Mercurous nitrate as a reductimetric reagent : The interference of the more common cations and anions in the determination of iron

The interfering effect of most of the more common cations and anions on the titration of ferric iron with mercurous nitrate has been examined. As would be expected, ions capable of oxidising ferrous iron interfere. Certain other cations and anions interfere, but in several cases this effect can be eliminated. Copper and thallium must be completely absent, and ions which give coloured products with thiocyanate ions, e.g., molybdenum.     

Mercurous nitrate as a reductimetric reagent: The potentiometric titration of ferric iron in the presence of ions forming highly coloured thiocyanates

The reduction of ferric iron by means of mercurous salts in the presence of an excebs of ammonium, thiocyanate can be predicted on theoretical grounds. By consideration of the oxidation potentials involved it has been shown by calculation that quantitative reduction of the ferric iron is to be expected.—The titration may be effected potentiometrically using a bright platinum indicator electrode in conjunction with a silver/silver chloride electrode or a saturated calomel reference electrode. Ferric iron can be titrated in the presence of ions such as cobalt which form intensely coloured thiocyanate complexes.A possible method for the titration of molybdate by means of mercurous nitrate has been examined. The sensitivity of the method suffers from the instability of potential of the system under titration, but particularly since tungstate does not interfere, the method is worthy of further study.     

Mercurous nitrate as a reductimetric reagent : The determination of copper

It has been found that in the presence of excess thiocyanate ions, cupric copper will oxidise ferrous ions. Use has been made of this reaction to determine copper by titration of the ferric iron produced, with mercurous nitrate. Although this reaction is the reverse of that usually observed, where the cuprous ion reduces the ferric iron, it has been found that the large excess of thiocyanate is responsible for this effect.     

Mercurous nitrate as a reductimetric reagent : The titration of various oxidising agents

It has been found that when excess of a solution containing ferrous ions is added to certain oxidising agents, the equivalent amount of ferric iron produced can be titrated accurately with mercurous nitrate, enabling the original oxidant to be assessed. Oxidising agents which have been determined in this way are potassium permanganate, potassium persulphate, ceric sulphate, sodium vanadate, potassium chlorate, hydrogen peroxide and potassium dichromate. The last substance provides a convenient primary standard for the standardisation of mercurous nitrate solutions.     

Determination of chromate and cyanide by anion-exchange with lead iodate, and the analysis of mixtures of cyanide, thiocyanate and halides

Chromate and cyanide have been determined by their ability to displace iodate from sparingly soluble lead iodate. The released iodate is treated with acidified iodide to give iodine, which is determined either by titration with thiosulphate, or spectrophotometrically as its blue complex with starch. Chromium(III) has been determined as chromate after its oxidation with peroxydisulphate. Sulphate, iodide, bromide, chloride, fluoride, oxalate, tartrate, phosphate and thiocyanate do not interfere. Thiosulphate, sulphite, sulphide, hexacyanoferrate(II) and molybdate ions vitiate the results. Silver, mercury, barium and iron(III) should be masked. Mixtures of cyanide, thiocyanate and halides have been analysed by using complementary procedures that employ the iodates of lead and mercury, and bromine oxidimetry. It has been shown that cyanide or thiocyanate interferes in the determination of iodide by oxidation to iodic acid, because of formation of cyanogen bromide.     

5-Methyl-7-nitroso-8-hydroxyquinoline and its sensitivity and selectivity towards certain metallic ions

5-Methyl-7-nitroso-8-hydroxyquinoline (5-methyl-7-nitroso-oxine), hitherto undescribed, has been prepared and tested for its sensitivity and selectivity towards various metallic ions at differing pH's. The metals tested include cadmium, ferrous and ferric iron, mercurous and mercuric mercury, lead, nickel, cobalt, thallous thallium, cerous and cerie cerium, copper, chromium, aluminium, zinc, magnesium, vanadium (as vanadate) and gallium. This reagent is comparatively “unsclective” in that it chelates with all the above metals under the conditions employed, and therefore closely follows the behaviour of the parent compound, 8-hydroxyquinoline (oxine). Its average sensitivity is somewhat greater than that of the parent compound, and it shows its greatest sensitivity with. divalent mercury.     

Mercurous nitrate as a reductimetric reagent : The determination of mercurous mercury

Mercurous mercury can be determined indirectly by allowing the test solution to react with an excess of standard ferric alum and back-titrating the unconsumed ferric iron with standard mercurous nitrate. The titration can be carried out in the presence of appreciable quantities of mercuric mercury.     

Potassium meta-periodate as volumetric reagent : Iodine bromide method

Potassium meta-periodate has been used as an oxidising agent in acid medium for the volumetric estimationss of potassium iodide, arsenious oxide, antimonous oxide, stannous chloride, mercurous chloride, sodium sulphite, sodium thiosulphate, sodium tetrathionate, ferrous sulphate, potassium thiocyanate, hydrazine sulphate, phenylhydrazine hydrochloride and hydroquinone by the iodine bromide method. Carbon tetrachloride is used as an indicator. It is coloured pink during the titration. and becomes colourless at the end-point due to the formation of stable iodine bromide complex IBr2-, which does not dissociate, in the presence of a large excess of bromide ion.     

