Titrations with potassium bromate

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). 

Sandri (15) tested three titration methods with good results. One was titration with potassium bromate in the presence of potassium bromide and hydrochloric acid, using a starch-iodine end-point. Another was addition of excess periodic acid-potassium iodide with sodium... 

Titrations with Potassium Bromate, and (iii) Titrations with Potassium Iodate. 

Primary-standard potassium bromate is available from commercial sources and can be used directly to prepare standard solutions that are stable indefinitely. Direct titrations with potassium bromate are relatively few. Instead, the reagent is a convenient and widely used stable source of bromine. In this application, an unmeasured excess of potassium bromide is added to an acidic solution of the analyte. On introduction of a measured volume of standard potassium bromate, a stoichiometric quantity of bromine is produced. 

Destroy the organic matter in 0 2 to 0-4 g by heating with small quantities of an oxidising mixture of strong sulphuric, nitric and perchloric acids. When a colourless liquid results and fumes of sulphuric acid appear, cool, add 0 25 g of hydrazine sulphate and heat the liquid for ten minutes to reduce the arsenic to the trivalent form and to decompose any excess of reducing agent. Add 20 ml of water and cool add 0-1 to 0 2 g of potassium bromide and titrate with potassium bromate solution until a faint yellow colour of free bromine is obtained. 1 ml 0 1 N bromate = 0 003746 g. As. 

Ganescu et al. used thiocyanato Cr(III)-complexes in the titrimetric and spectrophotometric determination of dipyridamole [16]. For titrimetric analysis of the drug (1.36-27.2 mg), sample solutions (25-50 mL) were acidified with hydrochloric acid and treated with excess of a 3% solution of ammonium dianilinetetrakis (thiocyanato) chromium (III) in aqueous 25% ethanol. The red-violet precipitate was collected and washed, decomposed with NaOH, and the mixture again acidified. The liberated thiocyanate was titrated with potassium permanganate, potassium bromate, or potassium iodate. 

For the determination of phenoxy groups in phenoxyphenylsilanes, bomb fusion with potassium hydroxide is carried out and an aliquot of an aqueous solution of the melt is analysed for phenoxide by titration with potassium bromide-potassium bromate solution. Phenylphenoxy groups in phenyl(phenylphenoxy)silanes are similarly determined, but the melt is dissolved in anhydrous acetic acid138. 

Another important amperometric titrant is bromine solution, which undergoes stoichiometric oxidation-reduction reactions with many substances such as As(III), Sb(III), ammonium salts, and others. Often the titration involves adding an excess of KBr to an acidified solution of the substance to be oxidized and then titrating it with potassium bromate solution. Bromine is thereby generated in situ. 

The bromine index can be measured by electrometric and coulomelric titration. In the electrometric titration method, a sample is titrated with bromide-bromate solution (0.1 N solution of mixture of potassium bromide and potassium bromate) until the end-point increase in potential remains steady for 30 s. In coulometric titration, a potassium bromide solution is used to titrate the solvent until the bromine concentration increases because it is no longer being consumed by the unsaturation of the solvent. ... 

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... 

To determine the purity of a sample of arsenic(III) oxide follow the general procedure outlined in Section 10.127 but when the 25 mL sample of solution is being prepared for titration, add 25 mL water, 15 mL of concentrated hydrochloric acid and then two drops of indicator solution (xylidine ponceau or naphthalene black 12B see Section 10.125). Titrate slowly with the standard 0.02M potassium bromate with constant swirling of the solution. As the end point approaches, add the bromate solution dropwise with intervals of 2-3 seconds between the drops until the solution is colourless or very pale yellow. If the colour of the indicator fades, add another drop of indicator solution. (The immediate discharge of the colour indicates that the equivalence point has been passed and the titration is of little value.)... 

The hydroxylamine solution is treated with a measured volume of 0.02M potassium bromate so as to give 10-30 mL excess, followed by 40 mL of 5M hydrochloric acid. After 15 minutes the excess of bromate is determined by the addition of potassium iodide solution and titration with standard Q.1M sodium thiosulphate (compare Section 10.134). 

The concentration of the potassium bromate can be checked by the following method pipette 25 mL of the solution into a 250 mL conical flask, add 2.5 g of potassium iodide and 5 mL of 3M sulphuric acid. Titrate the liberated iodine with standard 0.1M sodium thiosulphate (Section 10.114) until the solution is faintly yellow- Add 5 mL of starch indicator solution and continue the titration until the blue colour disappears. 

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. 

Discussion. In acid solution arsenic(III) can be oxidised to arsenic(V) and antimony(III) to antimony(V) by the well-established titration with a solution of potassium bromate and potassium bromide (Section 10.133). The end point for such determinations is usually observed indirectly, and very good results have been obtained by the spectrophotometric method of Sweetser and Bricker.23 No change in absorbance at 326 nm is obtained until all the arsenic)III) has been oxidised, the absorbance then decreases to a minimum at the antimony(III) end point at which it rises again as excess titrant is added. 

The sample is acidified with sulfuric acid. The bromide content is then determined by the volumetric procedure described by Kolthoff and Yutzy [21 ]. In this procedure the buffered sample is treated with excess sodium hypochlorite to oxidise bromide to bromate. Excess hypochlorite is then destroyed by addition of sodium formate. Acidification of the test solution with sulfuric acid followed by addition of excess potassium iodide liberates an amount of iodine equivalent to the bromate (i.e., the original bromide) content of the sample. The liberated iodine is titrated with standard sodium thiosulfate. 

