Arsenic/ions/salts

The volatile hydride (arsine in Equation 15.1) is swept by a. stream of argon gas into the inlet of the plasma torch. The plasma flame decomposes the hydride to give elemental ions. For example, arsine gives arsenic ions at m/z 75. The other elements listed in Figure 15.2 also yield volatile hydrides, except for mercury salts which are reduced to the element (Fig), which is volatile. In the plasma flame, the arsine of Equation 15.1 is transformed into As ions. The other elements of Figure 15.2 are converted similarly into their elemental ions. 

The leaching of arsenic forms is usually performed from soil or from tissues of plants or marine animals. The extraction of materials of biological origin typically involves methanol or mixtures of methanol and water. Solutions obtained by centrifugation and filtration are diluted with water and then loaded into an ion-exchange column. The method is applied for assay of arsenic acid salts and arsenosugars, even though they are more easily soluble in water than in methanol. This method of extraction into a solution involves transfer of a smaller quantity of toxic As(III) and As(V) salts than methylated derivatives and AsB or AsC, which are of markedly lower toxicity [88]. 

The geometry and abolute configuration of the (—)5g,-tris(catechol)-arsenate ion have been determined in the potassium salt. The ion has normal octahedral tris-chelate geometry with As-O bonds averaging 1.84 A. The absolute configuration was also determined by the analysis of the c.d. spectrum and the result was corroborative. 

Arsenic species. Arsenite and arsenate ions form the corresponding salts with Cr . Arsenous acid instantly reduces [Cr207] to Cr and, on boiling, precipitates CrAs04. 

Arsenic species. Aqueous Zn is precipitated by arsenite or arsenate ion, forming the corresponding white, gelatinous salts, readily soluble in alkalis and acids, including arsenic acids. 

Solid Compounds. The tripositive actinide ions resemble tripositive lanthanide ions in their precipitation reactions (13,14,17,20,22). Tetrapositive actinide ions are similar in this respect to Ce . Thus the duorides and oxalates are insoluble in acid solution, and the nitrates, sulfates, perchlorates, and sulfides are all soluble. The tetrapositive actinide ions form insoluble iodates and various substituted arsenates even in rather strongly acid solution. The MO2 actinide ions can be precipitated as the potassium salt from strong carbonate solutions. In solutions containing a high concentration of sodium and acetate ions, the actinide ions form the insoluble crystalline salt NaM02(02CCH2)3. The hydroxides of all four ionic types are insoluble ... 

In metallic form, barium is very reactive, reacting readily with water to release hydrogen. In aqueous solution it is present as an ion with a +2 charge. Barium acetate, chloride, hydroxide, and nitrate are water-soluble, whereas barium arsenate, chromate, duoride, oxalate, and sulfate are not. Most water-insoluble barium salts dissolve in dilute acids barium sulfate, however, requkes strong sulfuric acid. 

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. 

If the dissociation constant of the acid HA is very small, the anion A- will be removed from the solution to form the undissociated acid HA. Consequently more of the salt will pass into solution to replace the anions removed in this way, and this process will continue until equilibrium is established (i.e. until [M + ] x [A-] has become equal to the solubility product of MA) or, if sufficient hydrochloric acid is present, until the sparingly soluble salt has dissolved completely. Similar reasoning may be applied to salts of acids, such as phosphoric(V) acid (K1 = 7.5 x 10-3 mol L-1 K2 = 6.2 x 10-8 mol L-1 K3 = 5 x 10 13 mol L-1), oxalic acid (Kx = 5.9 x 10-2 mol L-K2 = 6.4 x 10-5molL-1), and arsenic)V) acid. Thus the solubility of, say, silver phosphate)V) in dilute nitric acid is due to the removal of the PO ion as... 

Antimony pyrogallate, Sb(C6H503). Antimony(III) salts in the presence of tartrate ions may be quantitatively predpitated with a large excess of aqueous pyrogallol as the dense antimony pyrogallate. The method fadlitates a simple separation from arsenic the latter element may be determined in the filtrate from the predpitation of antimony by direct treatment with hydrogen sulphide. 

Sulphuric acid is not recommended, because sulphate ions have a certain tendency to form complexes with iron(III) ions. Silver, copper, nickel, cobalt, titanium, uranium, molybdenum, mercury (>lgL-1), zinc, cadmium, and bismuth interfere. Mercury(I) and tin(II) salts, if present, should be converted into the mercury(II) and tin(IV) salts, otherwise the colour is destroyed. Phosphates, arsenates, fluorides, oxalates, and tartrates interfere, since they form fairly stable complexes with iron(III) ions the influence of phosphates and arsenates is reduced by the presence of a comparatively high concentration of acid. 

The ability of metal ions to form complexes with formazans is utilized to determine these ions either directly (for low valent reducing ions) or indirectly in the presence of a reducing agent. Among others, molybdenum(VI) and vanadium(V) have been determined using this method.442,443 Indirect methods have been reported for the analyses of substances that do not reduce tetrazolium salts. Examples include arsenic in nickel ores436 and traces of selenium.437 A method for the extraction and analysis of a number of metal ternary ion association complexes has been described.444 - 448... 

