Antimony, iodine titration

The tartrated antimony salts are estimated by the iodine titration method given on p. 78, after dissolving about 0 5 g in water. Antimony potassium tartrate C4H407SbK, Mol. Wt. 324 9,1 ml 0-lN 0 01625 g antimony sodium tartrate, C4H407SbNa, Mol. Wt. 308 8,1 ml0 lN = 0 01544 g. 

The presence of sodium metabisulphite in certain formulations interferes with the determination of trivalent antimony by iodine titration but this difficulty may be overcome by the addition of 3 ml of formaldehyde to the solution acidified with hydrochloric acid and allowing to stand for five minutes before titration. 

Arsenious oxide, trivalent antimony (73), sulfurous acid (74), hydrogen sulfide (75), stannous ion, and thiocianate (76) have been recommended for the titration of iodine. However, none of these appears to have a greater sensitivity for the deterrnination of minute quantities of iodine than thiosulfate. Organic compounds such as formaldehyde (77), chloral hydrate (78), aldoses (79), acetone (70,80), and hydroquinone have also been suggested for this purpose. 

Consistent with this, dissolution of KF increases the conductivity and KIFe can be isolated on removal of the solvent. Likewise NOF affords [NO]+[IF6] . Antimony compounds yield ISbFio, i-2. [IF4]+[SbF6], which can be titrated with KSbFfi. However, the milder fluorinating power of IF5 frequently enables partially fluorinated adducts to be isolated and in some of these the iodine is partly oxygenated. Complete structural identification of the products has not yet been established in all cases but typical stoichiometries are as follows ... 

A similar procedure may also be used for the determination of antimony(V), whilst antimony (III) may be determined like arsenic(III) by direct titration with standard iodine solution (Section 10.113), but in the antimony titration it is necessary to include some tartaric acid in the solution this acts as complexing agent and prevents precipitation of antimony as hydroxide or as basic salt in alkaline solution. On the whole, however, the most satisfactory method for determining antimony is by titration with potassium bromate (Section 10.133). 

Discussion. Iodine (or tri-iodide ion Ij" = I2 +1-) is readily generated with 100 per cent efficiency by the oxidation of iodide ion at a platinum anode, and can be used for the coulometric titration of antimony (III). The optimum pH is between 7.5 and 8.5, and a complexing agent (e.g. tartrate ion) must be present to prevent hydrolysis and precipitation of the antimony. In solutions more alkaline than pH of about 8.5, disproportionation of iodine to iodide and iodate(I) (hypoiodite) occurs. The reversible character of the iodine-iodide complex renders equivalence point detection easy by both potentiometric and amperometric techniques for macro titrations, the usual visual detection of the end point with starch is possible. 

The quantity of antimony in a solution can be determined by converting it to the +3 oxidation state and titrating with standard iodine in bicarbonate solution ... 

Antimony(ni) is titrated to antimony(V) in neutral or slightly alkaline solution with iodine to a blue starch end point. The iodine is standardized against primary standard arsenic(in) oxide. Tartaric acid is added to complex the antimony and prevent its hydrolysis to form insoluble basic salts such as SbOCl and Sb02Cl (which form in slightly acid and neutral solution). 

Dr Clark, in Journ. Hoc. Chem. Ind., 1896, recommends for antimony ores and alloys a modification of Mohr s method t of titration with solution of iodine —... 

Dissolve from 0-5 to 2 g of the substance in water or dilute hydrochloric acid, add about 5 g of sodium potassium tartrate to keep antimony in solution and then a slight excess of sodium bicarbonate or 2 g of borax. Titrate at once with O IN iodine. 1 ml 0 1N = 0 007288 g SbgOa-... 

A general method for the estimation of antimony, either in organic combination or as an inorganic salt, is the bromate titration method. It is preferable to the method of titration with iodine in the presence of bicarbonate unless the material being estimated is a fairly pure salt, since the solution being titrated may be coloured somewhat and there is often difficulty in the use of starch as indicator. The bromate method is applicable in the presence of arsenic. 

Sodium antimonylgluconate is a trivalent antimony derivative. The total antimony is determined after wet combustion by reduction with potassium iodide in the presence of tartaric acid, boiling off the iodine completely, making alkaline with sodium hydroxide, then just acid with dilute sulphuric acid, and titrating in bicarbonate solution with 0-05N iodine. 1 ml = 0 003044 g Sb. Trivalent antimony can be determined polarographically as described above directly on the material. 

The trivalent antimony in this preparation can be determined without destruction of organic matter by dissolving about 0 5 g in dilute acetic acid, adding an excess of 0 05N iodine and titrating back with thiosulphate after standing for five minutes. 1 ml 0 05N = 0 003044 g trivalent Sb. 

Gravimetric methods for the determination of Sb(III) as trisulphide or as 8620 are not very specific. A quick volumetric method for Sb(III) is based on its oxidation by iodine, using starch as indicator. On the other hand, Sb(V) oxidises iodide to iodine which can be titrated against thiosulphate. Antimony as well as arsenic and bismuth can be determined by atomic absorption spectroscopy, the suitable wavelengths and concentration ranges and other conditions are usually supplied by the manufacturer. A useful spectrophotometric method is based on the yellow complex tetraiodobismuthate(III). 

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