Zinc amalgam electrodes

In an Evans diagram 89> the mixed potential can easily be found and also be verified by measuring the open circuit potential of a zinc-amalgam electrode in a Cu2+-ion solution. Even the complication by the simultaneous presence of another reducible species, e.g., Pbz+ can be graphically demonstrated for different limiting conditions... 

Carbonic Acid.—Carbonic acid deserves mention here because it can be converted electrolytically into formic acid. Royer 6 observed its formation at zinc and zinc-amalgam electrodes in the electrical reduction of carbonic acid dissolved in water, a current of the gas being conducted through the latter during electrolysis. Klobukow 7 was likewise able to prove the presence of formic acid in water which was electrolyzed and through which a current of carbonic-acid gas was passed. 

A zinc amalgam electrode has been employed as reference electrode in dimethyl sulfoxide (DMSO) [205] and ammonia [206]. The saturated zinc amalgam was prepared [207] by electrolytic deposition of zinc into a layer of pure mercury from an aqueous ZnS04 solution. The solution in equilibrium with the Zn(Hg) consisted of a saturated solution of Zn(C104)2, 4DMSO or ZnCF, 6NH3. 

Clark cell. Standard cell for measuring electrical potential with mercury and zinc amalgam electrodes in zinc sulfate solution. 

Payne, D.A. Bard, A.J. The mechanism of the zinc(II)-zinc amalgam electrode reaction in alkaline media as studied by chronocoulometric and voltammetric techniques. J. Electrochem. Soc. 1972, 119, 1665. 

In the former study, at 298.15 K and 1 M NaC104, potentiometric (zinc amalgam electrode) titration data were used to conclude that two mononuclear complexes were formed ... 

Daniell cell A type of primary voltaic cell with a copper positive electrode and a negative electrode of a zinc amalgam. The zinc-amalgam electrode is placed in an electrolyte of dilute sulphuric acid or zinc sulphate solution in a porous pot, which stands in a solution of copper sulphate in which the copper electrode is immersed. While the reaction takes place ions move through the porous pot, but when it is not in use the cell should be dismantled to prevent the diffusion of one electrolyte into the other. The e.m.f. of the cell is 1.08 volts with sulphmic acid and 1.10 volts with zinc sulphate. It was invented in 1836 by the British chemist John Daniell (1790-1845). 

The simplest way to illustrate the influence of the availability of suitable sites on the electrode on an electrode reaction is to add to the solution a known amount of material which adsorbs to a known extent and study the reaction with and without the presence of this known surface active substance. The inhibiting effect of the adsorbed film is shown in Fig. 38. This curve shows the effect of adsorption of cyclohexanol on the reduction of zinc at a zinc amalgam electrode. One clearly sees that when 6 reaches 0 = 0 5, the inhibiting effect of the cyclohexanol is total, i.e. no current is observed. On the other hand, adsorbed species can provide a way for an alternative path for the mechanism of the reaction studied and may, as a result, act as a catalyst rather than as an Inhibitor. The catalytic effect of diphenylamine on the reduction of water is shown in Fig. 39 hydrogen is... 

This figure demonstrates that also under potentiometric conditions (- no external current flow) electrochemical net reactions occur. The EMF of the zinc-amalgam in a given Zn2 -ion solution depends on the current-voltage characteristic of other ions (in this example, Cu2 and Pb2 are interfering ions with respect to the Zn2 equilibrium potential) at the amalgam electrode. EMF drifts are thus explainable. 

Reductant equivalent weights of, 847 Reduction 409 by chromium(II) salts, 409 by hydrogen sulphide, 416 by Jones reductor (zinc amalgam), 410 by liquid amalgams, 412 by silver reductor, 414 by sulphurous acid, 416 by tin(II) chloride, 415 by titanium(II[), 410 by vanadium(II), 410 see also Iron(III), reduction of Reduction potentials 66 Reference electrodes potentials, (T) 554 Relative atomic masses (T) 819 Relative error 134 mean deviation, 134... 

To describe a specific example of electrode-concentration cells, it is possible to consider two zinc amalgams at different concentrations, dipped into a solution containing zinc ions ... 

Mercury, nickel, copper, zinc, lead, iron, brass, and zinc amalgam were tried as electrode material in respect to their reduction behavior in the reduction of azobenzene to benzidine in alcohol-sulphuric—acid solution. It was shown that the furthest utilizable reduction was obtained with mercury the usefulness of the other metals was determined to be in the following order Lead, sheet nickel, nickel-wire gauze, copper, zinc, iron, and brass. 

Boden, D.P. Wylie, R.B. Spera, V.J. The electrode potential of zinc amalgam in alkaline... 

The influence of mercury on the load capability of a zinc powder electrode (0.2 mm) is illustrated in Figure 7. It is obvious, that amalgamated zinc exhibits an initial peak current of... 

Daniell cell A type of primary cell invented by British chemist John Daniell (1790-1845) in 1836. It consists of two electrodes in different electrolytes separated by a porous pot. The positive electrode is copper immersed in copper(II) sulfate solution and the negative zinc-mercury amalgam electrode is in either dilute sulfuric acid or a zinc sulfate solution. The porous pot prevents mixing of the electrolytes, but allows ions to pass. With sulfuric acid the e.m.f. is about 1.08 volts with zinc sulfate it is about 1.10 volts. 

Equilibrium studies of the metal conplex formation of biopolymers, e.g. polypeptides or proteins can be based on the potentio-metric determination of the free (uncomplexed) metal ion activity in solutions of different pH containing the peptide and the metal ion in different concentrations(16,17). For the measurement of the uncomplexed metal ion concentration in the presence of the metal coordinated by the bioligand, metal electrodes (e.g., silver or mercury), amalgam electrodes (e.g., zinc, cadmium, bismuth), and ion-selective membrane or ion exchange electrodes (e.g., calcium) can be used. The coordination of metal ions to donor atoms protonated at the pH of the solutions to be investigated can be followed by the pH metric equilibrium study of the deprotonation equilibria caused by this process. 

Despite its electrode potential (p. 98), very pure zinc has little or no reaction with dilute acids. If impurities are present, local electrochemical cells are set up (cf the rusting of iron. p. 398) and the zinc reacts readily evolving hydrogen. Amalgamation of zinc with mercury reduces the reactivity by giving uniformity to the surface. Very pure zinc reacts readily with dilute acids if previously coated with copper by adding copper(II) sulphate ... 

Another important primary battery is the mercury cell. It usually comes in very small sizes and is used in hearing aids, watches, cameras, and some calculators. The anode of this cell is a zinc-mercury amalgam the reacting species is zinc. The cathode is a plate made up of mercury(II) oxide, HgO. The electrolyte is a paste containing HgO and sodium or potassium hydroxide. The electrode reactions are... 

The silver reductor has a relatively low reduction potential (the Ag/AgCl electrode potential in 1M hydrochloric acid is 0.2245 volt), and consequently it is not able to effect many of the reductions which can be made with amalgamated zinc. The silver reductor is preferably used with hydrochloric acid solutions, and this is frequently an advantage. The various reductions which can be effected with the silver and the amalgamated zinc reductors are summarised in Table 10.11. ... 

Despite the good agreement, there are two reasons why this test was flawed. First, the anodic half-reaction (5) had of necessity to be carried out at a higher pH, and thus in a different medium from the overall reaction (7). Second, and even more important, the electrode surface in the cathodic half-reaction (6) was not the same as the amalgam surface in reaction (7). Hydrogen evolution could be affected by the presence of zinc sites on the... 

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