Oxidations with alkaline permanganate using monovalent thallium for the back titration: Estimation of hydrazine

Oxidation of liydrazine in alkaline solutions with KmnO₄, gives inaccurate results both in the presence of absence of telluric acid. The titration curve is characterized by two inflections.Titration of KmnO₄ with hydrazine gives good results in the presence of Ba⁺² ions and 0.75–1NNaOH (when MnO₄^- gives MnO₂^-) or in the presence of 0.5–2.5N NaOH only (when MnO₄ gives MnO₂).Hydrazine could be estimated by oxidation with KMn0₄ either in the presence of Ba⁺² ions or telluric acid, after which the excess permanganate is back titrated with monovalent thallium. The alkalinity is Kept at 1N NaOH.     

Oxidations with alkaline permanganate using monovalent thallium for the back-titration: Estimation of trivalent arsenic

In absence of Ba⁺² ions arsenite reduces KMnO₄ in alkaline medium to MnO₂ without the appearance of an inflection at the manganate state. Reduction could be checked at the manganate in presence of 1N NaOH and Ba⁺² equal to 3 times that equivalent to MnO₄^-2 and arsenate, and when dilute arsenite solutions are applied viz.0.02N In absence of Ba⁺² ions the end-points are attained later than the MnO₂ stage except in 2–3N NaOH. In presence of telluric acid good results are obtained at all alkalinities whence reduction is checked at Mn⁺⁴.As⁺³ could be estimated also by mixing with KMnO₄ either in the presence of Ba⁺² ions + 1N NaOH or in absence of Ba⁺² ions + I.5–3N NaOH and back-titrating the excess oxidant with monovalent thallium.     

Oxidations with alkaline permanganate using monovalent thallium for the back-titration: Determination of iodate,iodide and ferrocyanide

Iodate, iodide, iodine and ferrocyanide can be estimated by oxidation with KmnO₄ in alkaline media; the excess is back-titrated with TI⁷. I^- and I₂ are oxidized to IO₄^- in the presence of Ba⁺² ions but only to IO₃^- in absence of such ions. The direct titration of IO₃^-, I^- with KmnO₄ proved valueless.Ferrocyanide is oxidized by KmnO₄ in alkaline solutions and MnO₂ is formed. In the presence of telluric acid and 0.025–0.1 N NaOH satisfactory results are obtained. Reduction of MnO₄^- with ferrocyanide gives MnO₄^-2 and the results are variable, depending on the rate of adding the ferrocyanide.     

Oxidations with alkaline permanganate using monovalent thallium for the back titration: Estimation of lead. selenium,tellurium and chromium

Monovalent-thallium can be successfully used for the back titration of KMnO₄ in the course of estimating Pb⁺², Sc⁺⁴, Te⁺⁴ and Cr⁺³.Reduction of KMnO4 with Tl+ in alkaline solution yields MnO₄^-2 which then passes to MnO₂. he end-points are attained late, but in presence of telluric acid the end-point at MnO₂ stage corresonds to the theoretical value. Reduction at the MnO₄^-2 stage can be checked in presence of Ba⁺² ns and good results obtained with 1–1.5N NaOH.     

Quadrivalent uranium as a reducing agent in potentiometric titrations: Estimation of dichromate,permanganate, bromate and tellurate

Quadrivalent uranium can further be used for the estimation of K₂Cr₂O₇ KmnO₄ (in acid or alkali), H₂TeO₄ and KbrO₃ either alone or in conjunction with Fe⁺³, Ce⁺⁴ and V⁺⁵ The reaction proceeds rapidly in dilute acid solutions and especially when Fe⁺³ iron is used as a catalyst. Reduction of aqueous KmnO₄ gives MnO₂ which then dissolves in the acid of the reagent and undergoes reduction to Mn⁺². In acid solutions no MnO₂ separates. In alkaline medium (1.5–3N NaOH) KmnO₄ is reduced absolutely to MnO₂.     

