen close to the onset of iron dissolution in acidic media but at slightly higher potentials. As the local concentration of Fe(II) rises near the electrode, formation of insoluble Fe(OH)2 takes place as ... 

Table 4. Chemical composition (in ni%) of the sandy clay I<250 pun), non-carbonate portion (NCPl of typical Estonian kukersiie after dissolution in acid and of ashed kukersiie oil shale f...

Energies of Activation. Low E values (<42 kJ mol-1) usually indicate diffusion-controlled processes whereas higher E values indicate chemical reaction processes (Sparks, 1985, 1986). For example, E values of 6.7-26.4 kJ mol-1 were found for pesticide sorption on soils and soil components (Haque et al., 1968 Leenheer and Ahlrichs, 1971 Khan, 1973) while gibbsite dissolution in acid solutions was characterized by E values ranging from 59 4.3 to 67 0.6 kJ mol-1 (Bloom and Erich, 1987). 

As mentioned earlier, the dissolution of oxides and hydroxides, like feldspars and ferromagnesian minerals, appears to be a surface-controlled reaction. One indication of this is the high E values found by several investigators. Bloom and Erich (1987) obtained E values ranging from 59 4.3 to 67 0.6 kj mol"1 for gibbsite dissolution in acid solutions (pH 1.5-4.0). These values are much higher than for diffusion-controlled reactions reported earlier. 

Jedlicka A, Grafnetterova T, Miller V. 2003. HPLC method with UV detection for evaluation of digoxin tablet dissolution in acidic medium after solid-phase extraction. J. Pharm. Biomed. Anal. 33 109 115. 

The mechanism given for dissolution in acid solution applies also in neutral solutions, but with the modification that 0FeOH (assumed to correspond to the condition 6 < 1 above) changes to 0-1. 

The main properties of the solid are the texture, the nature of functional groups (e.g., the number and strength of the acidic and basic centers,the isoelectric point), the presence of exchangeable ions, and the reactivity (surface dissolution in acidic or basic solution, etc.). 

Figure 22 Three-compartment cell for studies of the kinetics of iron dissolution in acid.

Pentathiazyl tetrachloroaluminate(l —) and, to a lesser extent, penta-thiazyl tetrachloroferrate(l —) are moisture-sensitive both are soluble in thionyl chloride, anhydrous formic acid, and concentrated sulfuric and nitric acids. On dissolution in acid, hydrogen chloride is evolved because of decomposition of the anion. The solution in anhydrous formic acid can be used to prepare other salts by metathesis.7 The hexachloroantimonate(l —) undergoes almost no reaction when exposed to water or moist air for 24 hr. 

Unless the sample is readily soluble in water, the solution is unsuitable for testing for anions, as during dissolution in acids some of these might decompose. For the test for anions we can use either the aqueous solution, or, if the sample is not soluble in water, sodium carbonate extract should be prepared either from the whole of the sample, or the sample should first be extracted with hot water and the residue treated with sodium carbonate. This procedure is described in detail in Section V.18. 

Lemery defined precipitation as an expression chemists used to describe the fall of a body which had been suspended dissolved in a liquid from which it has been subsequently disunited. Although Fontenelle construed this as a physical definition based on the principles of hydrostatics, Lemery used it to differentiate true metallic precipitates, or the products of displacement reactions, from false ones. One could obtain false precipitates, or the matters that lost their initial metallic form and were reduced to a friable and indissoluble mass, in several ways. Calcination (red and violet mercury), incomplete dissolution in acids (antimony in spirit of salt or in regal water), and calcination after dissolution and evaporation (mercury in spirit of niter), all produced such precipitates. True metallic precipitates differed from false ones in that they were directly separated from their dissolution in liquid. As Lemery put it, false precipitates were abandoned by the liquid, while true precipitates abandoned the liquid themselves. True precipitates were made sometimes naturally through agitation, but mostly with recourse to the intermediates such as alkali salts or other metals. The choice of intermediates depended on the nature of the bodies to be precipitated. Lemery provided an exhaustive discussion for each case. In order to precipitate a resinous matter dissolved in spirit of wine, one could use common water which, by meshing intimately with the spirit, would precipitate the resinous matter. Camphor in spirit of wine could thus be... 

The fourth class of phenomena, the precipitation of metals from their dissolution in acids by fixed and volatile alkali salts, was Louis Lemery s main interest. This was precisely the problem his father had labeled as one of the most difficult questions to resolve well in philosophy already in 1675. This type of precipitation consisted yet of two kinds. In the first, the metal dissolved in acid was precipitated as subtle powder by an alkali. In the second, the metallic solution turned, upon the mixture... 

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