Potassium Manganate 6n2m5w

Potassium manganate(VII) solution cannot be accurately prepared by weighing the salt, for several reasons:  it is not commercially obtainable in a high state of purity;  it readily oxidises traces of organic materials (e.g. dust) which find their way into the solution;  the potential for the MnO4-/MnO2 couple is such that it slowly oxidises solvent water - this is why potassium manganate(VII) solution gradually deposit manganese(IV) oxide on storage. The solution must therefore be standardised against a primary standard. Such a compound has the following characteristics:  it can be obtained commercially in high purity;  it is stable in solution;  it does not absorb water or carbon dioxide from the atmosphere nor vaporise whilst being weighed;  it can be dried readily in an oven or by stronger heating without decomposition. A suitable primary standard for the standardisation of potassium manganate(VII) solution is sodium ethanedioate, Na2C2O4. The reaction is 2MnO4- + 5C2O42- + 16H+  2Mn2+ + 10CO2 + 8H2O Objective: 1. To standardize a solution of potassium manganate(VII) by an iron(II) salt (ammonium iron(II) sulphate). Introduction: In this experiment, it is a redox titration method to standardize a solution of potassium manganate(VII) by an iron(II) salt (ammonium iron(II) sulphate). So, the word of redox is related to the oxidation and reduction. Oxidation numbers describe the number of electrons the atom will gain or lose during a reaction. Each atom in an equation can be assigned an oxidation number according to certain rules. Oxidation occurs when the oxidation number of an atom increases while reduction occurs when the oxidation number decreases. Potassium manganate (VII) (KMnO4) solution is standardised by titration against the ammonium iron(II) sulphate, FeSO4 .(NH4)2SO4.6H2O. Potassium manganate is widely used as an oxidizing agent in volumetric analysis. While the ammonium iron(II) sulphate is

used as a primary standard to standardize the KMnO4 solution. In this experiment, ammonium iron(II) sulphate crystals are the stable compound that remain as solid in room temperature. Hence, the ammonium(II) sulphate solution is obtained by dissolving into the sulphuric acid, preferably oxygen. During the titration process, the ammonium iron(II) sulphate ionises into iron(II), sulphate and ammonium ions. But, only the iron(II) ions (Fe2+) are oxidized by the managanate(VII) ions (MnO4-). The following equation represents the reaction: MnO4- + 8H+ + 5Fe2+ â Mn2+ + 5Fe3+ + 4H2O Throughout the experiment, there is no additional of indicator. Manganate(VII) is an intense dark purple colour. But, there is a colour change of manganate(VII) to Mn+2, which is from dark purple to light pink. At the end of the experiment, the colour of the potassium manganate disappears as it reacts with the iron(II) ions. This is because all the Fe2+ ions are fully reacted, whereas the extra drop of potassium manganate solution will make the titration mixture turn pink. Results: Description Mass (g) Mass of weighing bottle + crystals 23.35 Mass of weighing bottles 13.65 Mass of ammonium iron(II) sulphate