CLEAPSS Recipe Book 73 Potassium manganate(VII) Also known as potassium permanganate. Solutions must be acidic. Solutions are safer made up in dilute sulfuric(VI) acid rather than adding concentrated sulfuric(VI) acid at a later stage. Solutions do not keep well unless the container is scrupulously clean. They slowly reacts with water, forming manganese(IV) oxide which badly stains glass and plastic equipment. Solutions are best kept in dark bottles, shielded from light. Light increases the rate of decomposition and staining of equipment. Equipment can be cleaned by filling the bottle either with 1 M sulfuric(VI) acid with a small amount of hydrogen peroxide solution (20 or 100 vol) or, if this does not work, add 2 M hydrochloric acid and leave it for several hours (or days) in a fume cupboard. Use a 0.002 M solution for carrying out tests for unsaturation in alkenes. It is not possible to make a 1 M solution. Molar mass: 158.03 g mol-1 Formula: KmnO4 General Hazards Solubility: 6 g per 100 ml See Hazcard 81. Mass (g) of solid to be used Concentration Conc of acid required for dilution 0.002 M 0.1 M 0.02 M 0.1 M Saturated 0.1 M 1M 1M Volume (ml) of solution required 500 1000 2500 Ten-fold dilution of the 0.02 M solution with 0.1 M sulphuric(VI) acid 1.58 3.16 7.90 7.90 15.80 39.51 32 64 160 Hazard warning label IRRITANT IRRITANT Procedure • Wear eye protection. • It would be advisable to wear gloves as the chemical stains the skin brown. • Measure out the indicated quantity of potassium manganate(VII). • Add the solid to about two thirds of the final volume of the suggested dilute sulfuric(VI) acid in a beaker or laboratory jug. • Stir to dissolve. It is better not to heat but dissolving can take some time, and it is difficult to see when the solid has all dissolved. • Pour the solution from the beaker into an appropriate measuring cylinder or laboratory jug and add dilute sulfuric(VI) acid to the required level. • Pour into a labelled bottle. © CLEAPSS 2011 81