Oxidations with alkaline permanganate using monovalent thallium for the back titration: Estimation of hydrogen peroxide

Owing to the instability of hydrogen peroxide in alkaline solutions, direct oxidation with KmnO₄ did not yield accurate results.The back titration of KmnO₄ in the presence of IN NaOH and Ba⁺² ions also gave inaccurate results. The reaction could not be checked at the manganate state. However, in the presence of 2N NaOH and telluric acid quantitative data were obtained, which is not the case if telluric acid is absent.Another advantageous method is the oxidation of hydrogen peroxide with excess KmnO₄ in the presence of 1N NaOH and telluric acid, followed by back titrating excess oxidant with monovalent thallium.     

Formic acid as a reagent for alkaline permanganate : Potentiometric determination of formate

Oxidation of formate with permanganate in alkaline solutions yields a mixture of MnO₄^-2 and MnO₂. The reaction occurs slowly without an abrupt change in potential at the end-point. In 0.1N NaOH, at 80° C in the presence ofAg⁺ions or NaCl,the reaction is accelerated and yields MnO₂. The concentrations of formic acid obtained by oxidation with permanganate are comparable with those obtained by neutralization down to 2.295·10^-2N.Reduction of permanganate in the presence of Ba⁺² ions (alkalinity = 0.5 — 1.5N) or in the absence of Ba⁺ ions (alkalinity = 0.5 — 2.5N), gave accurate results for the permanganate concentration comparable with the results of the acid oxalate method.Formic acid is preferred to sodium formate on account of the greater stability of its solutions.     

Formic acid as a reagent for alkaline permanganate : Potentiometrrc determination of quadrivalent selenium

Se⁺⁴ can be determined by mixing with KMn0₄ in l N NaOH, stirring the mixture at room temperature and measuring the potential until equilibrium, which needs ~10–15 min. Excess KmnO₄ is then determined with formate.In the direct oxidation of Se⁺⁴ with MnO₄^- in the cold, and in the presence of 2.5 N NaOH and 10% NaCl, MnO₄^- → MnO₄^-2. At 90°C, and in the presence of 0.1 N NaOH 10% NaCl and 2— 3 ml of 0.5% AuCl₃, MnO₄^- → MnO₂. The reaction which is rather slow is accelerated by the above reagents.Reduction of MnO₄^- with Se⁺⁴ in l— 3 N NaOH yields MnO₄^-2.Like the indirect method, the direct potentiometric procedures yield good results.     

Oxidations with alkaline permanganate using formic acid for back-titration: Determination of lead and thallium

Pb⁺² (~37-0.6mg) and Tl⁺ (45-0.9 mg) can bc estimated by mixing with KmnO₄ in presence of Ba⁺² ions and I_NNaOH. The excess KmnO₄ is then titrated with formic acid.A mixture of Pb⁺² and Tl⁺ is oxidized simultaneously with KMn0₄ in 0.1N NaOH. Pb⁺² interferes also when precipitated as sulphate or tellurate. In presence of SO₄^-2 and telluric acid, thallium can be titrated only when its concentration is not less than 30 mg, below which lead seriously interferes. Tl⁺ can be accurately determined in the filtrate from the PbS0₄ precipitate.     

A new method for the potentiometric determination of lead with alkaline permanganate

A new method for the estimation of lead, based on its oxidation from the bivalent to the quadrivalent state by alkaline permanganate has been devised. The reaction takes place so rapidly in the presence of a mixture of ZnO and HgO that it can be followed potentiometrically. Oxidation of sodium plumbite with KMn0₄ leads to the formation of PbO and MnO. Reduction of KMnO4 with Pb⁺² ions or with sodium plumbite proceeds almost quantitatively in 2.5N NaOH in the absence of Ba⁺² ions and in 1–1.5N NaOH in the presence of these ions. Under these conditions Pb⁺² Pb⁺¹ and Mn0₄ MnO₄^-2, provided that the lead solution is not added too rapidly.     

