Potassium permanganate solution standardization

Potassium permanganate solution, standardized 0.1000 0.0005 N KMn04 sodium thiosulfate solution, approximately 0.2 N Na2S203, normality known with an accuracy of 0.0005 N 1.0 N potassium iodide solution 4N sulfuric acid 0.2% starch indicator solution. 

Calculation. It is evident from the equation given above that if the weight of arsenic(III) oxide is divided by the number of millilitres of potassium permanganate solution to which it is equivalent, as found by titration, we have the weight of primary standard equivalent to 1 mL of the permanganate solution. 

If a solution of a nitrite is titrated in the ordinary way with potassium permanganate, poor results are obtained, because the nitrite solution has first to be acidified with dilute sulphuric acid. Nitrous acid is liberated, which being volatile and unstable, is partially lost. If, however, a measured volume of standard potassium permanganate solution, acidified with dilute sulphuric acid, is treated with the nitrite solution, added from a burette, until the permanganate is just decolorised, results accurate to 0.5-1 per cent may be obtained. This is due to the fact that nitrous acid does not react instantaneously with the permanganate. This method may be used to determine the purity of commercial potassium nitrite. 

Discussion. Alkali persulphates (peroxydisulphates) can readily be evaluated by adding to their solutions a known excess of an acidified iron(II) salt solution, and determining the excess of iron(II) by titration with standard potassium permanganate solution. 

The excess of oxalic acid is titrated with standard potassium permanganate solution. 

Procedure A. Prepare an approximately 0.1 JVf solution of ammonium iron(II) sulphate by dissolving about 9.8 g of the solid in 200 mL of sulphuric acid (0.5M) in a 250 mL graduated flask, and then making up to the mark with freshly boiled and cooled distilled water. Standardise the solution by titrating 25 mL portions with standard potassium permanganate solution (0.02M) after the addition of 25 mL sulphuric acid (0.5JVf). 

Procedure B. Prepare an approximately 0.05 M solution of oxalic acid by dissolving about 1.6 g of the compound and making up to 250 mL in a graduated flask. Standardise the solution with standard (0.02M) potassium permanganate solution using the procedure described in Section 10.94 (Method B). 

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... 

With the exception of iron(II) and uranium(IV), the reduced solutions are extremely unstable and readily re-oxidise upon exposure to air. They are best stabilised in a five-fold excess of a solution of 150g of ammonium iron(III) sulphate and 150 mL of concentrated sulphuric acid per litre [approximately 0.3M with respect to iron] contained in the filter flask. The iron(II) formed is then titrated with a standard solution of a suitable oxidising agent. Titanium and chromium are completely oxidised and produce an equivalent amount of iron(II) sulphate molybdenum is re-oxidised to the Mo(V) (red) stage, which is fairly stable in air, and complete oxidation is effected by the permanganate, but the net result is the same, viz. Mo(III)- Mo(VI) vanadium is re-oxidised to the V(IV), condition, which is stable in air, and the final oxidation is completed by slow titration with potassium permanganate solution or with cerium(IV) sulphate solution. 

Procedure. Dissolve a weighed portion of the substance in which the amount of iron is to be determined in a suitable acid, and evaporate nearly to dryness to expel excess of acid. Dilute slightly with water, oxidise the iron to the iron(III) state with dilute potassium permanganate solution or with a little bromine water, and make up the liquid to 500 mL or other suitable volume. Take 40 mL of this solution and place in a 50 mL graduated flask, add 5 mL of the thiocyanate solution and 3 mL of AM nitric acid. Add de-ionised water to dilute to the mark. Prepare a blank using the same quantities of reagents. Measure the absorbance of the sample solution in a spectrophotometer at 480 nm (blue-green filter). Determine the concentration of this solution by comparison with values on a reference curve obtained in the same way from different concentrations of the standard iron solution. 

Use Appendix 2B to determine whether an acidic-potassium permanganate solution can oxidize (a) chloride ions to chlorine and (b) mercury metal to mercurv(I) ions under standard conditions. 

Theory The standardization of potassium permanganate solution is based upon the following equations ... 

In an experiment to determine the percentage by mass of manganese in a steel paper clip, it is necessary to prepare various concentrations of standard potassium permanganate solutions. You will learn more about this experiment on p. 88. A standard 0 0010 mol h solution of potassium permanganate is often used as a stock solution in this experiment. Dilutions of the stock solution are prepared by accurately transferring a known volume of the stock solution, using a pipette or a burette, into a volumetric flask (standard flask). The flask is then carefully filled to the graduation mark with deionised water. 

Iodine in aqueous solution may be measured quantitatively by acidifying the solution, diluting it, and titrating against a standard solution of sodium thiosulfate, sodium arsenite or phenyl arsine oxide using starch indicator. The blue color of the starch decolorizes at the end point. The indicator must be added towards the end of titration when the color of the solution turns pale yellow. Prior to titration, iodine in the dilute acidic solution is oxidized to iodate by adding bromine water or potassium permanganate solution. Excess potassium iodide is then added. The liberated iodine is then titrated as above. 

This ferrous sulphate solution is standard toed against semi-normal potassium permanganate solution on t.ho same day, using the same pipette. 

Oxidizing reagents such as tetravalent cerium or potassium permanganate solutions may be standardized by oxalic acid, sodium oxalate, or potassium iodide. The reactions of Ce4+ and permanganate ions with oxalic acid in acid medium are given below ... 

A solution of potassium permanganate was standardized against sodium oxalate (Na C ) primary standard. A 50.0 mL 0.01 MNa2C204 standard solution required 37.8 mL KMn04 solution. Determine the strength (molarity) of KMn04 solution. 

