Sulfide base-insoluble

Group 3. Base-insoluble sulfides and hydroxides After the solution is filtered to remove any acid-insoluble sulfides, it is made slightly basic, and (NH4)2S is added. In basic solutions the concentration of is higher than in acidic solutions. Thus, the ion products for many of the more soluble sulfides are made to exceed their K p values and precipitation occurs. The metal ions precipitated at this stage are Al +, Cr Fe +, Zn +, Ni +, Co +, and Mn + (The Al +, and Cr ions do not form insoluble sulfides instead they precipitate as insoluble hydroxides, as Figure 17.23 shows.)... 

The analyses for individual ions in fhe acid-insoluble and base-insoluble sulfides are a bit more complex, but the same general principles are involved. The detailed procedures for carrpng out such analyses are given in many laboratory manuals. 

To detect free alkali in the presence of alkali sulfides, which also give an alkaline reaction owing to hydrolysis, use is made of the fact that thallous sulfide is insoluble whereas thallous hydroxide is soluble in water and is almost as strong a base as potassium hydroxide. Free alkali may be detected by adding neutral thallous nitrate and then testing the solution for an alkaline reaction. 

It is good practice to keep concentrations of airborne nickel in any chemical form as low as possible and certainly below the relevant standard. Local exhaust ventilation is the preferred method, particularly for powders, but personal respirator protection may be employed where necessary. In the United States, the Occupational Safety and Health Administration (OSHA) personal exposure limit (PEL) for all forms of nickel except nickel carbonyl is 1 mg/m. The ACGIH TLVs are respectively 1 mg/m for Ni metal, insoluble compounds, and fume and dust from nickel sulfide roasting, and 0.1 mg/m for soluble nickel compounds. The ACGIH is considering whether to lower the TLVs for all forms of nickel to 0.05 mg/m, based on nonmalignant respiratory effects in experimental animals. 

Thiosulfates. The ammonium, alkaU metal, and aLkaline-earth thiosulfates are soluble in water. Neutral or slightly alkaline solutions containing excess base or the corresponding sulfite are more stable than acid solutions. Thiosulfate solutions of other metal ions can be prepared, but their stabiUty depends on the presence of excess thiosulfate, the formation of complexes, and the prevention of insoluble sulfide precipitates. 

Compounds of Tl have many similarities to those of the alkali metals TIOH is very soluble and is a strong base TI2CO3 is also soluble and resembles the corresponding Na and K compounds Tl forms colourless, well-crystallized salts of many oxoacids, and these tend to be anhydrous like those of the similarly sized Rb and Cs Tl salts of weak acids have a basic reaction in aqueous solution as a result of hydrolysis Tl forms polysulfldes (e.g. TI2S3) and polyiodides, etc. In other respects Tl resembles the more highly polarizing ion Ag+, e.g. in the colour and insolubility of its chromate, sulfide, arsenate and halides (except F), though it does not form ammine complexes in aqueous solution and its azide is not explosive. 

The compounds HgaY2X2 (Y = S, Se, Te X = Cl, Br, I) are insoluble in water, dilute acids, and cone. HCl, and they are not attacked by these solvents. Cone. HNO3 converts the sulfide chloride into the sulfide nitrate HgsSalNOsla (20, 290). With bases, rapid decomposition occurs, leading to the formation of oxide chacogenides (20), or a mixture of oxide and chalcogenide (111), a matter on which agreement has not yet been reached. 

Other examples of this synthetic strategy are known for example, a recent zirconium polymer by Illingsworth and Burke (8), who joined amine side groups of a zirconium bis(quadridentate Schiff-base) with an acid dianhydride to give amide linkages. Once again, caution is necesary, as Jones and Power (2) learned when they attempted to link metal bisO-diketonates) with sulfur halides that is, they obtained insoluble metal sulfides because the p-diketone complexes which they used were fairly labile and the insolubility drove the reactions to completion in the wrong direction. 

Cu may be reduced to Cu", especially if soft bases such as halides and S are present to stabilize the Cu" " ion. All are chalcophiles and tend to form insoluble sulfides in anaerobic conditions (pKs = 21.3-25.6, 19.4-26.6 and 36.1, respectively). They therefore tend to have low mobilities in submerged soils, especially Cu +, and accumulate. 

Most base-metal sulfides are very insoluble compounds and, in principle, processes based on the differences in their solubilities can be used in the selective precipitation of sulfides. For example, the strong affinity of copper ions for sulfide ion is used to good effect in the removal of traces of copper from leach liquors in the recovery of nickel,406 cobalt407 and manganese.408 For manganese, other impurity metal ions such as cobalt, nickel and zinc are also selectively precipitated by the use of sulfide ions. 

Ray et al. [77] used an indirect method based on AAS for the determination of sulfide in flooded acid sulfate soils. Hydrogen sulfide, evolved during the anaerobic metabolism of sulfate, is readily converted into insoluble metal sulfides, chiefly iron sulfide, in flooded acid sulfate soils. A method for determining sulfide is based on the precipitation of the sulfide as zinc sulfide and subsequent determination by methylene blue formation or iodine titrimetry. 

In operationally defined speciation the physical or chemical fractionation procedure applied to the sample defines the fraction isolated for measurement. For example, selective sequential extraction procedures are used to isolate metals associated with the water/acid soluble , exchangeable , reducible , oxidisable and residual fractions in a sediment. The reducible, oxidisable and residual fractions, for example, are often equated with the metals associated, bound or adsorbed in the iron/manganese oxyhydroxide, organic matter/sulfide and silicate phases, respectively. While this is often a convenient concept it must be emphasised that these associations are nominal and can be misleading. It is, therefore, sounder to regard the isolated fractions as defined by the operational procedure. Physical procedures such as the division of a solid sample into particle-size fractions or the isolation of a soil solution by filtration, centrifugation or dialysis are also examples of operational speciation. Indeed even the distinction between soluble and insoluble species in aquatic systems can be considered as operational speciation as it is based on the somewhat arbitrary definition of soluble as the ability to pass a 0.45/Am filter. 

Zinc oxide (ZnO), which is produced by burning zinc vapor in atmospheric oxygen, is by far the most important compound of zinc. Under the name of zinc white, the oxide is used as a paint pigment. It is also used as a base in the manufacture of enamels and glass, and as a ruler in the fabrication of automobile tires and other kinds of rubber goods. Zinc sulfide (ZnS) is also an important white paint pigment which is used either as such or in the form of lithopone, which is a mixture of zinc sulfide and barium sulfate. This widely used pigment is prepared by the metathetical reaction between zinc sulfate and barium sulfide, a reaction in which both of the products are insoluble ... 

Based on the analyses of the trace contaminants conducted on the wheat millfeed-derived products, numerous potential problem components were identified, relative to catalyst activity (3). These components (shown in Table 1) include sulfate (potential for metal sulfide formation) calcium, magnesium, and phosphate (potential for catalyst pore plugging by insoluble salt precipitation) sodium or potassium (alkali attack on the catalyst support) organic nitrogen components, such as amino acids (thiol... 

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