Results 1 - 10 of 4221
Results 1 - 10 of 4221. Search took: 0.028 seconds
|Sort by: date | relevance|
[en] Using the methods of thermogravimetry, infrared spectroscopy and analytical analysis electroreduction of WO42- and MoO42- from fluoride-containing electrolyte is studied. It is established that products of incomplete reduction of tungstate- and molybdate ions present heterogeneous systems consisting of oxide-hydroxide compounds of lower valencies, possesing mixed conductivity. Complete reduction of WO42- and MoO42- to metal takes place at high concentrations of fluoride-ion (>= 50 g/l) and high current densities: 100-400 A/dm2 for molybdenum and 100-200 A/dm2 for tungsten
[en] The determination of 800 to 30 μg Pb(II) by potentiometric titration with molybdate by using a lead(II)-selective electrode was investigated. Under suitable conditions, 800 to 300 μg Pb(II) in aqueous solution by automatic or manual titration with 4x10-3 M molybdate can be determined with an accuracy of +-0.57% and +-0.45% and a precision of +-0.43% and 0.30% (standard deviation = 0.25% and 0.17%, resp.). For determining amounts of Pb(II) below 300 μg, a 2x10-3 M molybdate solution has to be used. Although 300 to 100μg Pb(II) are determinable again in water with satisfactory results, the titration in 40% ethanol is however more reliable: in this medium, amounts of 300 to 30μg Pb(II) can be determined with an accuracy of +-1% and a precision of +-2% (standard deviation from 20 titrations of 100μg Pb(II)=0.60%). The titration of 300-800μg Pb(II) in water and of 30-300μg Pb(II) in 40% ethanol is also possible in 0.1 M NaNO3sub- snd 0.1 M NaClO4sub- medium and can be used in the lead determination in organic compounds after mineralization with HNO3sub-HClO4sub-H2O2. (Author)
[en] The deflection of a He-Ne light beam by polydomain gadolinium molybdate (GMO) crystals has been studied with respect to incidence angle αi on the sample at room temperature. The A and B deflected beams do not cross each other during the αi variation, in contrast to results and calculations previously published. The model using the Fresnel equation confirms this result. The model presented is more accurate for numerical calculation than that using the Huygens construction. (author)
[en] The crystal structure of Na2[(NpO2)2(MoO4)2(MoO4)2H2O] · H2O (I) is determined (CAD-4 SDP automated diffractometer, λMoKα, graphite monochromator). Crystallographic data: a = 9.004(2) angstrom, b = 10.980(2) angstrom, c = 13.229(2) angstrom, β = 102.46(2)degrees, V = 1277.0(8) angstrom 3, space group P21/n, Z = 4, d(calcd.) = 4.89 g/cm3, μ(MoKalpha) = 163 cm-1, R = 0.028, Rw = 0.033 [for 1467 reflections with sin θ/λ > 0.20 angstrom -1 and I > 3σ(I)]. The crystal structure of I is of the framework type. Coordination polyhedra of both crystallographically independent neptunium atoms are pentagonal bipyramids, which are combined in pairs sharing an edge through the coordination of one neptunyl ion by the other and a bridging oxygen atom of the molybdate moiety. MoO4 moieties act as tridentate and quadridentate bridges. One of the two water molecules is involved in the Np coordination sphere. The second water molecule and Na+ ions are situated in the channels of a three-dimensional neptunyl-molybdate framework
[en] In this system hydroquinone is oxidized to pbenzoquinone by H2O2. 2 aniline are added, in successive stages, to pbenzoquinone, to yield the disubstituted quinone as the final product. 20 The UV-VIS spectrum of the product in aqueous solution presented in Figure 1. It is obvious that a strong absorption peak with a maximum at 550 nm is formed. In conclusion, the new method based on the addition product formation has been demonstrated to be reliable and with acceptable sensitivity for the determination of hydrogen peroxide in verities of product.