Potassium standard reduction potentials

CBL System voltage probe filter paper (6 pieces size 0.6 cm by 2.5 cm) 1M potassium nitrate forceps steel wool or sandpaper table of standard reduction potentials... 

Biofuel Cell At the cathode of a biofuel cell, Fe " " in potassium hexacyanoiron(III) (K3[Fe(CN)6]) is reduced to Fe + in potassium hexacyanoiron(II) (K4[Fe(CN)6]). At the anode, reduced nicotinamide-adenine-dinucleotide (NADH) is oxidized to NAD+. Use the following standard reduction potential to determine the potential of the cell. 

In order to measure the emf of a given half-cell, it is necessary to connect it with a second half-cell and measure the voltage produced by the complete cell. In general, the second halfcell serves as a reference cell and should be one with a known, stable electrode potential. Although the standard hydrogen electrode serves to define the standard reduction potential, in practice it is not always convenient to use an SHE as a reference electrode. It is difficult to set up and control. Other, more convenient reference electrodes have been developed. In principle, any metal-ion half-cell could be used under controlled conditions as a reference electrode, but in practice, many metals are unsatisfactory materials. Active metals, such as sodium and potassium, are subject to chemical attack by the electrolyte. Other metals, such as iron, are difficult to obtain in the pure form. With some metals, the ionic forms are unstable to heat or to exposure to the air. Also, it is frequently difficult to control the concentration of the electrolytes accurately. As a result, only a few systems provide satisfactory stable potentials. 

Explain in your own words why (a) the standard reduction potentials of potassium, rubidium, and cesium are so similar and />) why the standard reduction potential of lithium is so different from the above three. 

Table A. 13 in the appendix gives values for standard reduction potentials for a number of half-cells. Longer versions of such tables are available in handbooks. Unfortunately, some older works use values that are the negative of the standard reduction potentials (they are called oxidation potentials). If you are not certain whether an old table gives reduction potentials or oxidation potentials, look for an active metal electrode such as sodium or potassium. If the table contains reduction potentials, the half-cell potential of such a metal electrode will be negative.

Chloride ions will be discharged at a platinum, graphite or magnetite anode from saturated neutral solutions of sodium or potassium chloride rather than hydroxyl ions although at equilibrium conditions it should be the very opposite, as the reversible deposition potential (reduction potential) of oxygen in neutral solution is much lower ) (7Eoh- i o2. Pt = 0.815 V at 25 °C) than the standard... 

BrOj" and reductants such as FeJ+, AsOj", Ti34 and S20 ". The titration curves are often unsymmetrical due to the stoichiometry of the reaction, but the error is small (<1 %) or can be eliminated by titrating standards. If the reduction potentials of two species differ by >0.2 V, separate inflections will be observed when titrating the mixture, e.g. the titration of Fe2 and Ti3 with potassium permanganate. 

Partition coefficients in the octanol-pH 7.4-phosphate-buffer system. c Nitrothiazole oxidation-reduction potentials (volts) as calculated from their half-wave potentials, as determined using a Polarecord E 261 polarograph (Metrohm AG, Herisau, Switzerland) and a saturated Ag/AgCl reference electrode. Measurements were performed at 20°C and a drop time of 1 drop/2.8 sec. The compounds were dissolved in 1 ml dimethyl formamide and added to 24 ml of a borax-potassium biphosphate buffer of pH 7.3 [prepared according to J. M. Kolthoff, J. Biol. Chem. (1925) 68, 135]. A pH of 7.4 resulted. Standard error of determination 3 mv. 

An aqueous solution of potassium permanganate (KMn04) appears deep purple. In aqueous acidic solution, the permanganate ion can be reduced to the pale-pink manganese(II) ion (Mn ). Under standard conditions, the reduction potential of an MnOijlMn half-cell is = 1.49 V. Suppose this half-cell is combined with a Zn Zn half-cell in a galvanic cell, with [Zn ] = [MnO ] = [Mn ] = [H3O ] = 1 M. (a) Write equations for the reactions at the anode and the cathode, (b) Write a balanced equation for the overall cell reaction, (c) Calculate the standard cell potential difference, A%°. 

Voltammetric experiments were carried out with solutions containing different organic acids and an excess of supporting electrolyte (sodium or potassium sulfate). The presence of the latter substance made it possible to minimize the effect of migration on the mass transport processes. The acids under study are listed in Table 11.1 their symbols LH or LH2 render a number of mobile protons (H" ions) that can be released in acidic water solutions. Due to a sufficiently high difference between the standard potentials ofCu Cu " andH2 H electrodes, partial processes of Cu(II) reduction and hydrogen evolution are well-separated. 

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