Zinc/ions/salts determination

The metals can be activated toward alkalies by coupling them with other metals, just as they are activated toward water and acids. When zinc is in contact with iron the former reacts rapidly with a warm solution of sodium hydroxide. Hydrogen is evolved from the iron and the zinc passes into solution as sodium zincate, NagZnOg. Tin behaves in a similar way and sodium stannite, NagSnOa, is formed. It should be noted that in these cases the metal that dissolves is the one which forms a hydroxide soluble in sodium hydroxide. When two metals are coupled in neutral or acid solution hydrogen is evolved from the metal having the lower solution pressure— that is, the one lower in the electromotive series. When the solution contains an alkali, this is not always the case. Zinc is above and tin is below iron in the electromotive series, but when activated by iron in the presence of an alkali they each dissolve. The solubility of the hydroxide in alkalies is the determining factor in the reaction. The zinc that passes into solution is not presnt in the form of zinc ions, but as zincate ions, ZnOo— which result from the ionization of the salt formed. 

Optimal conditions for the precipitation of starch xanthate from sodium starch xanthate as the zinc salt have been determined as a xanthate degree of substitution greater than 0.02 and a zinc ion concentration in solution between 0.005 and 0.015 M. Other properties of the starch xanthates were also reported. Aqueous solutions of starch xanthate, butane-2,3-diol dixanthate and alkali-gelatinized starch have been treated with butane-2,3-diol diglycidyl ether and other diepoxides to produce viscous gels. Epoxy resins also reacted with xanthate to form viscous gels. Solids were precipitated from the gels and their compositions deduced from their elemental contents and infrared spectra. 

Carboxy groups present in polyvinyl alcohol are transformed into calcium salts and isolated. After hydrolysis, the calcium ions can be determined by using the zinc ethylenediaminetetraacetate complex. The current of the liberated zinc ions is then measured. 

BackTitrations. In the performance of aback titration, a known, but excess quantity of EDTA or other chelon is added, the pH is now properly adjusted, and the excess of the chelon is titrated with a suitable standard metal salt solution. Back titration procedures are especially useful when the metal ion to be determined cannot be kept in solution under the titration conditions or where the reaction of the metal ion with the chelon occurs too slowly to permit a direct titration, as in the titration of chromium(III) with EDTA. Back titration procedures sometimes permit a metal ion to be determined by the use of a metal indicator that is blocked by that ion in a direct titration. Eor example, nickel, cobalt, or aluminum form such stable complexes with Eriochrome Black T that the direct titration would fail. However, if an excess of EDTA is added before the indicator, no blocking occurs in the back titration with a magnesium or zinc salt solution. These metal ion titrants are chosen because they form EDTA complexes of relatively low stability, thereby avoiding the possible titration of EDTA bound by the sample metal ion. 

High tendency of ZnfSCN) ion to extraction into organic phase is widely used for zinc determination by extraction photometry method. Recently it was shown that when single-chai ged anions ai e exchanged for double-chai ged ones, the selectivity of this process depends on the number of methyl substitutients in quaternary ammonium salt (QAS) cation. 

The method may also be applied to the analysis of silver halides by dissolution in excess of cyanide solution and back-titration with standard silver nitrate. It can also be utilised indirectly for the determination of several metals, notably nickel, cobalt, and zinc, which form stable stoichiometric complexes with cyanide ion. Thus if a Ni(II) salt in ammoniacal solution is heated with excess of cyanide ion, the [Ni(CN)4]2 ion is formed quantitatively since it is more stable than the [Ag(CN)2] ion, the excess of cyanide may be determined by the Liebig-Deniges method. The metal ion determinations are, however, more conveniently made by titration with EDTA see the following sections. 

