Silver reductor

The mercury(l) chloride is unaffected by oxidants during the subsequent titration. Sulfite (or SO2) and hydrogen sulfide are alternative reductants. Metals may also be used. Small pieces of metal (zinc - a Jones reductor, silver - a Walden reductor) are used to fill a column, through which the analyte solution is passed. The effluent is titrated with oxidant. A comparison of the reduction products of the two reductor columns is given in Table 3. 

Discussion. Copper(II) ions are quantitatively reduced in 2M hydrochloric acid solution by means of the silver reductor (Section 10.140) to the copper(I) state. The solution, after reduction, is collected in a solution of ammonium iron(III) sulphate, and the Fe2+ ion formed is titrated with standard cerium(IV) sulphate solution using ferroin or AT-phenylanthranilic acid as indicator. 

Procedure (copper in crystallised copper sulphate). Weigh out accurately about 3.1 g of copper sulphate crystals, dissolve in water, and make up to 250 mL in a graduated flask. Shake well. Pipette 50 mL of this solution into a small beaker, add an equal volume of ca AM hydrochloric acid. Pass this solution through a silver reductor at the rate of 25 mL min i, and collect the filtrate in a 500 mL conical flask charged with 20 mL 0.5M iron(III) ammonium sulphate solution (prepared by dissolving the appropriate quantity of the analytical grade iron(III) salt in 0.5M sulphuric acid). Wash the reductor column with six 25 mL portions of 2M hydrochloric acid. Add 1 drop of ferroin indicator or 0.5 mL N-phenylanthranilic acid, and titrate with 0.1 M cerium(IV) sulphate solution. The end point is sharp, and the colour imparted by the Cu2+ ions does not interfere with the detection of the equivalence point. 

It must be emphasised that if hydrochloric acid has been employed in the original solution of the iron-bearing material, the volume should be reduced to ca 25 mL and then diluted to ca 150mL with 5 per cent sulphuric acid. The determination is carried out as detailed above, but 25 mL of Zimmermann-Reinhardt or preventive solution must be added before titration with standard potassium permanganate solution. For the determination of iron in hydrochloric acid solution, it is more convenient to reduce the solution in a silver reductor... 

The silver reductor has a relatively low reduction potential (the Ag/AgCl electrode potential in 1M hydrochloric acid is 0.2245 volt), and consequently it is not able to effect many of the reductions which can be made with amalgamated zinc. The silver reductor is preferably used with hydrochloric acid solutions, and this is frequently an advantage. The various reductions which can be effected with the silver and the amalgamated zinc reductors are summarised in Table 10.11. ... 

Silver reductor hydrochloric acid solution Amalgamated zinc (Jones) reductor sulphuric acid solution... 

The dark silver chloride coating which covers the silver of the upper part of the reductor when hydrochloric acid solutions are employed moves further down... 

Although as already stated the use of metal amalgams, and in particular use of the Jones reductor or of the related silver reductor, is the best method of reducing solutions in preparation for titration with an oxidant, it may happen that for occasional use there is no Jones reductor available, and a simpler procedure will commend itself. In practical terms, the need is most likely to arise in connection with the determination of iron, for which the reduction of iron(III) to iron(II) may be necessary. 

Reductant equivalent weights of, 847 Reduction 409 by chromium(II) salts, 409 by hydrogen sulphide, 416 by Jones reductor (zinc amalgam), 410 by liquid amalgams, 412 by silver reductor, 414 by sulphurous acid, 416 by tin(II) chloride, 415 by titanium(II[), 410 by vanadium(II), 410 see also Iron(III), reduction of Reduction potentials 66 Reference electrodes potentials, (T) 554 Relative atomic masses (T) 819 Relative error 134 mean deviation, 134... 

Table 5.6 A comparison of silver and Reduction effected by silver reductor Fe3+ + e- = Fe2+...

Walden reductor A column packed with silver and eluted with HC1. Analyte is reduced during passage through the column. The reduced product is titrated with an oxidizing agent. 

REDUCTION EFFECTED BY SILVER REDUCTOR REDUCTION EFFECTED BY JONES REDUCTOR... 

Reductor columns have been prepared from zinc, silver, lead, cadmium, bismuth, antimony, nickel, copper, tin, and iron. 

The silver reductor, often called the Walden reductor, is much more selective than zinc as a reducing agent. A hydrochloric acid solution is always used. The electrode potential varies with the concentration of chloride therefore the acid concentration is more critical than with the zinc reductor. From... 

In bromide solutions the formal potential of the silver reductor is 0.13 V lower, and reductions take place more readily. It is used with 0.1 to 4 M hydrogen bromide. 

Walden reductor A column packed with finely divided silver granules used to prereduce analytes. 

The optimal acidity corresponds to pH 3.0 0.2. Only Au, Hg, and Pt interfere in determination of palladium. The reaction of TMK with Hg(ll) is slower (about 2 h). Oxidants also interfere the reagent behaves as a reductor. Chloride masks silver ions. EDTA can be used to prevent hydrolysis of some metal ions. 

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