Water, electrolysis ionic product

Further examples of recent attempts to reduce the consumption of electrical energy are the electrolysis of aqueous solutions of methanol (but CO2 is still produced at the anode) [78, 79] and water electrolysis using ionic liquids as electrolytes [80]. In the latter case, the authors claimed the possibility of obtaining high hydrogen production efficiencies using an inexpensive material such as low-carbon steel. 

Souza, R. F., PadiUia, J. C., Goncalves, R. S., Souza, M. O., Berthelot, J. R. (2007). Electrochemical hydrogen production from water electrolysis using ionic liquid as electrolytes towards the best device. Journal of Power Sources, 164, 792—798. 

In an electrolytic cell, an external energy source makes a nonspontaneous redox reaction (AG > 0) occur. In electrolysis of a molten binary ionic compound (salt), the cation is reduced to the metal and the anion is oxidized to the nonmetal. For an aqueous salt solution, the products depend on whether water or one of the ions of the salt requires less energy to be reduced or oxidized. 

For kaolinite clay at 50 10% water saturation, Acar et al. [8,36] and Putnam (91 have reported that the measured coefficient of water transport efficiency, ki, decreased from a maximum of about 1.8 L/A-hr at 15 hours of processing to 0.2 L/A-hr at 150 hours, for an electrode current density 0.05 mA/cm2. in many tests, a short induction period with no flow occurred after switching on the current (this has even been observed in single capillary experiments [18, Fig. 4]). The flow then quickly increased to a maximum value. Similar behaviour was found in some tests with low levels of contaminant present, e.g., for decontamination of 130 ppm Pb2+ ion from kaolinite at a current density 0.04 mA/cm, Hamed et al. [37,38] report a decrease in ki from a maximum of 2.7 L/A-hr. to approx. 0.4 L/A-hr. at 600 hours. Figure 5. These initial ki values are consistent with those found in earlier studies [6] but measured efficiencies will vary with the clay type and preparation, such as the degree of prewashing, the residual ionic salt content, water saturation, etc. The marked decrease in the water transport with time probably is caused mainly by the accumulation and reaction of ionic electrolysis products. 

Because of the high melting points of ionic substances, the electrolysis of molten salts requires very high temperatures. Do we obtain the same products if we electrolyze the aqueous solution of a salt instead of the molten salt Frequently the answer is no because water itself might be oxidized to form O2 or reduced to form H2 rather than the ions of the salt. 

The fluoride ISE is used routinely for measuring fluoridated water and fluoride ion in dental products such as mouthwash. A 50 mL aliquot of water containing sodium fluoride is analyzed using a fluoride ion electrode and the MSAs. The pH and ionic strength are adjusted so that all fluoride ion is present as free F" ion. The potential of the ISE/reference electrode combination in a 50 mL aliquot of the water was -0.1805 V. Addition of 0.5 mL of a 100 mg/L F ion standard solution to the beaker changed the potential to -0.3490 V. Calculate the concentration of (1) fluoride ion and (2) sodium fluoride in the water sample. Copper is deposited as the element on a weighed Pt cathode from a solution of copper sulfate in an electrolytic cell. If a constant current of 0.600 A is used, how much Cu can be deposited in 10.0 min (Assume no other reductions occur and that the reaction at the anode is the electrolysis of water to produce oxygen.)... 

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