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Electrochemistry Dictionary - A

  • A: Symbol and abbreviation of ampere.

  • Absorption: A process "to take in and incorporate." E.g., light can be "absorbed" by a material. In chemistry, a term often used to describe the dissolution of a gas into a liquid or solid. The dissolving gas is said to be "absorbed." Or a liquid substance can be "absorbed" by a solid. This is a bulk process, not to be confused with adsorption.

  • AC: Abbreviation of alternating current. However this term is also used in connection with ac voltage, that is, an "alternating" voltage that will cause an "ac current" to flow in a conductor, and also in connection with ac power.

  • Accumulator: See rechargeable battery.

  • Acid: A compound that dissociates to produce hydrogen (H+) cations when dissolved in water. See also pH.

  • Acidity: See pH.

  • Activation overpotential (overvoltage): Contribution to the total overpotential due to the charge transfer step at the electrode interface.

  • Active mass or material: The material in an electrochemical cell which takes part in the cell reaction. For example, the lead contained in the positive plate of a lead-acid battery.

  • Active material utilization: The fraction of active material that reacts during discharge before the battery can no longer deliver the required current at a useful voltage.

  • Active metal: A metal that is easily oxidized (corroded) in air. For example, sodium will violently react with air, aluminum will always have an air-formed oxide film on its surface, and iron is easily rusted. These metals have high negative standard electrode potentials and are high the on the electromotive series. Contrast with noble metal.

  • Activation overpotential (polarization): The overpotential (alternatively called polarization) associated with the charge-transfer reaction elementary step in the overall electrode reaction.

  • Activity : The activity of a dissolved species in solution is the "effective" concentration of that species. In an "ideal" solution, the molecules in the solution do not interact with each other and the concentration and the activity are identical. This is the case for very dilute solutions. In a "real" solution, there is a certain interaction between the molecules resulting in a diminished "activity" of the molecules toward the outside world, and the solution behaves like it would contain lower concentration of the dissolved species than it actually does. The activity can be expressed as the product of an "activity coefficient" and the concentration.

  • Activity coefficient: See activity.

  • Adsorbate: A material that is adsorbed.

  • Adsorption: An increase of the concentration of a solute in the vicinity of a solid surface, over that in the bulk of the solution, due to the attractive interaction between the solid immersed into the solution and the solute. Adsorption on a solid from a gaseous phase also occurs. It is a surface process, not to be confused with absorption. Opposite: desorption.

  • Ah: Symbol and abbreviation of ampere-hour.

  • Alkali: See base.

  • Alkalinity: See pH.

  • Alkali production: See brine electrolysis.

  • Alkaline battery: See Edison battery.

  • Alkaline cell: A modern version of the Leclanche cell containing basic (potassium hydroxide that is very corrosive) electrolyte. It has considerably improved characteristics and it is slowly replacing the Leclanche cell.

  • Alternating current: See current. Abbreviated as "ac."

  • Aluminum production: Aluminum metal is produced by electrolysis of aluminum oxide dissolved in a high-temperature molten-salt electrolyte. Aluminum is deposited as a liquid metal on the cathode of the electrolytic cell (the aluminum cations are reduced to liquid metal). This is the only large-scale industrial process for the production of aluminum.

  • Amalgam: An alloy of mercury and another metal.

  • Ammeter: Instrument used for the measurement of current.

  • Amp: Symbol and abbreviation of ampere.

  • Ampere: Measurement unit of current. Abbreviation: "A" or "amp".

  • Ampere-hour: An alternative unit of electrical charge. One ampere-hour = 3,600 coulombs. Symbol: "Ah".

  • Ampere-hour efficiency: See coulometric efficiency.

  • Amperometry: An electroanalytical technique based upon the measurement of the current flowing through the working electrode of an electrochemical cell.

  • Amperostat: See galvanostat.

  • Analyte: A substance whose chemical composition is to be determined by chemical analysis.

  • Anhydrous: A substance that does not contain water. The opposite of hydrous.

  • Anion: A negatively charged ion.

  • Anode: The electrode where oxidation occurs in an electrochemical cell. It is the positive electrode in an electrolytic cell, while it is the negative electrode in a galvanic cell. The current on the anode is considered a positive current according to international convention; however, in electroanalytical chemistry the anodic current is often considered negative. Contrast with cathode.

  • Anode effect: A condition in an electrolytic cell that produces an abrupt increase in cell voltage and a decrease in current flow. It is usually caused by the temporary formation of an insulating layer on the anode surface. It occurs almost exclusively in molten salt electrolysis, such as in aluminum production.

  • Anode mud: The insoluble residue that derives from the anodic dissolution of an impure metal such as copper during electrorefining. Also called "anode slime."

  • Anode slime: See anode mud.

  • Anodic partial current (density): See partial current density.

  • Anodic (corrosion) protection: A process for corrosion protection of a metal or alloy achieved by impressing upon the metal an anodic current of sufficient magnitude to cause the formation of a passive film. Anodic protection is effective only for metals that are prone to passivate, such as stainless steel and titanium. See also an Encyclopedia Article and cathodic protection.

  • Anodizing: A process to produce an oxide film or coating on metals and alloys by electrolysis. The metal to be treated is made the anode in an electrolytic cell and its surface is electrochemically oxidized. Anodization can improve certain surface properties, such as corrosion resistance, abrasion resistance, hardness, appearance, etc. One metal very often anodized is aluminum, all the above properties improve, furthermore, since the surface film is porous, the aluminum metal can even be colored by the application of pigments or dies in the pores.

  • Anolyte: The electrolyte on the anode side of an electrochemical cell that is divided into compartments.

  • Aqueous solution: A solution with water as the solvent.

  • Atom, atomic structure (proton, neutron, electron): The smallest physical unit of a chemical element that can still retain all the physical and chemical properties of that element. Atoms combine to form molecules, and they themselves contain several kinds of smaller particles. An atom has a dense central core (the nucleus) consisting of positively charged particles (protons) and uncharged particles (neutrons). Negatively charged particles (electrons) are scattered in a relatively large space around this nucleus and move about it in orbital patterns at extremely high speeds. An atom contains the same number of protons as electrons and thus is electrically neutral (uncharged) and stable under most conditions.

  • Atomic weight: The average relative weight of a chemical element as it occurs in nature referred to some element taken as a standard.

  • Auxiliary electrode: See counter electrode.