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Influence of the Shape of Transfer Tube on Determining Ion Transference Number by Hittorf Method

In physical chemistry experiment, straight and U-shaped transfer tubes are often used for determining Cu ion transference number by Hittorf method. When a U-shaped transfer tube is used, the result calculated from the concentration change of cathode chamber solution usually has a significant error. The concentration distributions of CuSO4 solution with height in the straight, U and nshaped transfer tubes after electrolysis were investigated via spectrophotometry, using CuSO4 and Cu hoops as electrolyte and electrodes, respectively. It is found that the shape of transfer tube has a great effect on the concentration of central chamber solution. Because the cathode locates at the bottom of the U-shaped and n-shaped transfer tubes, the concentration of central chamber solution changes a lot after electrolysis due to convection caused by the gravity effect, and the concentration of cathode chamber solution is also affected. It would bring a significant error to the measurement of ion transference number. Contrarily, this effect is ignorable if a straight-shaped transfer tube is used, and thus more accurate result can be obtained.