Electrolytic cell drive current in opposite directions. The cell with the larger voltage is discharged, making it a galvanic cell, so P is the cathode and N is the anode as described above. But, the cell with the smaller voltage charges, making it an electrolytic cell. In the electrolytic cell, negative ions are driven towards P and positive ions towards N. Thus, the P electrode of the electrolytic cell meets the definition of anode while the electrolytic cell is being charged. Similarly, the N electrode of the electrolytic cell is the cathode while the electrolytic cell is being charged. As already noted,
Fluoride selective electrode where the fluoride transport number is 1. As transference of charge through the crystal is almost exclusively due to fluoride, the electrode is highly specific to fluoride. The only ion which significantly interferes is hydroxide (OH). Generally such "alkaline error" can be avoided by buffering the sample to a pH below 7. The cell diagram of a typical experimental arrangement is: where: Some commercially available reference electrodes have an internal junction which minimizes the liquid junction potential between the sample solution and the electrolyte in the reference electrode (KCl). The internal electrolyte is at fixed composition and the electrode response