Precipitate sulfide group precipitates

If the various metals are present in a solution which has been acidified with 6.3 N hydrochloric acid, some of the metal ions precipitate as sulfides and others do not. The metal ions that precipitate as sulfides under these conditions are Hg+-, Cu+, Cd++, Sn++, Sn+ + + +, As+ + +, AS+ + + ++, Sb+ + +, Sb+ + + + -, and Bi+ ++. The solubility products for the corresponding sulfides, HgS, CuS, CdS, PbS, SnS, SnSs, AsgSg, AsoS,v SboSjj, SboS and BigSg, have values corresponding to precipitation under these conditions. These metals are said to constitute the hydrogen sulfide group in the system of qualitative analysis. 

Sources such as Riffault et al. (1874) and Heaton (1928) describe the composition of an antimony vermilion as a red form of antimony sulfide. This generally seems to be prepared by precipitation from the chloride, for example, Gettens and Stout (1966) state that synthesis is by precipitating antimony chloride with sodium thiosulfate or with hydrogen sulfide. It was apparently introduced as a pigment by Murdoch in 1847. See Antimony sulfides group for a fuller discussion of the likely composition. 

Heaton (1928) reports that when synthetic zinc sulfide was prepared by precipitation it gave a white substance of great opacity . Supposedly introduced as a pigment in 1852, it was not widely used because of a grey cast caused by traces of iron sulfide group (. v.) compounds. A purer product was marketed from 1927 under the trade name Sachtolith this also contained 3% zinc oxide q.v.). According to the Merck Index (1996), synthetic zinc sulfide often contains 15-20% water of hydration it is therefore heated in the absence of air to 725°C to convert it to wurtzite, the hexagonal form of ZnS preferred by the paint industry. 

Inorganic Analysis The most important precipitants for inorganic cations are chromate, the halides, hydroxide, oxalate, sulfate, sulfide, and phosphate. A summary of selected methods, grouped by precipitant, is shown in Table 8.1. Many inorganic anions can be determined using the same reactions by reversing the analyte... 

In another process for the synthesis of PPS, as well as other poly(arylene sulfide)s and poly(arylene oxide)s, a pentamethylcyclopentadienylmthenium(I) TT-complex is used to activate -dichlorobenzene toward displacement by a variety of nucleophilic comonomers (92). Important facets of this approach, which allow the polymerization to proceed under mild conditions, are the tremendous activation afforded by the TT-coordinated transition-metal group and the improved solubiUty of the resultant organometaUic derivative of PPS. Decomplexation of the organometaUic derivative polymers may, however, be compHcated by precipitation of the polymer after partial decomplexation. 

Arsenic may be detected quaUtatively as a yellow sulfide, AS2S2, by precipitation from a strongly acidic HQ solution. Other members of this group... 

Group II consists of six different cations, all of which form very insoluble sulfides (Figure A). These compounds are precipitated selectively by adding hydrogen sulfide, a toxic, foul-smelling gas. at a pH of 0.5. At this rather high H+ ion concentration. 0.3 M, the equilibrium... 

Group III sulfides are much more difficult to precipitate than those of Group II. Compare, for example, the equilibrium constant for the reaction... 

Group III sulfides and hydroxides. /Left) Five Group III cations precipitatB as sulfides. These are NiS. CoS. and FeS (all of which are black], MnS (salmon), and ZnS (white). (Right) Jvio cations precipitate as hydroxides. AIIOHfo (white) and Cr(0H)3 (gray-green). 

Group IV cations have soluble chlorides and sulfides, so they are still in solution at this point. The alkaline earth cations (Mg2, Ca2+. Ba2+) are precipitated as carbonates... 

Figure 4.23. Comparison of results on four batches using four different methods. The results are grouped according to batch, and within a group, the methods are sulfide precipitation, polarography. X-ray fluorescence, and inductively coupled plasma absorption (left to right).

Hydrogen sulfide gas is used in analytical chemistry laboratories to detect certain metal ions in a solution. If the solution contains a Group IIA metal, such as calcium, a precipitate will form when an acidic solution containing hydrogen sulfide is added to it. The precipitate forms because one of the products of the chemical reaction is insoluble (which means it does not dissolve). 

Group IIIA metals, however, like aluminum, will not precipitate in an acidic hydrogen sulfide solution. They will precipitate, however, if a basic hydrogen sulfide solution is introduced. Group LA metals, on the other hand, are always soluble in a hydrogen sulfide solution, regardless of whether the solution is acidic or... 

During the traditional qualitative inorganic analytical procedure, samples containing the lead and salicylate radicals can lead to the formation and possible detonation of lead picrate. This arises dining evaporation of the filtrate with nitric acid, after precipitation of the copper-tin group metals with hydrogen sulfide. Salicylic acid is converted under these conditions to picric acid, which in presence of lead gives explosive lead picrate. An alternative (MAQA) scheme is described which avoids this possibility. 

Section 2.17). We shall find that it dominates much of life s organic chemistry too. There is also the rather unusual insolubility of VS4. We need to explain the presence of some V, Co, Ni and Zn in early life, but note that their sulfides are relatively soluble in somewhat acid solutions, pH < 7, which may have prevailed at least locally some 4 x 109 years ago. Molybdenum and heavy metals of Groups 13 to 16 are also insoluble as sulfides but tungsten does not precipitate so easily and is known to be more available than molybdenum in sulfide-rich seas. 

Cys(SBu-f)Gly [Reductive Deprotection of Boc and tert-Butyl Ester Groups in the Presence of a tert -Butyl Sulfide].307 Boc Cys(SBu-t)Gly OBu-t (1 mmol) was stirred with TFA (13 mmol), CH2C12 (32 mmol), and Et3SiH (2.5 mmol) at room temperature for 1.5 hours. After solvent removal, the residue was triturated with Et20 and the precipitated product was removed by filtration, washed with Et20, and dried 100%. 

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