Studies on the adsorption behaviour of trace amounts of cerium on manganese dioxide from aqueous solutions in the presence of complexing agents

Adsorption behaviour of trace amounts of cerium on manganese dioxide has been studied as a function of pH (1–10) in the presence of EDTA, oxalate, citrate, tartrate, cyanide and thiocyanate ions. The influence of their concentration on the adsorption has also been investigated. Maximum adsorption of cerium has been noticed at pH6. Under specific conditions, adsorption of other metal ions has been measured for comparison. Low distribution coefficients are obtained for Cs(I) and Hg(II) in the presence of oxalate, and for Cr(III) in the presence of thiocyanate ions. Based on these data, separation of cesium, chromium and mercury from rare earths and cerium scavenging in natural water or in waste water treatment can be achieved.     

Influence of cyanide and sulphide ions on the reduction and reoxidation of cobalt(II) in thiocyanate solution at mercury electrodes

The process of reduction and reoxidation of cobalt(II) in thiocyanate solution at hanging mercury drop electrode has been investigated by cyclic voltammetric, chronoamperometric and anodic stripping methods. In 0.1 M NaSCN and 0.4 M NaClO₄ solution containing 1×10^?3M cobalt(II), the voltammogram on the first cycle at 0.05 V s^?1 gives a cathodic peak at ?1.06 V with hysteresis on reversal, and an anodic wave with a peak potential of ?0.28 V and with two shoulders near ?0.38 and ?0.45 V, respectively. Multicyclic voltammograms under the same conditions give a cathodic peak at ?0.90 V and an anodic peak at ?0.45 V. The reduction and reoxidation of cobalt(II) in thiocyanate solution is accelerated by the reduction products of thiocyanate ion, cyanide and sulphide ions, which are produced during the electroreduction of cobalt(II).A mechanism of reduction and reoxidation of cobalt(II) which involves a chemical reduction of thiocyanate ion by electroreduced metallic cobalt and takes into account cyanide and sulphide ions is proposed. The hysteresis on the cathodic wave is caused by the difference in reduction potentials of cobalt(II)-thiocyanate and-cyanide complexes. Cyclic voltammetric study of cobalt(II) in perchlorate solution containing trace amounts of cyanide and sulphide ions supports these conclusions.     

Mechanism of electroreduction of cobalt(II) in thiocyanate solutions at mercury electrodes

The process of electroreduction of cobalt(II) in thiocyanate solutions at mercury electrodes has been investigated by cyclic voltammetric, chronoamperometric and polarographic methods. The influences of pH, the concentrations of Co(II) and SCN^?, and the reduction products of SCN^?, CN^? and S^2? on the reduction waves are described. The polarographic pre-wave is an autocatalytic in nature. A mechanism involving an initial reduction of Co(II)—SCN^? at a mercury electrode followed by the chemical reduction of thiocyanate ion with the electroreduced metallic cobalt, and taking into account cyanide, sulfide, and hydroxide ions, the latter being produced by the hydrolysis of cyanide ion, is presented. Cobalt sulfide adsorbed at the electrode surface stimulates further reduction of Co(II)—CN^? and —SCN^? complexes, and depresses the interfering influence of Co(OH)₂, which is reductively desorbed from the electrode surface with giving rise to an additional peak near ?1.08 V vs. SCE.     

Adsorption studies of mercury on zirconium oxide from aqueous solution

The adsorption of mercury on zirconium oxide from aqueous solution has been studied in relation to concentration of adsorbent and adsorbate. The influence of contact time, buffer composition, pH, and foreign ions was also investigated. Thiosulfate, iodide, thiocyanate, EDTA, cyanide and Li(I) drastically reduced adsorption. Adsorption of other metal ions under the same conditions was also investigated. Based on these data, separation of mercury from antimony and neodymium can be achieved.     

Sodium meta-vanadate as volumetric reagent : Iodine monochloride method

Sodium meta-vanadate has been used as an oxidising agent in hydrochloric acid medium for the volumetric estimations of potassium iodide, sodium arsenite, mercurous chloride, potassium thiocyanate, sodium sulphite, sodium bisulphite, sodium thiosulphate, ferrous sulphate and hydrazine sulphate, using iodine monochloride as a catalyst and preoxidiser. Chloroform is used as an indicator. It is coloured pink due to the liberation, of iodine during the titration and becomes light pale yellow at the end-point due to the formation of iodine monochloride.     

