37l Coulometric Titrations

Notes 1. Alternatively, grease and organic materials can be removed by heating platinum electrodes to redness in a flame. Do not touch electrode surfaces with your fingers after cleaning because grease and oil cause nonadherent deposits that can flake off during washing and weighing. 2. Chloride ion must be totally excluded from this determination because it attacks the platinum anode during electrolysis. This reaction not only is destructive but also causes positive errors in the analysis by codepositing platinum with copper on the cathode. 3. If desired, the tin content can be determined gravimetrically by ignition of the SnO2 xH2O to SnO2. 4. It is important to maintain a potential between the electrodes until they have been removed from the solution and washed. Some copper may redissolve if this precaution is not observed. 5. Experience has shown that a small amount of moisture is retained by the PbO2 and that better results are obtained if 0.8643 is used instead of 0.8662, the stoichiometric factor.