Antimony , titration

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). 

Photometric titrimetry can be used for simultaneous determination of arsenic(III) and antimony(III) in a mixture. In acidic solutions, arsenic(III) can be oxidized to arsenic(V) and antimony(III) can be oxidized to antimony(V) by titration with a solution of potassium bromate and potassium bromide. The endpoint of this titration can be observed by measming the absorption at 326 nm. Initially, no change in the absorbance is observed vmtil all the arsenic(III) has been oxidized to arsenic(V). The absorbance then decreases to a minimmn at the end-point of the antimony titration, and then the absorbance increases again as excess titrant is added. 

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. 

A rapid method to determine the calcium content of lead alloys is a Hquid-metal titration using lead—antimony (1%) (9). The end point is indicated by a gray oxide film pattern on the surface of a sohdifted sample of the metal when observed at a 45° angle to a light source. The basis for the titration is the reaction between calcium and antimony. The percentage of calcium in the sample can be calculated from the amount of antimony used. If additional calcium is needed in the alloy, the melt is sweetened with a lead—calcium (1 wt %) master alloy. 

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 ... 

If the bulk of the iodate solution is added rapidly, atmospheric oxidation does not present a serious problem, but the method cannot be used in the presence of salts of antimony(III), copper(I), or iron(II). The solution, which should contain for example 0.15 g SnCl2,2H20 in 25 mL, is treated with 30mL of concentrated hydrochloric acid and 20 mL of water and is then titrated in the usual manner with standard potassium iodate solution. 

The introduction of reversible redox indicators for the determination of arsenic(III) and antimony(III) has considerably simplified the procedure those at present available include 1-naphthoflavone, and p-ethoxychrysoidine. The addition of a little tartaric acid or potassium sodium tartrate is recommended when antimony(III) is titrated with bromate in the presence of the reversible... 

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. 

Procedure. Place 45 mL of the supporting electrolyte in the cell and fill the isolated cathode compartment with the same solution to a level well above that in the cell. Pipette 5.00, 10.00, or 15.00 mL of the 0.01 M antimony solution into the cell and titrate coulometrically with a current of 40 milliamps. Stir the solution continuously by means of the magnetic stirrer and take e.m.f. readings of the Pt-S.C.E. electrode combination at suitable time intervals the readings may be somewhat erratic initially, but become steady and reproducible after about 3 minutes. Evaluate the end point of the titration from the graph of e.m.f. vs counter reading this shows a marked change of e.m.f. at the end point. If it proves difficult to locate the end point precisely, recourse may be made to the first- and second-differential plots. 

Dilute solutions of antimony(III) and arsenic(III) (ca 0.0005M) may be titrated with standard 0.002 M potassium bromate in a supporting electrolyte of 1M hydrochloric acid containing 0.05 M potassium bromide. The two electrodes are a rotating platinum micro-electrode and an S.C.E. the former is polarised to +0.2 volt. A reversed L-type of titration graph is obtained. 

Procedure. Pipette 25.0 mL of the antimony solution into the titration cell. Set the applied voltage at 0.2 volt vs S.C.E., and adjust the range of the micro-ammeter. Titrate in the usual manner, and calculate the concentration of the antimony solution. 

Procedure. Place 80 mL of the arsenic/antimony solution in the titration cell of the spectrophotometer. Titrate with standard bromate/bromide solution at 326 nm taking an absorbance reading at least every 0.2 mL. From the curve obtained calculate the concentration of arsenic and antimony in the solution. 

Electrical units 503, 519 Electrification due to wiping 77 Electro-analysis see Electrolysis and Electrogravimetry Electrochemical series 63 Electro-deposition completeness of, 507 Electrode potentials 60 change of during titration, 360 Nernst equation of, 60 reversible, 63 standard 60, (T) 62 Electrode reactions 505 Electrodeless discharge lamps 790 Electrodes antimony, 555 auxiliary, 538, 545 bimetallic, 575... 

Electrodes of the first kind have only limited application to titration in non-aqueous media a well-known example is the use of a silver electrode in the determination of sulphides and/or mercaptans in petroleum products by titration in methanol-benzene (1 1) with methanolic silver nitrate as titrant. As an indicator electrode of the second kind the antimony pH electrode (or antimony/antimony trioxide electrode) may be mentioned its standard potential value depends on proton solvation in the titration medium chosen cf., the equilibrium reaction on p. 46). 

The ready separation of the hexachloroantimonate salts of various cation radicals is possible owing to their insolubility in diethyl ether (or hexane) under conditions in which the reduced antimony(III) chloride is highly soluble. In the case of EA+ SbClg", the isolated product is quite pure as determined by iodometric titration. However in many other cases, the Lewis acid SbCl5 effects... 

