Estimation Of Metals As Sulphides : Estimation of rhenium. silver and mercury

1. It has been shown that under proper conditions rhenium, mercury and silver can be precipitated quantitatively as pure sulphides and the precipitate weighed directly for the estimation of the metal. 2. in the case of rhenium the solution containing perrhenate is treated with excess of alkali sulphide and the resulting solution containing the thiohalt is treated with excess of concentrated hydrochloric acid and ammonium sulphate. The precipitate is weighed directly as Re₂S₇. 3. In the case of silver the metal in ammoniacal solution is treated with excess of alkali sulphide and the precipitate weighed directly as Ag₂S. 4. In the case of mercury, the solution containing the metal is treated with excess of alkali sulphide solution in the cold followed by excess of hydrochloric acid. The precipitate obtained under these conditions is completely free from sulphuur and can be weighed directly as HgS. 5. Although germanium forms a thiosalt which decomposes with excess of hydrochloric acid, it was found that the metal cannot be estimated as sulphide owing to the pephization of the precipitate on washing and its decomposition on heating.     

Oxidations with potassium permanganate in the presence of fluoride

Summary Quadrivalent selenium can be determined with fair accuracy by mixing with an excess of KMnO₄ in the presence of 25–75 ml of 2% NaF solution and 4–7 ml of 9 N sulfuric acid. After leaving the reaction mixture for 10–30 minutes the excess KMnO₄ is estimated by one of the following procedures: A) Titration of the excess KMnO₄ with monovalent mercury, B) Adding an excess of Hg₂ ²⁺ solution to react with the excess KMnO₄ followed by titrating the excess mercurous with KMnO₄ solution.Part I: Issa, I. M., and M. Hamdy, Z. analyt. Chem. 172, 94 (1980).     

A wet chemical method for the estimation of carbon in uranium carbides

A wet chemical method for the estimation of carbon in uranium carbides has been developed, based on oxidation with a saturated solution of sodium dichromate in 9M sulphuric acid, absorption of the evolved carbon dioxide in a known excess of barium hydroxide solution, and titration of the excess of barium hydroxide with standard potassium hydrogen phthalate solution. The carbon content obtained is in good agreement with that obtained by combustion and titration.     

溶剂化的热力学集团展开理论

把二元溶液的过剩内能（excess energy）分成溶剂-溶剂、溶剂-溶质及溶质-溶质相互作用部分。利用集团展开方法给出了二元溶液在正则系综的配分函数的表达式,利用该表达式得到了溶质的偏摩尔内能(partial molar energy)和偏摩尔熵(partial molar entropy)的表达式。在无限稀溶液情形,过剩偏摩尔内能的溶剂-溶剂部分又称重组织内能（reorganization energy）,它反映了溶质存在时对其周围溶剂分子之间的相互作用能的影响。研究表明,在溶质的粒子数密度相对较大时,溶质分子之间的相互作用将影响过剩偏摩尔内能的溶剂-溶剂部分,对于稀溶液,过剩偏摩尔内能的溶剂-溶剂部分与溶质的摩尔分数成线性关系。对低密度二元溶液,溶质的过剩偏摩尔内能和过剩偏摩尔熵也与溶质的摩尔分数成线性关系。     

Excess Gibbs Energy of Mixing for Organic Carbonates from Fitting of Their Binary Phase Diagrams with Nonideal Solution Models

The excess Gibbs energies of mixing in the liquid state were evaluated for all the ten binary combinations of these five organic carbonates: ethylene carbonate (EC), propylene carbonate, dimethyl carbonate (DMC), ethyl methyl carbonate, and diethyl carbonate by fitting their measured binary phase diagrams with thermodynamic nonideal solution models based on the regular solution model. Using the results of these model fits, activity coefficients of the components in the solvent mixtures were calculated for the binary series containing EC and DMC as the common component, and the composition-averaged excess Gibbs energies of mixing were calculated by integrating the energy in the whole composition range for all the binaries. The results showed the excess Gibbs energy of mixing, and therefore the intermolecular forces, to be responsible for the changes in the phase diagrams, in the activity coefficients, and in the composition-averaged excess energy for the different binary solution combinations.     

Determination of amides

A method has been developed for the quantitative determination of amides. The compound is saponified with a large excess of alkali and the resulting solution passed through a heated cationexchange resin in the hydrogen form. The resin neutralizes the excess sodium hydroxide and converts the carboxylic salt to the free acid which is then titrated directly in the effluent with standard alkaline solution. The time required for a determination is less than one hour.     

Contributions to the basic problems of complexometry-XXV Determination of rare earths and phosphate without separation

A new method for coraplexometric determination of rare earths (RE) and phosphate without prior separation is described. It is based on indirect determination of RE by back-titration of an excess of DTPA with zinc solution, with Xylenol Orange as indicator. After the titration an excess of La-EDTA complex solution is added and the solution is titrated again with zinc at 40-50 degrees . During this titration lanthanum is displaced from its complex and precipitated as phosphate: LaY(-) + Zn(2+)+ PO(4)(3-) = LaPO(4) + ZnY(2-). The consumption of zinc solution corresponds to the amount of phosphate.     