Synthesis, Spectral, Thermal and CO2 Absorption Studies on Birnessites Type Layered MnO6 Oxide

Birnessite type layered MnO₆ oxides with increased crystallinity were synthesized from six carbohydrates and three dihydric phenols viz., dextrose, starch, fructose, galactose, maltose, lactose, catechol, resorcinol, quinol and KMnO₄ through the formation of a sol–gel. All of the MnO₆ oxides were characterized by powder XRD. The strong signal at 2θ ~ 12° corresponding to 7.4 Å refers to the Mn–Mn distance between the adjacent layers. The interlayer volume is dispersed with K⁺ ions and H₂O molecules. The presence of interlayer K⁺ ions is indicated by a signal at 25°, corresponding to a distance of 3.5 Å. IR spectra of the oxides show signature bands at ca. 500 cm^?1 due to the stretching modes occurring for MnO₆ entity. A broad band observed at ca. 3300 cm^?1 is due to interlayer water molecules. Thermal analysis indicated three stage decomposition with the formation of MnO₂ at ca. 600 °C through the intermediate formation of Mn(OH) _n . The MnO₆ exhibited a remarkable CO₂ scrubbing ability, which has also been investigated.     

2D → 3D corrugated structure self-assembled from 4,4′-methylenebis(N-(pyridin-2-ylmethylene)aniline and terephthalic acid: Crystal structure and selective anion separations via anion exchange

A new flexible cationic Zn(II)metal organic framework, {[Zn₂(BDC)_1.5(L)(DMF)]NO₃·DMF·solvent}_n, MOF 1 , which is a corrugated two-dimensional network, was synthesized by self-assembly of Zn(NO₃)₂.6H₂O with 4,4′-methylenebis(N-(pyridin-2-ylmethylene)aniline as a neutral ligand and terephthalic acid in dimethyl formamide (DMF) as solvent and characterized by X-ray diffraction. Because of the presence of uncoordinated nitrate (NO₃⁻) ions in the channels, the compound was employed for ion-exchange applications. We report a detailed study of the host–guest interaction for a cationic metal–organic framework (MOF) that can reversibly capture nitrate. The recrystallization of the MOF was evaluated by monitoring the anion exchange dynamics using a combination of powder X-ray diffraction and Fourier transform infrared spectra with various kinds of foreign anions. This MOF showed fast and highly efficient Cr₂O₇²⁻ and CrO₄²⁻, N₃⁻, MnO₄⁻, and SCN⁻ exchange. The trapping capacities of Cr₂O₇²⁻, CrO₄²⁻, N₃⁻, MnO₄⁻, and SCN⁻ were 105,138, 44,104, and 25mg/g at 25°C after 3h, respectively, and there was good recyclability for capturing N₃⁻ and SCN⁻. {[Zn₂(BDC)_1.5(L)(DMF)]NO₃}_n exhibited anion exchange selectivity of SCN⁻ in a solution containing a mixture of 0.025mmol N₃⁻, SCN⁻, CrO₄⁻²⁻, Cr₂O₇²⁻, and MnO₄⁻ for 3h and exhibited anion exchange selectivity for SCN⁻ and Cr₂O₇²⁻ in a solution containing a mixture of 0.001mmol N₃⁻, SCN⁻, CrO₄²⁻, Cr₂O₇²⁻, and MnO₄⁻.     

Spectrophotometric determination of osmium : O-Aminophenol-p-sulphonic acid as a reagent

o-Aminophenol-p-sulphonic acid is suggested as a very sensitive reagent for spectrophotometric determination of osmium (VI) and (VIII) at pH 2 5–4. The absorption maximum is at 440 mμ and the optimum concentration range is from 2 to 8 p p m of osmium Moderate amounts of Pd⁺², lr⁺⁴, WO₄^-2, Cr⁺³, Zn⁺², Zr⁺⁴, Mg⁺², Ba⁺² and Sr⁺² do not interfere     

Variation of the composition and properties of lithium manganese oxide spinel in lithiation-delithiation cycles

