Potassium permanganate solutions titrations with

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. 

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. 

Sample Problem A Write a balanced equation for the reaction shown in Figure 2.1 (on the previous page). A deep purple solution of potassium permanganate is titrated with a colorless solution of iron(II) sulfate and sulfuric acid. The products are iron(III) sulfate, manganese(II) sulfate, potassium sulfate, and water—all of which are colorless. 

In what way does a solution of hydrogen peroxide react with (a) chlorine water, (b) potassium permanganate solution, (c) potassium dichromate solution, (d) hydrogen sulphide 50 cm of an aqueous solution of hydrogen peroxide were treated with an excess of potassium iodide and dilute sulphuric acid the liberated iodine was titrated with 0.1 M sodium thiosulphate solution and 20.0 cm were required. Calculate the concentration of the hydrogen peroxide solution in g 1" ... 

An example of catalytic action is provided by the titration of oxalates with potassium permanganate solution referred to above. It is found that even though the oxalate solution is heated, the first few drops of permanganate solution are only slowly decolorised, but as more permanganate solution is added the decoloration becomes instantaneous. This is because the reaction between oxalate ions and permanganate ions is catalysed by the Mn2+ ions formed by the reduction of permanganate ions ... 

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). 

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 ferrous ion, c1+(aq), reacts with the permanganate ion, Mn04 (ag), in an acidic solution to produce the ferric ion, Fe3+(ag). A 6.893-gram sample of ore was mechanically crushed and then treated with concentrated hydrochloric acid, which oxidized all of the iron in the ore to the ferrous ion, Fe2+(aq). Next, the acid solution containing all of the ferrous ions was titrated with 0.100 M KMn04 solution. The end point was reached when 13.889 mL of the potassium permanganate solution was used. 

Procedure Weigh accurately about 0.5 g of ferric ammonium citrate and dissolve the sample in 15 ml DW. Add to it slowly 1 ml of sulphuric acid and warm gently to attain a yellow colouration so as to decompose the iron and ammonium citrate complex completely. Cool and add 0.1 N potassium permanganate solution dropwise from a burette to obtain a pink colour that persists for 5 seconds. To the resulting solution add hydrochloric acid 15 ml and potassium iodide 2.0 g, shake well and set aside for 3 minutes so that iodine may be liberated completely. Now, add 60 ml of water and titrate with 0.1 N sodium thiosulphate solution while shaking the contents continuously till a colourless end-point is achieved. 

Quantitative Determination. — Dissolve 1 gm. of powdered iron in about 50 cc. of dilute sulphuric acid, and dilute the solution to 100 cc. To 10 cc. of this solution add decinonnal potassium permanganate solution until the liquid has a slight red color, and when the liquid becomes decolorized, which may be effected, if necessary, by adding a few drops of alcohol, add 2 gm. of potassium iodide. Allow the mixture to stand one hour in a closed flask at 20° C., and then titrate with decinormal sodium thiosulphate. At least 17.5 cc. should be required to combine with the liberated iodine. 

Quantitative Determination. — Dissolve 1 gm. of ferrous ammonium sulphate in 50 cc. of well-boiled and cooled water, add 10 cc. of dilute sulphuric acid, and titrate with decinormal potassium permanganate solution. 

Estimation of Vanadium.1—Volumetric Methods.—The most convenient and the usual method for the estimation of vanadium is a volumetric process. The vanadium is first obtained in acid solution as vanadate, and reduced to the tetravalent state by one of several reducing agents which are available. The solution is then titrated in the presence of sulphuric acid with hot potassium permanganate solution, which quantitatively oxidises the lower vanadium salt to the vanadate. Using sulphur dioxide to effect the reduction, the following reactions take place —... 

The hydroxylamine hydrochloride used was the crude material prepared as described in Org. Syn. 3, 61. Preliminary experiments showed that this reagent must be present in considerable excess. Equally good results were obtained by using a solution of crude hydroxylamine sulfate which also contained sodium sulfate and ammonium sulfate with a little excess sulfuric acid. The hydroxylamine content was determined in this solution by titration with potassium permanganate solution. When this crude solution is used, the addition of sodium sulfate is not always necessary. 

By adding sulphuric acid to a portion of the clear solution and estimating the excess of potassium ferrocyanide by titration with permanganate, the method may be made a convenient one for the estimation of zinc.13... 

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. 

An accurately weighed portion of sodium oxalate (0.1550g) was dissolved in dilute sulphuric acid (250 mL). Whilst maintaining the temperature of the solution above 70 °C, it was titrated to equivalence with potassium permanganate solution (18.5 mL). What is the molarity of potassium permanganate ... 

Recently, Hiller and Pacsu have shown that accurate results may be obtained in the absence of sodium chloride by a direct alkali titration of the carboxyl groups in purified cotton. The carboxyl group content found was 0.02%, but after oxidation with potassium permanganate solution, 0.126% was found. From these data it may be seen that both carboxyl and aldehydic groups are present in the original cellulosic... 

In llraidy s modification, which is stated to give more consistent results, 2 5 g. of very finely divided air-dry cotton is treated with a mixture of 5 c.c. of 10 per cent, copper sulphate (cryst.) and 95 c.c. of an almost saturatcd solution of sodium carbonate and bicarbonate g crystals and 50 g. bicarbonate made up to 1 litre). The cotton is immersed by means of a rod and the air bubbles are allowed to escape the flask is then surrounded with boiling water for exactly three hours. The contents arc filtered off on an asbestos filter and washed first with dilute sodium carbonate solution and then with water. Then the residual cuprous oxide is dissolved by treatment with a solution containing 100 g. of iron alum and 140 g. of concentrated sulphuric acid per litre. Two such treatments usually suffice. The fitter is tben washed with 2 Af-sulphuric acid the combined filtrate and washings arc titrated with A /25 potassium permanganate solution. According to Brissaud the test is affected by air. 

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