Quantitative determination of olefin oxide, chlorohydrin, and cyclocarbonate in the presence of each other

A procedure was developed for the quantitative determination of olefin oxide, chlorohydrin, and cyclocarbonate simultaneously present in the reaction mixture of the synthesis of cyclocarbonate from olefin oxide and CO₂. To determine olefin oxide, an acetone solution of hydrochloric acid was added to a portion of the reaction mixture, and the excess of hydrochloric acid was titrated with an aqueous solution of potassium hydroxide with visual detection. The concentrations of chlorohydrin and cyclocarbonate were calculated from the data of the potentiometric titration of the same solution to which excess potassium hydroxide was added. Deceased.     

Dosage rapide du chrome et du vanadium

The two elements are supposed to be in solution in their maximum value. The total chromium + vanadium content is determined by direct titration in 23̄ 3 N sulphuric acid solution with a ferrous solution in the presence of sulphonated diphenyl amine as an oxydo-reduction indicator. Vanadium is titrated in the same solution after bringing it into its highest valence state by means of a slight excess of permanganate. After the destruction of the excess of oxidizing agent with sodium azide, the titration is completed with the ferrous solution in the presence of the same indicator.     

A rapid complexometric scheme for analysis of iron, aluminium, calcium and magnesium in slags

A simple and rapid complexometric method has been developed for the simultaneous determination of iron, aluminium, calcium and magnesium in a single solution in slags. Phosphorous and small amounts of chromium (1.5 mg) and vanadium (1 mg) do not interfere in the titration. Titanium and manganese are suitably masked with lactic acid and tetra sodium pyrophosphate, respectively. In a suitable aliquot, iron is titrated at pH 2 with EDTA, using sulphosalicylic acid as indicator. To this solution, excess disodium 1,2-cyclohexane diamine tetra acetic acid (DCTA) is added and aluminium is titrated by titrating the excess DCTA with standard copper sulphate solution at pH 3.5, using 1-(2-pyridylazo)-2-naphthol (PAN) as an indicator. A known excess of EDTA is added, the pH is raised to 10 and calcium and magnesium are jointly titrated by titrating the excess EDTA with copper sulphate solution, using PAN indicator. The Ca-EDTA complex is demasked with ammonium oxalate at pH 5 and the released EDTA equivalent to calcium is titrated with copper sulphate solution at pH 10 with PAN indicator. Results of analysis compare favourably with certified values and values obtained by standard methods for BCS and other slags. A set of five samples can be analysed for iron, aluminium, calcium and magnesium in four hours as compared to three days by the classical conventional method.     

Thermochemical investigations of nearly ideal binary solvents. I. Standard heats and volume changes of solution in methanol-isopropanol mixtures at 25°C

Standard heats and volume changes of solution of acetone,n-butanol, chloroform, and water in methanol, isopropanol, and mixtures of the two are reported. In every case, the value of a measured property in a mixture is more negative than the mole-fraction average of the values measured in the pure solvents. Equations relating the heat of solution in a binary mixture to the heats of solution in the pure solvents and the excess enthalpy of the binary mixture are developed from equations for the excess enthalpy of simple ternary systems. Heats of solution ofn-butanol agree fairly well with predicted values. Combination of standard heats of solution with standard volume changes of solution allow estimation of standard energy changes of solution at constant volume.     

Potentiometric determination of plutonium by argentic oxidation, ferrous reduction and dichromate titration

A simple and rapid method is described for the routine determination of plutonium with a coefficient of variation of better than 0.2%. It is directly applicable to nitrate solutions containing a large amount of uranium; moderate amounts of iron, molybdenum, fluoride and phosphate do not interfere. Chromium, cerium and manganese interfere quantitatively, and the procedure may also prove convenient for the determination of these elements. The plutonium is oxidised to the sexivalent state with argentic oxide in nitric acid solution, and the excess of oxidant is destroyed by reaction with sulphamic acid. A weighed small excess of iron(II) solution is then added, and the excess is titrated potentiometrically with standard potassium dichromate solution using polarised gold indicator electrodes. The whole determination is performed in one vessel at room temperature, and takes about 20 min.     

A revised quantum chemistry-based potential for poly(ethylene oxide) and its oligomers in aqueous solution

We have conducted a high-level quantum chemistry study of the interactions of 1,2-dimethoxyethane (DME) with water for complexes representing both hydrophilic and hydrophobic hydration. It was found that our previous quantum chemistry-based force field for poly(ethylene oxide) (PEO) and its oligomers in aqueous solution did a poor job in describing the hydrophobic binding of water to the ether, consistent with our recent calculations of the excess free energy and entropy of hydration of DME. Our original force field was revised to more accurately reproduce the interaction of water with the carboneous portions of DME. Molecular dynamics simulations of aqueous DME solutions using the revised quantum chemistry-based potential yielded good agreement with experiment for excess free energy, enthalpy, and volume as well as excess solution viscosity and the self-diffusion of water. Comparison with our original potential revealed that the relatively hydrophobic ether-water interactions in the new potential strongly reduced the favorable excess free energy and enthalpy but have relatively little influence on the excess entropy for dilute DME solutions. Other properties of DME and PEO solutions including conformational populations and dynamics, solution viscosity, hydrogen bonding, water translational and rotational diffusion and neutron structure factor as a function of solution composition were found to be largely unchanged from those obtained using the original potential.     