The behavior of the variable-composition spinel Li_{1 + x} Mn_{2 ? x} O₄ is examined in repeated cycles consisting of lithiation in 0.2 M LiOH and delithiation in 0.3 M HNO₃. For 0 < x < 0.33, delithiation is accompanied by the redox reaction 2Mn³⁺ → Mn⁴⁺ + Mn²⁺ and Li⁺ ? H⁺ ion exchange. The spinel undergoes partial conversion into λ-□MnO₂. Vacancies (□) build up at the 8a sites of the spinel structure. Mn²⁺ ions pass into the solution, and, accordingly, the spinel dissolves. Lithiation is accompanied by the redox reaction 4Mn⁴⁺ → 3Mn³⁺ + Mn⁷⁺ and ion exchange, and the proportion of vacancies □ at the 8a sites of the spinel structure decreases. The spinel undergoes partial dissolution because of Mn²⁺ and MnO _? ⁴ ions passing into the solution. The Li⁺ selectivity of the spinel is the property of the crystallite core. The crystallite surface is capable of sorbing Na⁺ ions.     

A binder-free thin film anode composed of Co2 +-intercalated buserite grown on carbon cloth for oxygen evolution reaction

We present a binder-free catalytic anode for highly efficient and stable oxygen evolution reaction in alkaline media. The catalyst consists of a thin film of buserite-type layered manganese dioxide (MnO₂) intercalated with Co^2 + ions, resulting from electrodeposition of the layered MnO₂ film with tetrabutylammonium (Bu₄N⁺) ions on a carbon cloth, followed by ion-exchange of the initially incorporated Bu₄N⁺ with Co^2 + in solution. The electrode is capable to produce a current density of 10 mA cm^− 2 at an overpotential (η) of 377 mV with a Tafel slope of 48 mV dec^− 1, much superior to the layered MnO₂ without Co^2 +.     

A heterometric micro-determination of lead with sodium diethyldithiocarbamate

The reaction between lead and sodium diethyldithiocarbamate is studied hcterometrically. The influence of the milieu, conditions of acidity and of different complexing agents, was studied. 0.02–0.04 mg lead per ml of solution can be determined either alone or in the presence of large excesses of other metals. A titration is carried out at 20°C in 8–15 minutes with an error of 0.0–1.0%. The analysed solution may contain ~ 99.5% of the following cations: Ca⁺². Sr⁺², Ba⁺², Mg⁺² Zn⁺², Mn⁺², Ni⁺², Co⁺², Al⁺³, Cr⁺³, Fe⁺³, Cd⁺². Cu⁺², Sb⁺³, Hg⁺², Ag⁺.     

Ba5[CrN4]N: Das erste Nitridochromat(V)

Ba₅[CrN₄]N: The First Nitridochromate(V) Ba₅[CrN₄]N is prepared by reaction of mixtures of Li₃N, Ba₃N₂ and CrN/Cr₂N (1 : 1) (molar ratio Li : Ba : Cr = 3 : 5 : 1) in tantalum crucibles at 700°C with flowing nitrogen (1 atm) within a period of 48 h. After cooling down to room temperature (60°C/h) black-shining single crystals of the ternary phase with a platy habit are obtained (monoclinic, C2/m; a = 1054.0(2) pm, b = 1170.9(3) pm, c = 937.7(2) pm, b? = 110,79(2)°; Z = 4). The crystal structure contains isolated complex anions [Cr^VN₄]^7? which nearly satisfy the ideal tetrahedral symmetry (Cr? N [pm]: 2 × 175.3(4), 2 × 175.8(5); N? Cr? N [°]: 106.8(2), 109.5(2), 2 × 109.9(2), 2 × 110,3(2)). The coordination sphere for each of the terminal nitride functions of the complex anions is completed by five neighbouring Ba²⁺ ions (distorted CrBa₅ octahedra). The octahedra are connected via common CrBa₂ faces as well as CrBa edges thereby forming condensed tetrameric octahedral groups. The isolated nitride ions which are also present in the crystal structure of Ba₅[CrN₄]N are in an octahedral environment of Ba²⁺ ions. The presence of a d¹-System (Cr(V)) is confirmed by magnetic susceptibility data.     

