For water content determination why we don’t use single platinum electrode? What is tge use of double platinum electrode?
At the beginning and during the titration as long as the iodine generated reacts with the water, there is no free iodine in the titration solution. A voltage of ca. 400 mV to 650 mV is necessary to maintain the set polarization current at the double pin electrode.
At the end of the titration when all the water in the sample has reacted with the iodine, free iodine is present in the titration solution. This free iodine gives rise to “ionic conduction”. Now a low voltage of 50 mV to 100 mV is required to keep the polarization current constant. This drop in voltage is used to indicate the end of the titration. Ionic conduction means Iodine takes up an electron at the negatively charged platinum pin of the indicator electrode and is thereby reduced to iodide (I-). Iodide ions, which are present in excess in the titration solution, then releases the electron again at the positively charged platinum pin and is again oxidized to iodine. Therefore to determine end point with Ionic conduction we need Two Pins and single pin will not be sufficient