Procedure Transfer an accurately measured volume of about 30.0 ml of 0.1 N potassium bromate solution into a 250 ml iodine flask. Add to it 3.0 g potassium iodide, followed by 3.0 ml of potassium iodide, followed by 3.0 ml of hydrochloric acid. Mix the contents thoroughly and allow it to stand for 5 minutes with its stopper in position. Titrate the liberated iodine with previously standardized 0.1 N sodium thiosulphate, using 3.0 ml of freshly prepared starch solution as an indicator at the end-point. Carry out a blank run using the same quantities of the reagents and incorporate the necessary corrections, if any. Each ml of 0.1 N sodium thiosulphate is equivalent to 0.002784 g of KBr03. 

Procedure Weigh accurately 0.5 g of phenol and dissolve in sufficient water to produce 500 ml in a volumetric flask. Mix 25.0 ml of this solution with 25.0 ml of 0.1 N potassium bromate in a 250 ml iodine flask and add to it 1 g of powdered KI and 10.0 ml of dilute hydrochloric acid. Moisten the glass stopper with a few drops of KI solution and place it in position. Set it aside in a dark place for 20 minutes while shaking the contents frequently in between. Add to it 10 ml of KI solution, shake the contents thoroughly and allow it to stand in the dark for a further duration of 5 minutes. Wash the stopper and neck of the flask carefully with DW, add 10 ml chloroform and titrate with the liberated iodine with 0.1 N sodium thiosulphate using freshly prepared starch as an indicator. Carry out a blank titration simultaneously and incorporate any necessary correction, if required. Each ml of 0.1 N potassium bromate is equivalent to 0.001569 g of C6H60. 

A few other pharmaceutical substances may also be assayed by titrating with 0.1 N potassium bromate as indicated in Table 13.2. 

A sample of phenol glycerol injection was dilutee with water and an aliquot was taken and reacted with excess bromine generated from potassium bromide and potassium bromate solutions. The excess bromine remaining after reaction was reacted with potassium iodide and the liberated iodine was titrated with sodium thiosulphate. A blank titration was carried out where the same quantity of bromine was generated as was used in the titration of the diluted injection, potassium iodide was then added and the liberated iodine was titrated with sodium thiosulphate. From the following data calculate the percentage of w/v of the phenol in the injection. 

A sample (approximately 0.2 g.) is weighed accurately and dissolved in 25 ml. of water then 25 ml. of 0.1 N hydrochloric acid and 0.2 g. of potassium bromide are added. The solution is titrated with 0.017 M potassium bromate until a permanent yellow color is produced. Potassium iodide (0.1 g.) is added, and the solution is backtitrated to a starch end point with 0.1 N sodium thiosulfate. The blue color returns in about a minute since the high acidity promotes air oxidation of excess iodide. The accuracy is only slightly less if the appearance of a faint yellow bromine color is taken as the end point. One mole of potassium bromate is equivalent to 3 of sodium /8-styrenesul-fonate. 

The amount of oil in a sample is determined by Scott oil analysis (AOAC, 1990e). This is a bromination reaction previously used to determine the number of fatty acid double bonds. This titration method quantifies the recoverable oil in fruits and fruit products based on the release of Br2 and the formation of limonene tetrabromide (Braddock, 1999). Figure Gl.5.3 illustrates the chemical reaction for the bromination of limonene. Other monoterpenes (a-pinene and citral) also react however, the method is accurate to within 10 ppm limonene (Scott and Valdhuis, 1966). For this procedure, limonene is co-distilled with isopropanol and titrated with a potassium bromide/bromate solution. 

Preparation of Nj5 Bromate Solution.—5-567 gms. (1/30 mol.) of potassium bromate are dissolved in water to 1,000 c.cs. 25 c.cs. are withdrawn, diluted to 200 c.cs. with water, 3—5 gms. of potassium bromide (free from bromate), 3—5 gms. potassium iodide (free from iodate) and 5 c.cs. cone, hydrochloric acid (free from chlorine or iron) added. The liberated iodine is titrated with thiosulphate in the usual way, and the bromine equivalent of the bromate solution thus obtained. 

Arsenic may be determined iodometricaQy. A dried sample of 150-200 mg. is mixed with 7 ml. of 15 N nitric acid and the solution boiled gently for 5-10 minutes. Three milliliters of 2 AT sodium bromate is then added and the mixture evaporated gently to dryness. The residue is taken up in 150 ml. of 4 M hydrochloric acid in an iodine flask then 1 g. of sodium hydrogen carbonate is cautiously mixed in to displace the air, followed by 1 g. of potassium iodide. The flask is then stoppered and allowed to stand 5 minutes. The contents are rapidly titrated with 0.05 N sodium thiosulfate to the disappearance of the iodine color. 

Bromine, 0.1 N (7.990 g Br per 1000 mL) Dissolve 3 g of potassium bromate (KBr03) and 15 g of potassium bromide (KBr) in sufficient water to make 1000 mL, and standardize the solution as follows Transfer about 25 mL of the solution, accurately measured, into a 500-mL iodine flask, and dilute with 120 mL of water. Add 5 mL of hydrochloric acid, stopper the flask, and shake it gently. Then add 5 mL of Potassium Iodide TS, restopper, shake the mixture, allow it to stand for 5 min, and titrate the liberated iodine with 0.1 N Sodium Thiosulfate, adding Starch TS near the end of the titration. Calculate the normality. Store this solution in dark, amber-colored, glass-stoppered bottles. 

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