Oxidations with potassium permanganate in the presence of fluoride

Summary The titration of ferrous iron in presence of fluoride ions in acid medium gives fleeting end points and erroneous results. A method is deviced to overcome this difficulty by oxidising the ferrous with an excess of KMnO₄ in alkaline medium. After mixing the reactants the excess of KMnO₄ is reduced by an excess of Hg₂ ²⁺ ions in presence of H₂SO₄ and fluoride. The remaining mercurous is then titrated with standard KMnO₄ solution.Part III: Issa, I. M., and M. Hamdy: Z. analyt. Chem. 174, 418 (1960).     

Indirect spectrophotometric determination of chloride by solvent extraction as tris(1,10-phenanthroline)iron(II) thiocyanate

An indirect spectrophotometric method for the determination of small amounts of chloride in fresh waters is described. Chloride ions react with mercury(II) thiocyanate to liberate thiocyanate ions, which can be selectively extracted into nitrobenzene with tris(1,10-phenanthroline)iron(II) chelate cations. The red color (516 nm) of the organic phase measured against a reagent blank is proportional to the initial concentration of chloride ions in the aqueous phase. At least an equimolar amount of tris(1,10-phenanthroline)iron(II) chelate and a 3-fold amount of mercury(II) thiocyanate are needed; the optimal pH range is 1.5–3.5. Beer's law is obeyed over the concentration range of 0.8–5.6 10^-5 M of chloride. The color stability and the apparent sensitivity are better than those of the mercury(II) thiocyanate-iron(III) method. Large amounts of sulphate, phosphate, fluoride, carbonate, acetate, potassium, sodium, and ammonium ions had negligible or no effect ; bromide, iodide, cyanide, sulphide, and thiocyanate interfere.     

Indirect spectrophotometric determination of thiocyanate by extraction as bisthiocyanatobisquinolinemercury(II) complex and its ligand substitution reaction with dithizone

Thiocyanate forms with mercury(II) in the presence of quinoline a mixed-ligand mercury(II) complex, bisthiocyanatobisquinolinemercury(II), and is extracted into chloroform. This mixed-ligand complex is treated with dithizone and forms the bisdithizonatomercury(II) complex. Maximum and constant absorbance of the dithizone complex is obtained when thiocyanate is extracted at pH 5.1-6.5, and Beer's law is obeyed at 498 nm, where the difference in absorbance between the dithizone complex and dithizone is largest. Chloride, bromide, iodide, cyanide and large amounts of ammonium and copper(II) ions interfere.     

Current Efficiency and Electrogravimetric Determination of the Number of Electrons Involved in Galvanostatic Coulometry of Mercury Metal

Abstract

The efficiency of current during the oxidation of mercury metal by galvanostatic coulometry was total in the presence of thiosulphate. The electrogravimetric determination of the number of electrons involved in the oxidation of metallic mercury in the presence of substances which have a great affinity for mercury ions, showed that n=2 in the electrochemical step. On the other hand, the mass variation was not a good method to determine n in the absence of complexing agent due to a coupled chemical process.     

Complex citrates of metals in Inorganic Analysis : Some preliminary observations and the application of citrate complex formation in the qualitative analysis of the metallic ions of the Silver group

The use of sodium citrate as a reagent for the separation of silver group metals has been described. Silver, lead and mercurous ions are all capable of forming soluble citrate complexes, but they differ in their stability. The lead complex is not decomposed by soluble chlorides, whereas silver and mercurous complexes yield the insoluble chlorides. The fact that lead sulphate is soluble in a hot solution of sodium citrate has been utilized for the detection of lead, when present as insoluble sulphate, in a mixture.     

Reduction of methylene blue by thiocyanate: kinetic and thermodynamic aspects

This article reports the reduction of methylene blue (MB) by thiocyanate ions (SCN(-)) in aqueous and micellar solutions. Thiocyanate ions are found to be an effective reducing agent for the decolorization of methylene blue under ambient condition. Effects of salting-in and salting-out agents have been investigated for real-time application in the reduction process. The salting-in agent urea has been found to uniquely enhance the rate of the reduction of MB by thiocyanate ion in the presence of micelles. Again, the catalytic activity of nanoparticles in the reduction of MB has also been studied. Detailed kinetic and thermodynamic aspects have been considered to realize the interaction between methylene blue and thiocyanate. Kinetic studies revealed that the reaction is reversible and follows first-order reaction kinetics.     

Some notes on the reaction between ferric and thiocyanate ions

A spectrophotometric study has been made of the reaction between ferric and thiocyanate ions in sulphuric acid solution. The effects of acidity, thiocyanate concentration, persulphate concentration, temperature, light and added beryllium sulphate upon the stability and colour intensity of the solution are described.For analytical applications in the absence of added sulphate ions the best results are obtained at an acid normality of 1.5 to 2.0, while in the presence of beryllium sulphate at molar concentration it is desirable to increase the acid normality to 3.0. Precise control of thiocyanate concentration and temperature is required. The solutions obey Beer's law and an ultimate sensitivity of 0.035 p.p.m. of Fe is obtained when using a I cm cell.