Titration potassium manganate

Excess standard acid is added, and the excess (after disappearance of the solid oxide) is estimated by titration with standard potassium manganate(VII). 

As part of an experiment to determine the value of x in the formula for iron(ll) sulfate crystals (FeSO HjO) a student titrated a solution of these crystals with 0.0200 mol/dm- potassium manganate(VII) (solution A). 

Why is it not necessary to have an indicator present in potassium manganate(Vll) titrations ... 

A solution of hydroxylamine hydrochloride contains 0.1240g of NH OH HCl. On boiling, it is oxidised by an excess of acidified iron(III) sulphate. The iron salt formed is titrated against potassium manganate(VII) solution of concentration 0.0160 mol dm" . A volume of 44.6 cm of the oxidant is required. 

The most stable oxidation state is +3, which is yellow, but +2 (green) and +6 (easily reduced) also exist. Solutions of iron(II) ions give a green precipitate with sodium hydroxide solution, whereas iron(III) ions give a brown precipitate. The concentration of iron(II) ions can be estimated in acid solution by titration with standard potassium manganate(VII) solution. Iron(III) ions must first be reduced to iron(II) ions with sulfur(IV) oxide (sulfur dioxide). 

Potassium manganate(vii), KMn04, oxidizes potassium iodide, Kl, to iodine, I2. The iodine liberated is titrated with aqueous sodium thiosulfate, Na2S203. 

A solution of potassium manganate(vii) can be standardized by titration under suitable conditions with a solution of arsenic(iii) oxide, AS2O3. 5 moles of arsenic(iii) oxide are oxidized by 4 moles of manganate(vii) ions. Calculate the oxidation state to which the manganate (vii) is reduced. 

A piece of steel (an alloy of iron and carbon) of mass 0.200 g reacts with dilute sulfuric acid. The resulting solution requires 34.00cm of 0.0200 mol dm potassium manganate(vii) in acidic solution in a titration. Determine the percentage by mass of iron in the steel. 

A 2.41 g nail made from an alloy containing iron is dissolved in lOO.OOcm of acid. The solution formed contains iron(ii) ions, Fe +(aq). lO.OOcm portions of this solution are titrated with potassium manganate(vii) solution of 0.02 moldm g.gOcm of potassium manganate(vii) solution were needed to react with the solution containing the iron. Calculate the percentage of iron by mass in the nail. 

The potassium manganate(Vii) solution is titrated against the solution containing Fe "(aq) in the conical flask. 

You can achieve a more accurate result for the mass of Fe + in a solution by using dichromate(VI) ions, Cr O (aq), to oxidise it in a titration. This is because compounds such as potassium dichromate(VI) can be prepared to a higher degree of purity than potassium manganate(VII). In a titration with Fe +(aq) and dichromate(VI) we need an indicator of the end-point that will be oxidised as soon as the Fe +(aq) has all reacted. 

A solution of ethanedioic acid (with sulfuric acid added) can be used in titrations to standardise a solution of potassium manganate(VII). As with methanoic acid, the oxidation results in the formation of carbon dioxide and water. The solid ethanedioic acid can be weighed out accurately to make a standard solution of known concentration. This is warmed in a conical flask and the potassium manganate(VII) solution to be standardised is run in from a burette. The end-point of the titration is identified when the addition of a drop of the purple manganate(VII) solution turns the solution pink. This happens when all the ethanedioic acid has been oxidised. 

The manganate ion is not reduced by bromide ion but is reduced slowly by iodide ion and quickly by vanadyl(IV) or hexacyano-ferrate(II) ions. When the latter two ions are used as reductants, especially with the potassium complex, green products are obtained rapidly and in high yield. The green species is unstable in solution and is apparently in equilibrium with the reactants. With potassium salts, the solubility of the product is low, and the reaction is driven to completion. Potentiometric titrations show that a one-electron reduction occurs to produce the green species, which has been characterized by analysis and optical and e.s.r. spectroscopy. It is a mixed-valence species similar to the heteropoly blues of molybdenum and tungsten. E.s.r. spectra suggest that the extra electron is fairly well trapped on a specific vanadium atom, and the complex is therefore a class II mixed-valence species.8... 

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