The mobility of arsenic compounds in soils is affected by sorp-tion/desorption on/from soil components or co-precipitation with metal ions. The importance of oxides (mainly Fe-oxides) in controlling the mobility and concentration of arsenic in natural environments has been studied for a long time (Livesey and Huang 1981 Frankenberger 2002 and references there in Smedley and Kinniburgh 2002). Because the elements which correlate best with arsenic in soils and sediments are iron, aluminum and manganese, the use of Fe salts (as well as Al and Mn salts) is a common practice in water treatment for the removal of arsenic. The coprecipitation of arsenic with ferric or aluminum hydroxide has been a practical and effective technique to remove this toxic element from polluted waters... 

SWV has been applied to study electrode reactions of miscellaneous species capable to form insoluble salts with the mercury electrode such as iodide [141,142], dimethoate pesticide [143], sulphide [133,144], arsenic [145,146], cysteine [134, 147,148], glutathione [149], ferron (7-iodo-8-hydroxyquinolin-5-sulphonic acid) [150], 6-propyl-2-thiouracil (PTU) [136], 5-fluorouracil (FU) [151], 5-azauracil (AU) [138], 2-thiouracil (TU) [138], xanthine and xanthosine [152], and seleninm (IV) [153]. Verification of the theory has been performed by experiments at a mercury electrode with sulphide ions [133] and TU [138] for the simple first-order reaction, cystine [134] and AU [138] for the second-order reaction, FU for the first-order reaction with adsorption of the ligand [151], and PTU for the second-order reaction with adsorption of the ligand [137]. Figure 2.90 shows typical cathodic stripping voltammograms of TU and PTU on a mercuiy electrode. The order of the... 

For removing low levels of priority metal pollutants from wastewater, using ferric chloride has been shown to be an effective and economical method [41]. The ferric salt forms iron oxyhydroxide, an amorphous precipitate in the wastewater. Pollutants are adsorbed onto and trapped within this precipitate, which is then settled out, leaving a clear effluent. The equipment is identical to that for metal hydroxide precipitation. Trace elements such as arsenic, selenium, chromium, cadmium, and lead can be removed by this method at varying pH values. Alternative methods of metals removal include ion exchange, oxidation or reduction, reverse osmosis, and activated carbon. 

Dimercaprol (BAL, British Anti-Lewisite) was developed in World War 11 as an antidote against vesicant organic arsenicals (B). It is able to chelate various metal ions. Dimercaprol forms a liquid, rapidly decomposing substance that is given intramuscularly in an oily vehicle. A related compound, both in terms of structure and activity, is di-mercaptopropanesulfonic acid, whose sodium salt is suitable for oral administration. Shivering, fever, and skin reactions are potential adverse effects. 

Molecular recognition, calmodulin, 46 447 Mollusks, arsenic in, 44 150, 167, 168, 170 Molten salts electrolysis, 31 11 oxygen activation, 44 328-329 Molybdate ions, tetrahedral, 39 194-195 Molybdenite, 17 108 Molybdenum, 45 1 acetylene complexes of, 4 104 alkoxides... 

The trivaleney of the complex ion, [Pt(NH3)5Cl] , is confirmed by conductivity measurements, the chloride having conductivity 404 at 1000 litres dilution, and by the power of the salts to coagulate colloidal solutions of arsenic trisulphide. 

Clearly there is much to be learned from further examination of arsenic levels in seawater and porewaters. However, low concentrations and analytical difficulties presented by the salt matrix continue to complicate these analyses (33, 85). Techniques such as HPLC/ICP-MS suffer from interference by the molecular ion 40Ar35Cl +, formed by combination of the plasma gas and chloride ion, with the monoisotopic 75As+. Techniques to separate the arsenic compounds from the salt matrix before HPLC/ICP-MS have not been fully investigated because they may result in fractionation of the compounds and loss of speciation information. Nevertheless, methods to establish the presence or otherwise in seawater of some of the arsenic-containing compounds important in other marine compartments is worth pursuing. 

The action of strong aprotic Lewis acids (antimony(V) fluoride, arsenic(V) fluoride etc.) provokes the ionization of xenon difluoride, leading to the formation of fluoroxenonium salts XcF + MFn or Xe2F3 MFn less strong acceptors of the fluoride ion (hydrogen fluoride, boron trifluoride, etc.) polarize the xenon difluoride molecule. 

Aqueous solutions of molybdate and arsenate, pH 3-5, contain [AsMo903i(H20)3]3 and an As2Mo6 anion.71 The exact structure of the latter ion in solution is in some doubt, although the tetramethylammonium sodium salt contains the anion shown in Figure 15. Low angle X-ray scattering measurements of aqueous molybdoarsenate solutions are not compatible with this structure and the anion may be hydrated in a fashion similar to that observed for the analogous... 

As mentioned in Chapter II, many metallic arsenides are found in Nature. Arsenic combines directly with most metals to form stable compounds, those of the heavy metals being the most stable. The latter may be obtained by allowing an aqueous solution of a salt of the appropriate metal to drop into an atmosphere of arsine, air being completely absent, and the vessel continually shaken.1 Precipitation by passing arsine into the salt solution is not satisfactory as, in the case of copper, silver, gold, mercury and lead, a secondary reaction with the excess of metallic ions occurs ... 

---