Titanium titration with

With the exception of iron(II) and uranium(IV), the reduced solutions are extremely unstable and readily re-oxidise upon exposure to air. They are best stabilised in a five-fold excess of a solution of 150g of ammonium iron(III) sulphate and 150 mL of concentrated sulphuric acid per litre [approximately 0.3M with respect to iron] contained in the filter flask. The iron(II) formed is then titrated with a standard solution of a suitable oxidising agent. Titanium and chromium are completely oxidised and produce an equivalent amount of iron(II) sulphate molybdenum is re-oxidised to the Mo(V) (red) stage, which is fairly stable in air, and complete oxidation is effected by the permanganate, but the net result is the same, viz. Mo(III)- Mo(VI) vanadium is re-oxidised to the V(IV), condition, which is stable in air, and the final oxidation is completed by slow titration with potassium permanganate solution or with cerium(IV) sulphate solution. 

Where the reduction potentials of two analytes are sufficiently different a mixture may be analysed. Titanium(III), = 0-lOV may be titrated with cerium(IV) in the presence of iron(II), =0.77 V usjng methylene blue as indicator. Subsequently the total, iron plus titanium, may be determined using ferroin as indicator. The determination of iron is illustrative of some practical problems which are encountered in direct titration procedures. 

Our studies of Ti02 and Zr02 nano-sized particles prepared by a sol-gel precipitation method [101] (titration with NH4OH and further stabilization of the precipitate with HNO3) showed interesting difference between titanium and zirconium dioxides [89, 90]. Fig. 8.1 performs a typical EPR spectrum of the N02 radical adsorbed on the surface of NC Ti02 thermally treated for 1 h at 200° (parameters are listed in Table 8.4). A similar one with lower intensity has been observed in the case of Zr02 [90],... 

Apparatus The apparatus for determining total color by titration with titanium chloride (TiCl3) is shown in Fig. 23. 

As the ferrous salt, Knecht used iron ammonium sulfate (Mohr salt) and oxidized this to ferric sulfate with 0.02 N potassium permanganate in sulfuric acid solution. The resulting ferric salt was then back-titrated with titanium trichloride solution. The other, equally simple method consists in dissolving pure iron wire in pure hydrochloric acid and oxidizing the ferrous chloride solution with a few drops of bromine. The excess bromine is removed by boiling and the solution is titrated with the titanium trichloride solution. 

The shape of the curve for an oxidation-reduction titration depends on the nature of the system under consideration. The titration curve in Fig. 7 is symmetric about the equivalence point because the molar ratio of oxidant to reductant is equal to unity. An asymmetrical curve results if the ratio differs from this value. Solutions containing two oxidizing or reducing agents yield titration curves containing two inflection points if the standard potentials for the two species are different by more than approximately 0.2 V. Fig. 8 shows the titration curve for a mixture of iron(II) and titanium(III) with cerium(rV). The first additions of cerium are used by more readily oxidized titanium(III) ion, thus, the first step in the titration curve corresponds to titanium and the second to iron. 

Volumetric determination may be made by reducing the titanium to the trivalent condition with zinc and then titrating with potassium permanganate, ferric chloride, or methylene blue.5... 

Chromiimi(lI) and titanium(II[I) are very powerful reducing agents, but they are readily air-oxidized and difficult to handle. The standard potential of the former is -0.41 V (Cr3+/Cr2+) and that of the latter is 0.04 V (TiO"+/Ti +). The oxidized forms of copper, iron, silver, gold, bismuth, uranium, tungsten, and other metals have been titrated with chromium(II). The principal use of Ti " " is in the titration of iron(in) as well as copper(II), tin(IV), chromate, vanadate, and chlorate. 

Sometimes, the reduced sample is rapidly air-oxidized and the sample must be titrated under an atmosphere of CO2, by the addition of sodium bicarbonate to an acid solution. Air must be excluded from tin(II) and titanium(III) solutions. Sometimes, elements rapidly air-oxidized are eluted from the column into an iron(IH) solution, with the end of the column immersed in the solution. The iron(III) is reduced by the sample to give an equivalent amount of iron(II), which can be titrated with dichromate. MoIybdenum(III), which is oxidized to molybdenum(VI) by the iron, and copper(I) are determined in this way. 

