Standardize a solution of potassium manganate(VII) by an iron (II) salt (ammonium iron (II) sulphate) Introduction 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. If the oxidation number of an atom increases as you go from the left side to the right side if an equation, oxidation has occurred (electrons have been lost); if the oxidation number decreases, reduction has occurred (electrons have been gained). MnO4? + 8 H+ + 5e? Mn+? + 4 H2O (1) In the above reduction half-reaction, manganese has undergone a decrease in oxidation number from +7 to +2. In the following oxidation half-reaction, each iron atom has undergone an increase in oxidation number from +2 to +3. Fe+? > Fe+? + e? (2) Oxidation must occur along with reduction. These reactions are called redox (reduction/oxidation ) reactions. The number of electrons lost and gained in the half reactions must be equal. The overall redox reaction becomes: MnO4? + 5 Fe+? + 8H+ > Mn+? + 5 Fe+? 4H2O (3) Potassium permanganate is widely used as an oxidizing agent in volumetric analysis. Since the MnO4 ion is a deep pink-violet colour and the Mn2+ ion is nearly colourless, the end point in titrations using KMnO4 can be taken as the first pink colour that persists in the solution. In titration , permanganate solution is put in the burette and is run down to an acidified solution of reducing agent, e. g.. ammonium iron(II) sulphate solution. In this experiment, KMnO4 will be used to determine the percentage of Fe2+ in an unknown solid sample dissolved in water.
The permanganate oxidation of Fe2+ to Fe3+ is carried out in an acidic solution to prevent the air oxidation of Fe2+. A potassium permanganate solution will be standardized by titrating it with a known mass of Mohr’s salt, ferrous ammonium sulphate hexahydrate or Fe(NH4)2(SO4)2·6H2O. (Mohr’s salt fulfils the requirements of a primary standard. It is easily obtained in pure form, it is stable to oxidation when dry and is not hygroscopic. http://faculty. ccri. edu/eterezakis/1100%20Exp%205,%20Iron%20Analysis%20by%20Redox%20Titration%20_egt_. pdf http://www. mrteverett. om/Chemistry/labs/Chem%201A%20-%20Lab%20-%20Titration%20%28Redox%29. pdf Objectives To prepare and standardize a solution of an oxidizing agent,potassium manganate(VII) by titrating it with standard solution of a reducing agent,ammonium iron (II) sulphate. Then use the standardized to determine the concentration of a sample of unknown concentration. Materials Ammonium iron (II) sulphate crystals Potassium manganate (VII) solution Distilled water 1. 0M sulphuric acid Apparatus Beakers 250cm? volumetric flask Conical flask Burette Pipette Electronic weighing machine Methods