Solution Arsenical

Arsenic tniodide (arsenic(III) iodide), Asl, can be precipitated from a hot solution of trivalent arsenic in hydrochloric acid by the addition of potassium iodide, or it can be formed by treating elemental arsenic with a solution of iodine in carbon disulfide. It is not as easily hydrolyzed as the other arsenic haUdes, but it decomposes slowly in air at 100 °C (rapidly at 200°C) to give a mixture of iodine, arsenic trioxide, and elemental arsenic. Solutions of Asl are unstable, particularly in the presence of moisture. 

Arsenic pentasulfide (arsenic(V) sulfide), As S q, is stable in air up to 95°C, but at higher temperatures begins to dissociate into arsenous sulfide and sulfur. It is prepared by the fusion of arsenic with sulfur foUowed by extraction with ammonia and reprecipitation at low temperatures by addition of hydrochloric acid. Arsenic pentasulfide is precipitated at low temperatures from strongly acidic arsenate solutions by a rapid stream of hydrogen sulfide. It is hydrolyzed by boiling with water, yielding arsenous acid and sulfur. Salts derived from a number of thioarsenic acids are formed from arsenic pentasulfide and alkaH metal sulfides. 

Treat the arsenate solution (say, 20.0 mL of ca 0.025M) in a glass-stoppered conical flask with concentrated hydrochloric acid to give a solution in 4M hydrochloric acid. Displace the air by introducing two 0.4 g portions of pure sodium hydrogencarbonate into the flask. Add 1.0 g of pure potassium iodide, replace the stopper, mix the solution, and allow to stand for at least 5 minutes. Titrate the solution, whilst stirring vigorously, with standard 0.1M sodium thiosulphate. 

As an alternative, a reversible indicator may be employed, either (a) 1-naphthoflavone (0.5% solution in ethanol, which gives an orange-coloured solution at the end-point), or (b) p-ethoxychrysoidine (0.1% aqueous solution, colour change pink to pale yellow). Under these conditions, the measured 25 mL portion of the arsenic solution is treated with 10 mL of 10 per cent potassium bromide solution, 6 mL of concentrated hydrochloric acid, 10 mL of water and either 0.5 mL of indicator (a) or two drops of indicator (b). 

Standard arsenic solution. Dissolve 1.320 g arsenic(III) oxide in the minimum volume of 1M sodium hydroxide solution, acidify with dilute hydrochloric acid, and make up to 1 L in a graduated flask 1 mL contains 1 mg of As. A solution containing 0.001 mg As per mL is prepared by dilution. 

Transfer an aliquot portion of the arsenate solution, having a volume of 25 mL and containing not more than 20 jug of arsenic, to the 50 mL Pyrex evolution vessel A shown in Fig. 17.17, and add sufficient concentrated hydrochloric acid to make the total volume present in the solution 5-6 mL, followed by 2 mL of the potassium iodide solution and 0.5 mL of the tin(II) chloride solution. Allow to stand at room temperature for 20-30 minutes to permit the complete reduction of the arsenate. 

Figure 8. Regeneration of ODA-clinoptilolite column loaded with arsenate by means of 2% NaCl aqueous solution and breakthrough curves for ODA-clinoptilolite in arsenate solution of co = 25 mg/L repeated cycle after regeneration, first cycle breakthrough curve on Pb-clinoptilolite (from the left).

Materials Required Arsenic limit test apparatus HgCl2—paper smooth white filter paper (having thickness in mm of 400 paper = weight in g per Sq. M.), soaked in a saturated solution of HgCl2, pressed to get rid of excess of soln. and dried at about 60°C in the dark lead acetate solution 10.0% w/v soln. of PbAc2 in C02 free water KI (AsT), 1.0 g Zn (AsT) 10.0 g Dilute Arsenic solution (AST) Standard stains, Test Solutions—are prepared according to the Indian Pharmacopoeia 1996. 

The test solution prepared as specified, is placed in the wide-mouthed bottle, 1 g of KI (AsT) and 10 g of Zn (AsT) are added, and the prepared glass tube is placed quickly in position. The reaction is allowed to proceed for 40 minutes. The yellow stain that is produced on the HgCl2 paper if As is present is compared by daylight with the standard stains obtained by performing in an identical manner with known quantities of dilute arsenic solution (AsT). The comparison of the stains is made immediately at the completion of the test. 

Power et al. (2005) show the effeet of pH and initial As(III) coneentration on the kineties of arsenite oxidation at bimessite-water interfaees, when a competitive metal (e.g., Zn) is present in an adsorbed or nonadsorbed state (Fig. 16.5). Two well-defined trends in the As(III) oxidation reactions can be distinguished (1) the extent of As(III) oxidation decreases with increasing pH from 4.5 to 6.0 and (2) oxidation on a percent basis is suppressed with increasing initial As(III) concentration from 100 to 300 dM. The pH effects on As(III) oxidation may have been influenced by competitive adsorption reactions between As(III) and reaction products (e.g., Mn(II)) and were not influenced by arsenic solution speciation. The suppressed As(III) oxidation rate constant may be a result of differences in the amount of Mn(II) release, which compete with dissolved As(III) species for unreacted Mn(IV) surface sites, and of Mn(II) adsorption, which inhibit the reaction between As(III) and Mn(IV) surface sites. 

