| 释义 |
DictionarySeeelectrodeSee Hydrogen Electrode
Hydrogen Electrode
hydrogen electrode[′hī·drə·jən i′lek‚trōd] (physical chemistry) A noble metal (such as platinum) of large surface area covered with hydrogen gas in a solution of hydrogen ion saturated with hydrogen gas; metal is used in a foil form and is welded to a wire sealed in the bottom of a hollow glass tube, which is partially filled with mercury; used as a standard electrode with a potential of zero to measure hydrogen ion activity. Hydrogen Electrode a platinum plate coated with an electrodeposit of platinum black that is immersed in an acid solution having a specific concentration of hydrogen ions H+ and bathed in a flow of gaseous hydrogen. The potential of the hydrogen electrode is produced by the reversible reaction  . An equilibrium is established between the hydrogen adsorbed by the platinum black and the hydrogen ions in the solution. The potential on the electrode E is determined from the Nernst equation 
where T is the absolute temperature (°K), aH+ is the active concentration of hydrogen ions (g-ion/l), p is the hydrogen pressure [kgf/cm2 (atm)], and E° is the normal (or standard) potential of the hydrogen electrode when p = 1 kgf/cm2 (1 atm) and aH+ = 1. For any given temperature, E° is conventionally considered to be zero. The potentials of all other electrodes are calculated with respect to the hydrogen electrode (the so-called hydrogen potential scale). When working with a hydrogen electrode, the hydrogen must be carefully purified from admixtures. Sulfur and arsenic compounds are especially hazardous as is oxygen, which reacts with the hydrogen on the surface of the platinum to form water that disturbs the equilibrium  . This electrode is employed as a reference electrode. hydrogen electrode
electrode [e-lek´trōd] either of two terminals of an electrically conducting system or cell; specifically, the uninsulated portion of a lead that is in direct contact with the body.active electrode therapeutic electrode.calomel electrode one capable of both collecting and giving up chloride ions in neutral or acidic aqueous media, consisting of mercury in contact with mercurous chloride; used as a reference electrode in pH measurements.depolarizing electrode an electrode that has a resistance greater than that of the portion of the body enclosed in the circuit.hydrogen electrode an electrode made by depositing platinum black on platinum and then allowing it to absorb hydrogen gas to saturation; used in determination of hydrogen ion concentration.indifferent electrode one larger than a therapeutic electrode, dispersing electrical stimulation over a larger area.point electrode an electrode having on one end a metallic point; used in applying current.therapeutic electrode one smaller than an indifferent electrode, producing electrical stimulation in a concentrated area; called also active electrode.hy·dro·gen e·lec·trodethe ultimate standard of reference in all pH determinations, limited and technically difficult to use, consisting of a piece of spongy platinum black partly immersed in a solution in a small glass tube; the tube above the solution is filled with hydrogen gas that is bubbled through the solution and absorbed by the platinum; the electrode thus measures the potential between H2 and H+, the "standard" potential of which (1 atmosphere, 1 molar) is taken as zero; hence, the hydrogen electrode potential measures [H+] or pH.hydrogen electrodeAn electrode that absorbs and measures hydrogen gas; used as the reference for pH measurement in research laboratories. See also: electrode |