Polarography is a method of chemical analysis, particularly for metals or organic groups, that can measure tiny concentrations of ions in solution. Two electrodes are inserted in the solution: one, the reference electrode, is kept at a constant voltage, the other has a variable voltage and consists of a glass capillary tube containing a head of mercury, with tiny drops of mercury on its end becoming the face of the electrode. As these drops form, a current grows to a peak between the two electrodes and then suddenly falls as the drop leaves the capillary tip. By gradually increasing the voltage, a polarogram – a graph of the current versus the voltage, which looks like a series of steps – is produced. From these, the reduction potentials of the ions in the solution may be deduced and, as these are known for each metal ion, the ions can be identified.
Related category• ANALYTICAL CHEMISTRY
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