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A: Symbol
and abbreviation of ampere.
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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.
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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.
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Accumulator:
See rechargeable battery.
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Acid: A compound
that dissociates to produce hydrogen (H+) cations when dissolved in water. See
also pH.
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Acidity:
See pH.
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Activation overpotential
(overvoltage):
Contribution to the total overpotential due to the charge transfer step at the
electrode interface.
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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.
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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.
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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.
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Activation overpotential
(polarization): The overpotential (alternatively called polarization)
associated with the charge-transfer reaction elementary step in the overall
electrode reaction.
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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.
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Activity coefficient:
See activity.
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Adsorbate:
A material that is adsorbed.
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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.
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Ah: Symbol
and abbreviation of ampere-hour.
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Alkali: See
base.
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Alkalinity:
See pH.
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Alkali production:
See brine electrolysis.
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Alkaline battery:
See Edison battery.
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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.
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Alternating current:
See current. Abbreviated as "ac."
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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.
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Amalgam:
An alloy of mercury and another metal.
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Ammeter:
Instrument used for the measurement of current.
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Amp: Symbol
and abbreviation of ampere.
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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".
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Ampere-hour efficiency:
See coulometric efficiency.
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Amperometry:
An electroanalytical technique based upon the measurement of the current flowing
through the working electrode of an electrochemical cell.
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Amperostat:
See galvanostat.
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Analyte:
A substance whose chemical composition is to be determined by chemical analysis.
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Anhydrous:
A substance that does not contain water. The opposite of hydrous.
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Anion: A
negatively charged ion.
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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.
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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.
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Anode mud:
The insoluble residue that derives from the anodic dissolution of an
impure metal such as copper during electrorefining. Also called "anode slime."
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Anode slime:
See anode mud.
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Anodic partial current
(density): See partial current density.
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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.
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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.
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Anolyte:
The electrolyte on the anode side of an electrochemical cell that is divided
into compartments.
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Aqueous solution:
A solution with water as the solvent.
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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.
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Atomic weight:
The average relative weight of a chemical element as it occurs in nature
referred to some element taken as a standard.
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Auxiliary electrode:
See counter electrode.
