Primary standard arsenic oxide

Antimony(ni) is titrated to antimony(V) in neutral or slightly alkaline solution with iodine to a blue starch end point. The iodine is standardized against primary standard arsenic(in) oxide. Tartaric acid is added to complex the antimony and prevent its hydrolysis to form insoluble basic salts such as SbOCl and Sb02Cl (which form in slightly acid and neutral solution). 

In this connection it must be pointed out that standard samples which have been analysed by a number of skilled analysts are commercially available. These include certain primary standards (sodium oxalate, potassium hydrogenphthalate, arsenic(III) oxide, and benzoic acid) and ores, ceramic materials, irons, steels, steel-making alloys, and non-ferrous alloys. 

Method A With arsenic(III) oxide. This procedure, which utilises arsenic(III) oxide as a primary standard and potassium iodide or potassium iodate as a catalyst for the reaction, is convenient in practice and is a trustworthy method for the standardisation of permanganate solutions. Analytical grade arsenic(III) oxide has a purity of at least 99.8 per cent, and the results by this method agree to within 1 part in 3000 with the sodium oxalate procedure (Method B, below). 

Calculation. It is evident from the equation given above that if the weight of arsenic(III) oxide is divided by the number of millilitres of potassium permanganate solution to which it is equivalent, as found by titration, we have the weight of primary standard equivalent to 1 mL of the permanganate solution. 

A) With arsenic(III) oxide Discussion. As already indicated (Section 10.94), arsenic(III) oxide which has been dried at 105-110 °C for two hours is an excellent primary standard. The reaction between this substance and iodine is a reversible one ... 

Apparent indicator constant 264, 267 Apparent stability constant 59 Aqua regia 111 Arc alternating current, 764 direct current, 763, 771 sensitivities of elements, (T), 766 Aromatic hydrocarbons analysis of binary mixtures, 715 Arsenates, D. of (ti) 357 Arsenic, D. of as silver arsenate, (ti) 357 as trisulphide, (g) 448 by iodine, (am) 634, (ti) 397 by molybdenum blue method, (s) 681 by potassium bromate, (ti) 406 by potassium iodate, (ti) 401 in presence of antimony, (s) 724 Arsenic(III) oxide as primary standard, 261... 

Iodine can be purified by sublimation from potassium iodide and calcium oxide and weighed as a primary standard. Because of the limited solubility and volatility of iodine, it must be dissolved in concentrated potassium iodide solution and diluted to volume. Air oxidation of iodide should be minimized by preparing the solution with water free of heavy-metal ions and storing it in a cool, dark place. Because of the inconvenience of weighing iodine accurately, its solutions are commonly standardized against arsenic(III) oxide (primary standard) or thiosulfate. ... 

Arsenic(III) oxide (AS2O3) is available in pure form and is a useful (and poisonous) primary standard for many oxidizing agents, such as Mn04. AS2O3 is first dissolved in base and titrated with MnOJ in acidic solution. A small amount of iodide (F) or iodate (10J) is used to catalyze the reaction between H3ASO3 and MnO. The reactions are... 

Arsenic trioxide may be made by burning arsenic in air or by the hydrolysis of an arsenic trihaUde. Commercially, it is obtained by roasting arsenopyrite [1303-18-0] FeAsS. It dissolves in water to a slight extent (1.7 g/100 g water at 25°C) to form a weaMy acidic solution which probably contains the species H AsO, orthoarsenous acid [36465-76-6]. The oxide is amphoteric and hence soluble in acids and bases. It is frequendy used as a primary analytical standard in oxidimetry because it is readily attainable in a high state of purity and is quantitatively oxidized by many reagents commonly used in volumetric analysis, eg, dichromate, nitric acid, hypochlorite, and inon(III). 

The CAA establishes national primary and secondary air quality standards for sulfur oxides, particulate matter, carbon monoxide, ozone, nitrogen dioxide, and lead. It also limits the emission of 189 listed hazardous waste pollutants such as vinyl chloride, arsenic, asbestos, and benzene (CAA, 1977). States are responsible for enforcement of the CAA. To assist in this effort. Air Quality Control Regions (AQCRs) were established. Allowable emission limits are determined by the AQCR or its subunit, the Air Quality Management District. These emission limits are based on whether or not the region is currently within attainment of National Air Quality Standards. 

---