Macro quantities of selenium can be determined gravimetrically after reduction to the elemental form by various reagents such as tin (II) chloride, potassium iodide, or ascorbic acid (I). Ooba described a technique whereby the element is precipitated from perchloric acid solution with hydrazine (2). Selenium may be titrated with standard solutions of sodium thiosulfate, iodide, and ferrous, chromous, or trivalent titanium salts after oxidation to Se(VI) (I). Photometric and fluorometric methods based on formation of the piaselenol with diaminobenzidine or 2,3-diaminonaphthalene has been used for the determination of selenium (I, 3,4,5). Interfering elements such as As, Co, Cr, Cu, Fe, Hg, and Ni, are masked with EDTA or other chelating agents. 

A number of transition metals can be determined conveniently if their cations undergo a definite change of oxidation state see Oxidation Number) on titration with a standard solution of potassium permanganate, potassium dichromate, cerium(IV) sulfate, or ammonium hexanitratocerate(IV). Several visual indicators have been proposed, including diphenylamine and its derivatives, xylene cyanole FF, and especially A-phenylanthranilic acid and tris(l,10-phenanthroline)iron(II) sulfate ( ferroin ). Solutions of have been used in the determination of iron, copper, titanium, vanadium, molybdenum, tungsten, mercury, gold, silver, and bismuth, and standard solutions of and Sn F U, and and Mo have also... 

Peroxides can be reduced by excess iodide ion in acetic acid or isopropanol solvents, and the liberated iodine may be titrated with standard thiosulfate solution. Iodide ion, titanium(IV), ferrous ion, and N,N-dimethyl-p-phenylenediamine are some of the reducing reagents used for colorimetric analyses for trace peroxides. 

Most titrimetric methods for titanium dq>end on the reduction of Ti(IV) to Ti(III), followed by subsequent titration with a standard oxidizing solution [23]. The methods vary with the choice of reductant, the titrant, and with the method of detecting the endpoint. 

Genevois (1951) reviewed the methods used for color. He suggested bromination or titration with titanium trichloride at a high pH. Zinc has been used for anthocyanin reduction. However, oxidation of acidulated wine by means of permanganate is the commonest procedure. 

Reduction. Titanium(IV) is reduced to Ti by Nang, Mg, Zn, Zn g, A1 in acid, and Sn. With the Jones reductor (Znng), large amounts of the element may be determined volumetrically. The Ti is mixed with Fe sulfate, excluding air, and the Fe " produced is titrated with Mn04. ... 

A number of techniques other than titration with permanganate and iodimetry have been published in the last few years. Thus, titration with titanium sulfate has been used by Weil-Malherbe and Schade (365). Gold-blith and Proctor (165) as well as Atami et al. (33) add excess acid permanganate to the test solution and determine its utilization spectrophoto-metrically. 

Reduction. Triaryknethane dyes are reduced readily to leuco bases with a variety of reagents, including sodium hydrosulfite, 2inc and acid (hydrochloric, acetic), 2inc dust and ammonia, and titanous chloride in concentrated hydrochloric acid. Reduction with titanium trichloride (Knecht method) is used for rapidly assaying triaryknethane dyes. The TiCl titration is carried out to a colorless end point which is usually very sharp (see Titanium COMPOUNDS, inorganic). 

It is possible to titrate two substances by the same titrant provided that the standard potentials of the substances being titrated, and their oxidation or reduction products, differ by about 0.2 V. Stepwise titration curves are obtained in the titration of mixtures or of substances having several oxidation states. Thus the titration of a solution containing Cr(VI), Fe(III) and V(V) by an acid titanium(III) chloride solution is an example of such a mixture in the first step Cr(VI) is reduced to Cr(III) and V(V) to V(IV) in the second step Fe(III) is reduced to Fe(II) in the third step V(IV) is reduced to V(III) chromium is evaluated by difference of the volumes of titrant used in the first and third steps. Another example is the titration of a mixture of Fe(II) and V(IV) sulphates with Ce(IV) sulphate in dilute sulphuric acid in the first step Fe(II) is oxidised to Fe(III) and in the second jump V(IV) is oxidised to V(V) the latter change is accelerated by heating the solution after oxidation of the Fe(II) ion is complete. The titration of a substance having several oxidation states is exemplified by the stepwise reduction by acid chromium(II) chloride of Cu(II) ion to the Cu(I) state and then to the metal. 

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