Arsenic(in) and Arsenic(V) Sulphides. Pass a stream of hydrogen sulphide into sodium arsenite and sodium arsenate solutions. What happens Run similar experiments with acidified solutions of the same salts. What do you observe in this case Write the equations of the reactions and explain the occurring phenomena. 

To provide a stock solution for flameless atomic absorption, add 25 ml of HC1 (cone.) and make the volume to approximately 50 ml with water. Add 5 ml 0.125% arsenic solution (5.0 mg) and heat to boiling. Add 8 ml of hypophorous acid (50% ) and boil for 5 min. Cool and filter through two 5fi Teflon millipore filters. Wash with HC1 (1 1) and finally with water. Place millipore funnel and Teflon filters in a 50 ml beaker. Add two 1 ml portions of HN03 down the sides of the millipore funnel. Then heat to complete the dissolution of selenium and arsenic. Rinse off the funnel and millipore filters. Transfer to a 25 ml volumetric flask and add 10 mg. of nickel as Ni(N03)2. Make to volume with water. 

Basic mercuric sulphate is converted into mercuric orthoarsenate and mercuric oxide by warming with sodium mono hydrogen arsenate solution. Hot acetic acid will extract the oxide.5... 

When mercuric oxide is treated with aqueous arsenic acid, the solid phase separates into two layers, one of which is mercuric oxide and the other a basic mercuric arsenate of composition 3Hg0.Hg3(As04)2. When ammonium arsenate solution acts on mercuric oxide, a product of composition Hg2NH2As04 is obtained.6... 

This reaction is quantitative if the iodine is removed by titration with thiosulphate.5 It is necessary to allow the solution to stand for 10 to 15 minutes, preferably in the dark, before completing titration, to ensure completion of the reaction. During titration the high acid concentration may cause decomposition of the thiosulphate the solution is therefore diluted. The above reaction, however, is reversible, and considerable dilution will cause reversal, leading to low results satisfactory results are obtained6 when the solution is about 4N with respect to hydrochloric acid and contains about 1 per cent, of potassium iodide. The titration should be made at the ordinary temperature and starch indicator may or may not be used. The addition of sodium chloride to the arsenate solution has been advocated.7 When only very small quantities of arsenic are being determined, an atmosphere of carbon dioxide is essential for accurate results, as iodine is liberated by the action of air on strongly acid iodide solutions.8... 

Calcium Arsenate. CAS 7778-44-11. Ca,tAs04) . white precipitate, formed by reaction of soluble calcium salt solution and sodium arsenate solution. pK,p = 18.17. 

PEARSON S SOLUTION. A dilute sodium arsenate solution containing 0,1% anhydrous sodium arsenate. 

To avoid problems previously encountered with flame atomic absorption spectrometry of arsenic, and also with flameless methods such as that in which the dementis converted to arsine, Ohta and Suzuki [25] proposed an alternative method based on electrothermal ionisation with a metal microtube atomiser. Effective atomisation can be achieved by the addition of thiourea to the arsenic solution or by preliminary extraction of the arsenic-thionalide complex. The second method is recommended for soil samples so as to avoid interference due to the presence of trace elements. 

The following arsenate (AsO -) adsorption data was obtained by adding 20.42 g of kaolinite to 200 mL of arsenate solution, ... 

Arsenic Determine as directed under Arsenic Limit Test, Appendix IIIB, using a Sample Solution prepared as directed for organic compounds, and 1.0 mL of the Standard Arsenic Solution (1 g As) in the control. 

Arsenic Determine as directed under Arsenic Limit Test, Appendix IIIB, using a Sample Solution prepared as directed for organic compounds, and 4 g of sample, accurately weighed. The absorbance caused by any red color from the solution of the sample does not exceed that produced by 2.0 mL of Standard Arsenic Solution (2 gig As) when treated in the same manner and under the same conditions as the sample. Color (AOCS-Wesson) Determine as directed under Color (AOCS-Wesson), Appendix VII. 

Standard Solution Prepare this solution in the same manner as the Sample Solution, but use 6.0 mL of Standard Arsenic Solution (see Arsenic Limit Test, Appendix IIIB) in place of the sample. 

Refer to the Arsenic Limit Test, Appendix IIIB. Add 2 mL of potassium iodide TS and 0.5 mL of Stannous Chloride Solution to the Erlenmeyer flask, and continue as directed in the Procedure, beginning with, Allow the mixture to stand for 30 min at room temperature. .. but use 6.0 mL, rather than 3.0 mL, of Standard Arsenic Solution in the preparation of the standard. 

Standard Arsenic Solution Accurately weigh 132.0 mg of arsenic trioxide that has been previously dried at 105° for 1 h, and dissolve it in 5 mL of a 1 5 sodium hydroxide solution. Neutralize the solution with 2 N sulfuric acid, add 10 mL in excess, and dilute to 1000.0 mL with recently boiled water. Transfer 10.0 mL of this solution into a 1000-mL volumetric flask, add 10 mL of 2 N sulfuric acid, dilute to volume with recently boiled water, and mix. Use this final solution, which contains 1 pig of arsenic in each milliliter, within 3 days. 

Colorimetric Assay for Arsenic in Blood Standard Arsenic Solutions. Dissolve 2.4196 g of arsenic trichloride in sufficient M hydrochloric acid to produce 1000 ml. This solution contains 1 mg of As in 1 ml. Serially dilute the solution with water to produce solutions containing 0.5, 2.0, 5.0, and... 

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