INSTRUMENT MAINTENANCE PRACTICAL TASK M2. FILLING REFERENCE ELECTRODE Outline Reference electrodes are used in voltage measurements, to provide an unchanging value against which the variations due to the solution can be measured at the working electrode (where the reaction is occurring). The two most common reference electrodes are the silver/silver chloride and calomel (mercury/mercury chloride). In each case, the species producing the voltage are immersed in a salt solution, which through a porous tip in the electrode completes the electrical circuit. The porosity means that the electrolyte will slowly drain out, and needs to be refilled periodically through openings at the top of the electrode barrel. Depending on the design of the electrode, the solution may be KCl or KNO3, and the concentration is important, so you must first establish which solution is required. Procedure 1. Obtain a reference electrode and find out which electrolyte solution is required. 2. Using a dropping pipette, add the electrolyte slowly* until it reaches the fill line or starts overflowing. If you try adding too quickly, the air inside will not be escape and you will get an airlock. Reporting Requirements Complete the Maintenance Log for this instrument.