(Solution) - Chemical oxygen demand by coulometry An electrochemical device incorporating photooxidation -(2025 Original AI-Free Solution)
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Chemical oxygen demand by coulometry. An electrochemical device incorporating photooxidation on a TiO2 surface could replace refluxing with Cr2O72- to measure chemical oxygen demand (Box 15-2). The diagram below shows a working electrode held at + 0.30 V versus Ag | AgCl and coated with nanoparticles of TiO2. Upon ultraviolet irradiation, electrons and holes are generated in the TiO2. Holes oxidize organic matter at the surface. Electrons reduce H2O at the auxiliary electrode in a compartment connected to the working compartment by a salt bridge. The sample compartment is only 0.18 mm thick with a volume of 13.5 ?L. It requires 1 min for all organic matter to diffuse to the TiO2 surface and be exhaustively oxidized.
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CcHhOoNnXx + AH2O ? BCO2 + CX- + DNH3 + EH+ + Fe-
where X is any halogen. Express the stoichiometry coefficients A, B, C, D, E, and F in terms of c, h, o, n, and x.
(b) How many molecules of O2 are required to balance the halfreaction in part (a) by reduction of oxygen (O2 + 4H- + 4e- ? 2H2O)?
(c) The area between the two curves in the graph is ??0(Isample - Iblank) dt = 9.43mC. this is the number of electrons O2 would be required for the same oxidation?
(d) Chemical oxygen demand (COD) is expressed as mg of O2 required to oxidize 1 L of sample. Find the COD for this sample.
(e) If the only oxidizable substance in the sample were C9H6NO2ClBr2, what is its concentration in mol/L?