Differential titrimetric determination of mixtures of selenium and tellurium

Methods are described for the differential titrimetric determination at room temperature of mixtures of selenium(IV) and tellurium(IV). The test solution in 0.75-3.5M condensed phosphoric acid medium is oxidized with an excess of permanganate and the unreacted permanganate is titrated with iron(n), with ferroin as indicator, to indicate the total content of selenium and tellurium present. Then 10-20 ml of 10M sulphuric acid, 0.4 ml of 0.1% osmium tetroxide solution and an excess of arsenic(III) are added to the same solution and the unreacted arsenic(III) is titrated with permanganate (ferroin as indicator) to indicate the content of tellurium.     

Oxidation of sulphides with alkaline potassium permanganate

Summary Sulphides are oxidised with potassium permanganate in alkaline medium to give dithionate. A method based upon this reaction is proposed for the determination of sulphides. The method consists in mixing the sulphide solution with an excess of permanganate in presence 1–2 M NaOH and 0.2 g telluric acid. The excess permanganate is then treated with ferrous ammonium sulphate in acid medium and the excess ferrous titrated with permanganate.     

Potentiometric argentimetric method for the successive titration of sulphide and dissolved sulphur in polysulphide solutions

Sulphide sulphur and dissolved sulphur in a polysulphide solution can be successively determined with satisfactory accuracy and reproducibility by potentiometric argentimetry in which a sulphide-selective indicator electrode is used. Before the titration, polysulphide ions need to be converted by an excess of potassium cyanide into thiocyanate and sulphide ions. The excess of cyanide ions is masked with formaldehyde and sulphuric acid, then the solution is made alkaline with ammonia and titrated with silver nitrate till the first end-point is reached (sulphide sulphur). After the acidification of the solution with sulphuric acid, the titration is continued till the second end-point is attained (dissolved sulphur).     

Direct complexometric determination of aluminium in "alzinoy"

A simple and precise method for the complexometric determination of aluminium in "Alzinoy" (a binary alloy of aluminium and zinc) is described. After dissolution of the sample in hydrochloric acid, aluminium, zinc and any lead and iron are complexed with excess of EDTA. The excess of EDTA is titrated with lead solution, with Xylenol Orange as indicator. Ammonium fluoride is then added to decompose the Al-EDTA complex, and the EDTA liberated is titrated with lead solution. Four samples can be analysed in about 45 min.     

Redox reactions in nonaqueous media : Determination of organoisothiocyanates and organoisocyanates

A simple and accurate method has been developed for the determination of organoisothiocyanates and organoisocyanates based on their quantitative reaction with n-butylamine in dimethylformamide medium to form substituted thioureas and ureas, respectively. The solution is mixed with 6 to 7 times its volume of acetonitrile and an excess of carbon disulphide, which converts the residual amine quantitatively into the corresponding n-butylammonium n-butyl dithiocarbamate. The determination is completed by titrating the resulting dithiocarbamate with iodine monobromide solution in acetonitrile. The end point is detected visually by the yellow color imparted to the solution by the first drop of oxidant solution in excess. The dithiocarbamates are quantitatively oxidized to the corresponding thiuram disulphides.     

Pollution-free method for the determination of iron in iron ore

A method for the determination of total iron in iron ores and concentrates is described which avoids the use of mercuric chloride. The sample is decomposed either by an acid attack or by fusion with sodium peroxide. The hot sample solution in about 6M hydrochloric acid is treated with hot 10% stannous chloride solution till pale yellow, followed by addition of a slight excess of 2% titanous chloride solution; the excess is then oxidized with perchloric acid (1 + 1). The solution is rapidly cooled in ice-water, and the iron (II) is titrated with potassium dichromate (sodium diphenylsulphonate as indicator). The results show the same degree of precision, accuracy, and degree of interference as those obtained by the standard stannous chloride-mercuric chloride method.     

Determination of mixtures containing amines and thioureas

A convenient and accurate method has been described for the analysis, on the same sample solution, of mixture of amines and thioureas. The mixture solution is first analyzed for amines by an acidimetric titration. The titrated solution is acidified with more aqueous acid and then analyzed for thioureas by an oxidimetric titration. The method has been successfully applied to the analysis, also on the same sample solution, of mixtures containing isocyanates and thioureas. A known excess of standard n-butylamine added to the mixture solution in diemthylformamide converts the isocyanates to the corresponding disubstituted ureas. Acidimetric titration of the excess of amine followed by iodatometric titration of thiourea present enable the mixture to be analyzed for both the components. The methods described are reliable and have wide applications.