Acid, arsenious

The chromic acid oxidation of As(III) was first studied by De Lury, whose results have been recalculated by Westheimer to afford a rate taw 

Westheimer has also reviewed the induced oxidations by the Cr(VI)-As(III) couple of iodide, bromide and manganous ions vide supra). The induction factor of 0.5 for Mn(II) implies an intermediate tetravalent chromium species however, the factor of 2 for iodide points to a pentavalent chromium intermediate. Both 

Edwards has also re-examined De Lury s data and finds evidence for an extra term in the rate law, which becomes 

The reaction in 0.2 M acetic acid-0.2 M sodium acetate buffers at an ionic strength of 1.5 M (KNO3) and a temperature of 25 °C, has been reinvestigated recently by Mason and Kowalak . They report the following rate law for a high [As(in)]/[Cr(VI)] ratio 

A second series of experiments was conducted with [Cr(VI)] [As(lII)] and a modified rate law was obtained, viz. 

---

Arsenic(III) (arsenious) acid, H3ASO3.—When arsenic(III) oxide is dissolved in water the corresponding acid is formed ... 

Cm ORINE OXYGEN ACIDS AND SALTS - Cm ORIC ACID AND Cm ORATES] (Vol 5) Arsenious acid anhydride... 

Arsenic Peroxides. Arsenic peroxides have not been isolated however, elemental arsenic, and a great variety of arsenic compounds, have been found to be effective catalysts ia the epoxidation of olefins by aqueous hydrogen peroxide. Transient peroxoarsenic compounds are beheved to be iavolved ia these systems. Compounds that act as effective epoxidation catalysts iaclude arsenic trioxide, arsenic pentoxide, arsenious acid, arsenic acid, arsenic trichloride, arsenic oxychloride, triphenyl arsiae, phenylarsonic acid, and the arsenates of sodium, ammonium, and bismuth (56). To avoid having to dispose of the toxic residues of these reactions, the arsenic can be immobi1i2ed on a polystyrene resia (57). 

Elemental phosphoms from the electrothermal process is a distilled product of high purity and yields phosphoric acid pure enough for most industrial uses without any further treatment. The main impurity is ca 20—100 ppm arsenic present in the phosphoms as the element and in the phosphoric acid as arsenious acid. To remove the arsenic, the phosphoric acid destined for food, pharmaceutical, and some industrial-grade appHcations is treated with excess hydrogen sulfide, filtered, and blown with air to strip out excess H2S. This treatment generally reduces the arsenic content of the phosphoric acid to less than 0.5 ppm. The small amount of filter cake is disposed of in approved chemical landfills. 

The demand for metallic arsenic is limited and thus arsenic is usually marketed in the form of the trioxide, referred to as white arsenic, arsenious oxide, arsenious acid anhydride, and also by the generally accepted misnomer arsenic. 

Chlorate Analysis. Chlorate ion concentration is determined by reaction with a reducing agent. Ferrous sulfate is preferred for quaHty control (111), but other reagents, such as arsenious acid, stannous chloride, and potassium iodide, have also been used (112). When ferrous sulfate is used, a measured excess of the reagent is added to a strong hydrochloric acid solution of the chlorate for reduction, after which the excess ferrous sulfate is titrated with an oxidant, usually potassium permanganate or potassium dichromate. 

Nitrophenylarsonic acid has been prepared by heating p-nitrobenzenediazonium chloride with arsenious acid in hydrochloric acid, by the action of -nitrobenzenediazonium chloride on sodium arsenite, by the action of sodium arsenite on sodium -nitrobenzeneisodiazo oxide, by the diazotization of -nitro-aniline in acetic acid in the presence of arsenic chloride and cuprous chloride, and by the reaction of -nitrobenzenediazonium borofluoride with sodium arsenite in the presence of cuprous chloride. ... 

The solubility of AS2O3 in water, and the species present in solution, depend markedly on pH. In pure water at 25°C the solubility is 2.16 g per lOOg this diminishes in dilute HCl to a minimum of 1.56g per lOOg at about 3 m HCl and then increases, presumably due to the formation of chloro-complexes. In neutral or acid solutions the main species is probably pyramidal As(OH)3, arsenious acid , though this compound has never been isolated either from solution or otherwise (cf. carbonic acid, p. 310). The solubility is much greater in basic solutions and spectroscopic evidence points to... 

Arsenil aure, /, arsenic acid. — unvollkom-mene —, /. arsenious acid,... 

The fact that practically all aromatic amines are readily converted into diazo compounds contributed greatly to Griess s success. The original method (Griess, 1858) by which he diazotized picramic acid (1.1 see Scheme 1-1) consisted of passing nitrous gases, prepared by the reduction of nitric acid with starch or arsenious acid, into an alcoholic solution of the amine. 

To illustrate case a, ii we may refer to the reduction of chlorate by arsenious acid induced by different 1-equivalent oxidizing reagents. The effect of the oxidizing agent is to form arsenic(IV). Chlorate will be reduced by arsenic(IV) which is a stronger reducing agent than arsenic(III). 

It is striking that reactions of arsenic(III) with 1-equivalent oxidizing agents take place fairly slowly, while reactions with 2-equivalent partners e.g. with iodine, are fast. To interpret this behaviour it was suggested by Waters that arsenious acid has the tautomeric forms... 

Guideline 10. Inverse orders arise from rapid equilibria prior to the rate determining step. In order to illustrate this point, consider the oxidation of arsenious acid in an aqueous solution. 

Arsenic peroxides, 13 404 Arsenic removal, in municipal water treatment, 26 124 Arsenic trioxide, 3 264, 265-266 Arsenic vapor, 3 264, 264t Arsenious acid, presence in water and food, 3 276t... 

Among the precipitants employed were tannic acid, tartar emetic, rosin soaps, fatty acid (stearic, oleic) soaps, sulphonated oils (Turkey red oil), earth lakes (mixed natural silicates), phosphates, casein and arsenious acid. The fastness properties of these pigments... 

In iodimetry, quantitative oxidation of reducing agents, such as arsenious acid (H2As03) may be carried out by employing standard solutions of iodine as shown under ... 

Synonyms arsenic oxide arsenic sesquioxide white arsenic arsenic (III) oxide arsenious acid anhydride... 

Yokoyama,T.,Takahashi,Y. Tarutani,T. 1993. Simultaneous determination of arsenic and arsenious acids in geothermal water. Chemical Geology, 103, 103-111. 

By the action of nascent hydrogen upon soluble arsenic compounds, as by the introduction of arsenious acid into on apparatus evolving hydrogen —... 

A monobasic arsenious acid, OHo, conosponding to ni-trous aoid, appears to exist, one of its compounds, AsOAmo, being known. Arsenious aoid when boiled with cupric aco. tato yields SchweinfUrt green, 8A ,0,Cuo", Ou(CjH,OJ,. 

The rate of a reaction is expressed as the increase in the amount of a particular product, or the decrease in the amount of a reactant, per second at a time t. For reactions in a fluid phase, it is usual to substitute concentrations, or for gases partial pressures, for amounts. (See Section 5.6 for treatment of the kinetics of some solid-state reactions.) Note that the numerical value of the rate may depend on how we choose to define it. For example, in the oxidation of aqueous iodide ion by arsenic acid to give triiodide ion and arsenious acid,... 

---