I.A. Ismail

Applications involving oxidation with ethanolic iodine. Rapid potentiometric method for some reductants

Abstract Rapid potentiometric method was adopted for the determination of small amounts of hexacyanoferrate(II), thiosulfate, thiocyanate, and ascorbic acid, based on oxidation with ethanolic iodine at different pH values and subsequently titration of iodide with mercury(II) using silver amalgam as indicator electrode. The potential breaks at the vicinity of the endpoints were sharp enough for their accurate detection. The method provides for accurate determination of small amounts of some reductants of analytical importance.

Applications involving oxidation with KBrO3: I. Rapid potentiometric method for manganese alone or in steel and some ores

Abstract A rapid and reliable method is developed for the determination of manganese based on oxidation of the divalent cation with a known excess of KBrO 3 to the tetravalent state. The unreacted oxidant as well as Mn(IV) are then reduced with H 2 SO 3 to Br − and Mn(II). The resulting Br − is titrated with Ag 2 SO 4 using silver metal as the indicator electrode. K 2 SO 4 is added to increase sensitivity and establish equilibrium in the vicinity of the end point. Fe(III) when present is also reduced with SO 2 to the divalent state, which can be reoxidized with Br 2 . The equivalent amount of bromide is again titrated with Ag 2 SO 4 . The method provides for the simultaneous determination of Mn and Fe and finds application to some ores and steels.

Rapid potentiometric methods for vanadium and for analysis of ferrovanadium and some vanadium steels

Abstract Rapid and reliable potentiometric methods are given for determination of vanadium based on titrating unreacted KBr or KI in H 2 SO 4 acid medium with Hg(I) or Hg(II), using silver amalgam as the indicator electrode. The methods are successfully applied to the analysis of ferrovanadium, three varieties of vanadium steels and synthetic mixtures of about identical constitution. In all cases the potential breaks were sharp enough for the accurate determination of the end points.

Determination of gold(III) alone or in some mixtures and alloys by potentiometric titration of iodide

Abstract The present work is an application of iodide to the reduction of gold(III), in an attempt to develop new method for gold(III) based on potentiometric back-titration of the excess of iodide with mercury(II). Although it was proved by calculation that the reduction of tetrachloroaurate to the metal should proceed quantitatively to completion, yet our experiments showed that the reduction under ordinary conditions, gave Au(I) in the form of a white precipitate of AuI. We succeeded to push the reduction with iodide to the metal by an excess of ethanol-ether catalyzed iodide at somewhat elevated temperature. With the experimental conditions established a reliable procedure have been developed involving a potentiometric finish which enabled accurate determination of gold(III), either alone or in some of its alloys.

Application of arsenite reduction to the potentiometric determination of gold and to the analysis of mixtures and alloys

Abstract This investigation is an application of the method involving reduction with arsenite to the determination of gold. Binary and ternary gold containing mixtures as well as some important Egyptian gold alloys were completely analyzed. The reversibility of As(V) and Cu(II) toward iodide makes possible the determination of Ag and Au in presence of each other without the interference of As(V) or Cu(II). The more insoluble AgI makes possible the determination of the metal in the presence of chloride ions. The nonreactivity of both Ag(I) and Au(III) toward EDTA, makes possible the determination of Cu(II) in the presence of both cations. The present methods have the advantages over the classical ones of being simple rapid and reliable.

Applications involving oxidation with potassium bromate: II. Potentiometric titration of chromium alone or in mixtures

Abstract A rapid and reliable determination of chromium was developed based on bromate oxidation of chromium(III) to chromium(VI). The reaction is complete under weakly acidic conditions and with cobalt(II) present as a catalyst. Unreacted bromate and chromium(VI) are then reduced with sulfite to bromide and chromium(III). The bromide is titrated potentiometrically with mercury(I) using a silver amalgam indicator electrode. Iron(III) if present is reduced by sulfite to iron(II) and does not interfere. Some binary and ternary metal mixtures containing chromium can be resolved by the determination of chromium, alone or with another metal, by the above procedure coupled with procedures for further sample portions involving the potentiometric titration of unreacted CyDTA or iodide, or both, with mercury(II).

Use of arsenite reduction in potentiometric methods for arsenic(III) or higher valent lead, manganese, chromium, and vanadium in some industrial products

Abstract A simple, rapid, and reliable method is given for determination of As(III) based on arsenite reduction of alcoholic iodine and titration of the equivalent iodide with Hg(II) using silver amalgam as the indicator electrode. Arsenite reduction is applied to the estimation of lead in minium, manganese in duralumin, chromium in zinc chromate, and vanadium and chromium in ilmenite, the excess of arsenite being determined by the same method used for As(III). The endpoints are accurately determined with very satisfactory potential breaks.

Analysis of tungsten-containing mixtures and some alloy steels by potentiometric titration methods

Reliable potentiometric titration methods are adopted for the analysis of tungsten mixtures analogous to some industrially important alloys such as low alloy tap steel, tungsten chisel, and high speed steels. Tungsten is separated as Hg2WO4 and unreacted Hg(I) is titrated with KBr. The techniques of oxidation with I2 or reduction with KI and use of the selective arsenite reduction of Cr(VI) and/or Mn(IV) in the presence of V(V) or Fe(III) make it possible to determine alloy components without tedious separations. In all titrations the potential break is sharp enough for the precise establishment of the end point.

Potentiometric determination of tin analysis of mixtures as well as brass and bronze

Abstract A reliable potentiometric method was developed for determination of tin, based on reduction of Sn(IV) to Sn(II) using nascent hydrogen liberated from the reaction between Al metal and H2SO4. A process of reoxidation of bivalent tin ions to their original state of valency was carried out by ethanolic iodine. The liberated iodide is titrated against Hg2+ using Ag/amalgam as indicator electrode coupled with SCE. The method finds application in the analysis of some binary and ternary mixtures containing tin as well as brass and bronze alloys.

Applications involving oxidation with KBrO3: Potentiometric determination of some inorganic white and yellow pigments

Abstract Rapid potentiometric methods were given for determination of some sulfide and chromate pigments in pure as well as adulterated samples. The methods are based on oxidation of S 2− or Cr 3+ with known excess of KBrOs 3 to the corresponding (S ↓) or Cr 6− . Oxidation of trivalent chromium proceeds only toward completion in presence of a catalyst such as Co 2+ . Sulfide oxidation needs gradual liberation of H 2 S—which can be achieved by dropwise additions of the acid—together with the presence of excessive amount of water, in order to obtain accurate results excess oxidant was subsequently reduced with SO 2 to produce Br − that can be titrated against Hg(I). The potential breaks are quite sharp for accurate determination of the equivalent points.