Solvent Effect on Rotational Correlation Times of Symmetric Tetraalkylammonium Ions

The overall rotational correlation times of symmetric tetraalkylammonium ions, R ₄N⁺ (R = ethyl, n-propyl, n-butyl, and n-pentyl), in various solvents were determined by the measurements of the ¹³C NMR spin-lattice relaxation times and the nuclear Overhauser enhancement factors of each α-carbon, considering the contribution of the internal rotation around the N—C bond. Except in water, the observed solvent dependencies of the rotational correlation times, τ_r, showed good correlations with those predicted from an electrohydrodynamic (Hubbard–Onsager–Felderhof) model. The correlation times of R ₄N⁺ increased as the size of the alkyl groups became larger. In the case of the n-Bu₄N⁺ and the n-Pen₄N⁺ ion, the τ _r values were similar to or even higher than those predicted by the HOF model under the stick hydrodynamic boundary condition, in spite of the fact that the ions were too small to allow the solvent to be regarded as a hydrodynamic or a dielectric continuum. A comparison of the results with the rotations of other pseudotetrahedral ions, e.g., tetraphenylborate and tetraphenylarsenium ions and with the translation of the R ₄N⁺ ions suggests that a considerable part of the rotational friction for R ₄N⁺ is brought about by pushing aside the solvent in the spaces between the alkyl groups of R ₄N⁺. A significant slowing in the rotation in water was observed for the n-Pr₄N⁺, n-Bu₄N⁺, and n-Pen₄N⁺ions; the extent of this effect increased with increasing size of the alkyl group. The increase in friction was related to the hydrophobic hydration of the R ₄N⁺ ions.     

Un réactif spécifique du germanium: la phénylfluorone

Based on the action of methyl fluorone on Ge(IV) the use of this reagent for the detection of germanium is described. It is necessary to treat with 6N HCl to make this reaction specific.However, another derivative of fluorone, namely phenyl fluorone, is still better for identifying Ge(IV). By placing a drop of the solution under test, previously strongly acidified (3 N to 6N in HCl), on a phenyl fluorone reagent paper and adding 2 or 3 drops of 6 N HNO₃, a. sensitive and specific reaction for germanium is obtained.The only interfering ions are those of strong oxidising agents (Ce⁺⁴, Cr⁺⁶, Mn⁺⁷, etc.) which destroy the reagents and must be eliminated in the first place.Other ions and ions of the group of the sulphides soluble in alkalisulfides do not interfere, even in the proportion of 100 parts by weight, to 1 of Ge. The limit of dilution is about 10^-5.5.     

Determination of hydrogen ion by ion chromatography (IC) with sulfonated cation-exchange resin as the stationary phase and aqueous EDTA (ethylenediamine-N,N,N′,N′-tetraacetic acid) solution as the mobile phase

An ion chromatographic (IC) method has been developed for determination of hydrogen ion (H⁺). It is based on the use of sulfonated cation-exchange resin as stationary phase, aqueous ethylenediamine-N,N,N′,N′-tetraacetic acid (dipotassium salt, EDTA-2K, written as K₂H₂Y) solution as mobile phase, and conductivity for detection. H⁺ was separated mainly by cation-exchange, but its elution was accelerated by the presence of EDTA. The order of elution for the model cations was H⁺ > Li⁺ > Na⁺ > NH₄ ⁺ > Ca²⁺ > > Mg²⁺. A sharp and highly symmetrical peak was obtained for H⁺ and this was attributed to the capacity of H₂Y₂ ^2– to receive and bind H⁺. H⁺ was detected conductiometrically and detector response (reduction in conductivity as a result of H⁺+H₂Y^2–→H₃Y^–) was linearly proportional to the concentration of H⁺ in the sample. The detection limit for H⁺ with this IC system was better than 4.7 μmol L^–1. A significant advantage of this method was the ability to separate and determine, in one step, H⁺ and other cations. The successful determination of H⁺ and other cation species in real acid-rain samples demonstrated the usefulness of this method.