Potassium pentachloronitrido-osmate(VI), 6 206 Potassium permanganate, solution of, standardization of, for determination of average atomic weight of rare earth elements in oxalates, 2 60, 61 Potassium pyrosulfite, 2 166 and its f-hydrate, 2 165, 167 Potassium rare earth sulfates, 2 47 Potassium selenocyanate, 2 186 Potassium sulfites, KHSO , in solution, 2 167... 

Methanol Prepare a Sample Solution by diluting 10 mL of sample to 100 mL with water. Prepare a Standard Solution in water containing 40 p.g of methanol in each milliliter. Add 0.2 mL of 10% phosphoric acid and 0.25 mL of 1 20 potassium permanganate solution to 1 mL of each solution. Allow the mixtures to stand for 15 min, then add 0.3 mL of 1 10 sodium bisulfite solution to each, and shake until colorless. Slowly add 5 mL of ice-cold 80% sulfuric acid, keeping the mixtures cold during the addition. Add 0.1 mL of 1 100 chromotropic acid solution, mix, and digest on a steam bath for 20 min. 

Standard Preparations Dissolve 338.5 mg of mercuric chloride, in about 200 mL of water in a 250-mL volumetric flask, add 14 mL of 1 2 sulfuric acid, dilute to volume with water, and mix. Pipet 10.0 mL of this solution into a 1000-mL volumetric flask containing about 800 mL of water and 56 mL of 1 2 sulfuric acid, dilute to volume with water, and mix. Pipet 10.0 mL of the second solution into a second 1000-mL volumetric flask containing 800 mL of water and 56 mL of 1 2 sulfuric acid, dilute to volume with water, and mix. Each milliliter of this diluted stock solution contains 0.1 pig of mercury. Pipet 1.25, 2.50, 5.00, 7.50, and 10.00 mL of the last solution (equivalent to 0.125, 0.250, 0.500, 0.750, and 1.00 ptg of mercury, respectively) into five separate 150-mL beakers. Add 25 mL of aqua regia to each beaker, cover with watch glasses, heat just to boiling, simmer for about 5 min, and cool to room temperature. Transfer the solutions into separate 250-mL volumetric flasks, dilute to volume with water, and mix. Transfer a 50.0-mL aliquot from each solution into five separate 150-mL beakers, and add 1.0 mL of 1 5 sulfuric acid and 1.0 mL of a filtered solution of 1 25 potassium permanganate solution to each. Heat the solutions just to boiling, simmer for about 5 min, and cool. 

Procedure Transfer 100 mL of Standard Solution to a 300-mL mercury analysis reaction vessel, add 2 drops of a 1 20 potassium permanganate solution, and mix (the solution should be purple add additional permanganate solution, drop-wise, if necessary). Add 5 mL of 11 A nitric acid, stir, and allow to stand for not less than 15 s. Add 5 mL of 18 A sulfuric acid, stir, and allow to stand for not less than 45 s. Add 5 mL of a 3 200 hydroxylamine hydrochloride solution, stir, and allow to stand until the solution turns light yellow or colorless. Add 5 mL of a 1 10 stannous chloride solution, immediately insert the aerator connected to an air pump, and determine the maximum absorbance of the treated Standard Solution at the mercury resonance line of 253.65 nm, with a suitable atomic absorption spectrophotometer equipped with a mercury hollow-cathode lamp and an absorption cell that permits the flameless detection of mercury. 

Standard Preparation Prepare a solution containing 1 pig of mercury per milliliter as directed in Standard Preparation under Mercury Limit Test, Appendix MB. Transfer 1.0 mL of the solution into a 50-mL beaker, and add 20 mL of water, 1 mL of a 1 5 sulfuric acid solution, and 1 mL of a 1 25 potassium permanganate solution. Cover the beaker with a watch glass, boil for a few seconds, and cool. 

The APDC—MIBK extraction system is widely used to determine a variety of metals in water. In both the U.K. [6, 7] and the U.S.A. [8] it is the standard method for the determination of lead and cadmium in water. It is also used as a standard method [8] in the determination of hexavalent chromium. In order to determine total chromium, trivalent chromium is oxidised to hexavalent chromium by bringing the sample to the boil and adding sufficient potassium permanganate solution (0.1 N) dropwise to give a persistent pink colour while the solution is boiled for 10 min. 

Method. Transfer 100 ml of sample to a 300 ml glass flask. Add 5 ml of sulphuric acid and 2.5 ml of nitric acid, mixing after each addition. Add 15 ml of potassium permanganate solution to each sample bottle. Shake and add additional portions of permanganate solution until the purple colour persists for at least 15 min. Add 8 ml of potassium persulphate to each bottle and heat for two hours in a water bath at 95° C. Cool and add 6 ml of sodium chloride—hydroxylamine sulphate solution to reduce the excess of oxidant prior to analysis. Standards and blanks should be treated in the same way as samples. 

A potassium permanganate solution is standardized by dissolving 0.9234 g sodium oxalate in dilute sulfuric acid and then titrating with the potassium permanganate solution. The principal products of the reaction are man-ganese(II) ion and carbon dioxide gas. The titration requires 18.55 mL of the potassium permanganate solution to reach the endpoint, which is indicated by the first permanent, but barely perceptible, pink color of the permanganate ion. 

Example 2. A solution of potassium permanganate was standardized by determining the volume necessary to oxidize an acidic solution of ferrous iron. It was found that 0.1135 g of pure iron wire, when dissolved in acid and converted to the ferrous salt (containing ferrous ions, Fe++), required 23.85 ml of the standard solution of potassium permanganate to oxidize it to ferric ion, Fe+ + +. It was also found that 0.2281 g of iron ore, when converted to a solution of ferrous iroif in acid, required 22.35 ml of the standard permanganate solution to reach the end point. What is the normality of the permanganate solution, and what is the percentage of iron in the ore ... 

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