The polyhedral boranes and carboranes discussed above may be regarded as boron clusters in which the single external orbital of each vertex atom helps to bind an external hydrogen or other monovalent atom or group. Post-transition main group elements are known to form clusters without external ligands bound to the vertex atoms. Such species are called bare metal clusters for convenience. Anionic bare metal clusters were first observed by Zintl and co-workers in the 1930s [2-5], The first evidence for anionic clusters of post-transition metals such as tin, lead, antimony, and bismuth was obtained by potentiometric titrations with alkali metals in liquid ammonia. Consequently, such anionic post-transition metal clusters are often called Zintl phases. 

The compound is digested with nitric acid and the solution is analyzed for antimony by AA or ICP spectrophotometry (see Antimony). To determine the chlorine content a measured amount of substance is heated at 300°C and the liberated CI2 is passed into an acidic solution of KI and analyzed by iodomet-ric titration using a standard solution of sodium thiosulfate or phenyl arsine oxide and starch indicator. 

For detn of purity of TeNCbz, Kaye(Ref 4) developed at PicArsn a method of titration, using dimethyl formamide as a medium and a soln Na methoxide as the titrant. As the end point could not be detd visually(using azo violet as indicator) due to the darkening of the TeNCbz sample in the vicinity of its end point, a potentiometric procedure was used, employing antimony and calomel electrodes. 

Antimony (v). In a series of papers, Lefebvre and Maria (21) have shown that the hydrolysis of Sb(OH)6" depends greatly on time at 25 °C. Spectrophotometry, pH titration curves, and iodometric titration curves were used in the studies. It is apparent that dodecantimonates are formed in several stages of protonation when HC1 is added to solutions of (CHa)4NSb(OH)( up to an H/Sb ratio of 0.7. However, the particular species formed depends upon the age of the solution. Solutions of the same composition but aged for different time intervals exhibit strikingly different rates of reaction with iodide and with hydroxide and have different extinction coefficients in the ultraviolet region. It is important to... 

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 ... 

Determine the mass of antimony in a solution which required a steady current of 23.2 milliamperes for 182 s to reach the end point in the above coulometric titration. 

Other examples of potentiometric titrations include acid-base titrations, in which an indicator electrode provides a response to hydronium ions, such as the glass electrode, quinhydione electrode, or antimony electrode. In precipitation and complexation titrations the indicator electrode should provide the response to the active species in the solution. Thus, during the titration of chloride ions by silver nitrate, a silver electrode is an effective indicator electrode. 

Four types of hydrous antimony oxide (antimonic acid), the amorphous (A-SbA), the glassy (G-SbA), the cubic (C-SbA), and the monoclinic (M-SbA) are known so far [138]. Both the A-SbA and G-SbA affect the selectivity sequence Li" < Na" < K" " < Rb+ < Cs", while the selectivity sequence of C-SbA is unusual with Li" " K+ < Cs < Rb" Na" " for micro amounts in acid media (Fig. 19). The degree of crystallinity of a-ZrP strongly influences its ion-exchange behavior as mentioned earlier. The pH versus base added plots for a-ZrP with different crystallinity are shown in Fig. 13. It is seen that each increase in acid concentration at a fixed reflux time is reflected in the shape of the curves. The titration curves with the most well-defined plateaus were obtained with the most highly crystalline samples [126]. 

For many purposes, hydrochloric acid is the most convenient titration medium, as it permits the use of Sn(II) chloride or a silver redactor as a selective reducing agent (Section 16-2). Petzold titrated small amounts of Fe(II) in the presence of arsenic, antimony, and Sn(II). Fe(II) can be titrated in the presence of V(TV) by using a silver redactor with 1 M hydrochloric acid and by making the solution 5 M in sulfuric add to prevent the oxidation of V(IV) at the ferroin end point. ... 

BRI/ROB] Britton, H. T. S., Robinson, R. A., The use of the antimony-antimonious oxide electrode in the determination of the concentration of hydrogen ions and in potentiometric titrations. The Prideaux-Ward universal buffer mixture, J. Chem. Soc., (1931), 458-473, Contains report of measurements by W. L. German. Cited on page 141. 

As stated earlier, the theoretical concentration profile is calculated on the assumption that the species of interest is not involved in a homogeneous reaction. With a pH probe such as the antimony-antimony oxide tip, this assumption is not valid because the buffer capacity of the solution significantly affects the concentration profile. For example, protons generated at the substrate react with the base form of the buffer and the concentration profile is no longer solely diffusion controlled. Similarly hydroxide anions produced by the substrate titrate the acid form of the buffer. A high-capacity buffer reestablishes the bulk conditions very close to the substrate, while a low-capacity buffer allows the concentration profile to extend far away from the substrate before returning to the bulk concentration. These effects were quantitatively predicted and theoretical pH profiles were found to agree with... 

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