Preparation of Potassium Peroxodisulphate

On electrolysing a cool solution of potassium hydrogen sulphate, the discharged anions combine to form peroxodisulphate (persulphate) ions. 

Prepare a saturated solution of potassium hydrogen sulphate, cool in ice for 30 minutes and quickly filter, collecting the filtrate in a receiver cooled in ice. Measure 20 cm of the cooled filtered solution into a small beaker cooled in ice. Suspend in the solution a coil of platinum wire as anode and another coiled platinum wire as cathode. Connect the electrodes to a 6V dc supply in a circuit containing a variable resistance, an ammeter in series and a voltmeter in parallel to the electrolytic cell. Adjust the position of the electrodes so that a current of 0.4A passes through the solution. Electrolyse for 60 minutes. Then filter the crystals produced under suction using a sinter glass filter. Wash with small volumes of ethanol and then ether. Dry by continued suction. 

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