Phenolic antioxidants in rubber extracts were determined indirectly photometrically after reaction with Fe(III) salts which form a red Fe(II)-dipyridyl compound. The method was applicable to Vulkanox BKF and Vulkanox KB [52]. Similarly, aromatic amines (Vulkanox PBN, 4020, DDA, 4010 NA) were determined photometrically after coupling with Echtrotsalz GG (4-nitrobenzdiazonium fluoroborate). For qualitative analysis of vulcanisation accelerators in extracts of rubbers and elastomers colour reactions with dithio-carbamates (for Vulkacit P, ZP, L, LDA, LDB, WL), thiuram derivatives (for Vulkacit I), zinc 2-mercaptobenzthiazol (for Vulkacit ZM, DM, F, AZ, CZ, MOZ, DZ) and hexamethylene tetramine (for Vulkacit H30), were mentioned as well as PC and TLC analyses (according to DIN 53622) followed by IR identification [52]. 8-Hydroquinoline extraction of interference ions and alizarin-La3+ complexation were utilised for the spectrophotometric determination of fluorine in silica used as an antistatic agent in PE [74], Also Polygard (trisnonylphenylphosphite) in styrene-butadienes has been determined by colorimetric methods [75,76], Most procedures are fairly dated for more detailed descriptions see references [25,42,44],... 

Elemental composition Zn 63.24%, F 36.76%. ZnF2 may be characterized from its x-ray and other physical properties. The water of crystaUization in the tetrahydrate may be determined by thermogravimetric method. A small amount of compound is dissolved in water (anhydrous salt is very slightly soluble in water) and analyzed for fluoride ion by the electrode method or by ion chromatography. A diluted acid solution of the compound is analyzed for zinc by various instrumental methods (See Zinc). 

Water of crystaUization in hydrated salts can be measured by thermo-gravimetric analysis. Zinc can be analyzed in an aqueous solution by AA or ICP. Sulfate can be identified by precipitation with barium chloride solution or by ion chromatography. The zinc content in the heptahydrate is determined by AA, ICP and other instrumental methods. 

The electrical conductivity.—E. Klein10 showed that if there is a difference between the conductivity of a mixture of salts in soln. and the mean conductivities of the separate constituents, a double salt is probably formed. The molecular conductivity of a salt, and if possible of its components at different dilutions, has been employed to determine the number of component ions in a soln. it was used, for example, by A. Werner (1893-1901) with the cobalt, chromium, platinum, and other ammines.11 In moderately cone. soln. the double salts are but little ionized, and the difference between the conductivities of eq. soln. of potassium zinc chloride, ZnCl2.2KCl, and of the sum of the constituents amounts to nearly 36 per cent., a value which is greatly in excess of that whieh would be due to the mutual influence of salts with a common ion. Tables of the molecular conductivities of salts show that with very few exceptions, at a dilution of 1024 litres and 25°, most salts have conductivities approximating those indicated in Table XIX. 

In salts of [Zn(NCS)4], the thiocyanate ligand is N-bonded, whereas it is S-bonded to cadmium in [Cd(SCN)4] salts, reflecting the respective hard and soft characters of the respective metal ions. Zinc complexes with the azide ion are well known crystallographic determinations of the structures of the compounds M2Zn(N3)4 (M = K or Cs) show the presence of discrete [Zn(N3)4] tetrahedra with linear azide groups. Some of the complexes in this category, such as those with hydrazine and azide, for example [Zn(N2H4)2(N3)2], are of interest as primary explosives and care is needed in their manipulation. The 2,2 -dipyridylamine-azide complexes [Zn(dpa)(N3)2] and [Zn(dpa)(N3)(N03)], which have infinite 2D and 3D structures respectively, display fluorescence and phosphorescence. ... 

For current densities at or above 0.2mA/cm, the sensation associated with transdermal iontophoresis is determined by the type of ion being delivered into the skin. When human subjects compared the sensation experienced during iontophoresis of different salt solutions applied to the right and left forearms, delivery of calcium caused less sensation than delivery of phosphate, magnesium, and zinc, which caused less sensation than delivery of chloride, acetate, citrate, and sulfate, which in turn caused less sensation than delivery of lithium, potassium, and sodium. In general, multivalent ions were found to cause less sensation than monovalent ions. ... 

Danforth and Dix [75] compared the behaviours of both zinc and magnesiimi (see below) oxalates. Kinetic measurements were made by independent determinations of the yields of carbon monoxide and of carbon dioxide at appropriate reaction times. The kinetics of reaction of the zinc salt were fitted by the Prout-Tompkins equation (620 to 645 K) and i , = 196 kJ mol. The activation step was identified as the formation of the radical ion 204, following the transfer of an electron to a cation. The decomposition of this activated species was then accelerated by the product zinc oxide. The term accelerated rather than catalysed was preferred because the magnitude of was not decreased by the presence of the oxide product. 

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