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Home :Glossary

Glossary: Redox reactions

A gel made from seaweed used to make salt bridges*.

anode. Compare with cathode*.
The electrode at which oxidation* occurs in a cell. Anions* migrate to the anode.

To coat a metal with a protective film by electrolysis.

autoxidation. autooxidation; autoxidize; autoxidizing.
Oxidation* caused by exposure to air. Rust is an example of autoxidation. Autoxidation makes ether taken from half-filled bottles very dangerous, because air oxidizes ether to highly explosive organic peroxides.

battery acid.
A solution of approximately 6M sulfuric acid* used in the lead storage battery.

cathode. Compare with anode*.
The electrode at which reduction* occurs.

cation. Compare with anion*.
A cation is a positively charged ion. Metals* typically form cations.

corrosion. corrode.
Corrosion is a reaction that involves action of an oxidizing agent* on a metal. The oxidizing agent is often oxygen dissolved in water. See How Iron Rusts for examples.

coulomb. (C)
The SI* unit of electric charge, equal to the amount of charge delivered by a current of 1 ampere* running for 1 second. One mole of electrons has a charge of about 96487 C.

disproportionation. disproportion; disproportionate; disproportionating.
A reaction involving a substance* that produces two different forms of the substance, one more oxidized and the other more reduced than the original.

dry cell. Leclanché cell.
A electrolytic cell* that uses a moist paste rather than a liquid as an electrolyte*. Flashlight batteries are dry cells with a zinc cup for an anode*, a carbon rod for a cathode*, and a paste made of powdered carbon, NH4Cl, ZnCl2, and MnO2 for an electrolyte.

electrochemical cell. electric cell.
A device that uses a redox reaction* to produce electricity, or a device that uses electricity to drive a redox reaction in the desired direction.

electrolytic cell.
A device that uses electricity from an external source to drive a redox reaction*.

The process of driving a redox reaction* in the reverse direction by passage of an electric current through the reaction mixture.

A blood-red complex of Fe2+ ion with 1,10-phenanthroline, used as a redox indicator*. Ferroin changes from red to pale blue when oxidized.

kilogram. (kg)
The kilogram (kg) is the base unit* of mass in the SI* system of units. The standard kilogram is a 1 kg corrosion resistant platinum/iridium cylinder, carefully preserved in the suburbs of Paris (with a backup copy kept in Gaithersburg, Maryland.) Efforts are underway to replace these artifacts by redefining the kilogram as the mass of a certain number of silicon atoms.

oxidation. oxidize; oxidizing; oxidized. Compare with reduction*.
Oxidation is the loss of one or more electrons by an atom, molecule, or ion. Oxidation is accompanied by an increase in oxidation number on the atoms, molecules, or ions that lose electrons.

oxidizing agent. oxidant; oxidizer. Compare with reducing agent*.
A reactant that removing electrons from other reactants in a chemical reaction. Oxidizing agents cause other substances to be oxidized in chemical reactions while they themselves are reduced. For example, nitrate ion is an oxidizing agent in the following reaction:

Cu(s) + 4 H+(aq) + 2 NO3-(aq) rightarrow Cu2+(aq) + 2 H2O(ell) + 2 NO2(g)

Copper gets oxidized (its oxidation number goes from 0 to +2) while the nitrogen gets reduced (from +5 in nitrate to +4 in nitrogen dioxide).

oxidation number. oxidation state; positive valence.
A convention for representing a charge of an atom embedded within a compound, if the compound were purely ionic. For example, H2O is a covalent compound; if it were ionic, the hydrogens would be H+ (oxidation number +1) and the oxygen would be O2- (oxidation number -2). Oxidation number rises for at least one atom in a compound that is oxidized*; oxidation number becomes smaller if the compound is reduced*.

potential difference. electrical potential difference.
Work that must be done to move an electric charge between specified points. Electric potential differences are measured in volts*.

redox indicator. oxidation-reduction indicator.
An organic molecule that has reduced and oxidized forms with different colors; interconversion of the reduced and oxidized forms of the indicator must be reversible. Ferroin* is an example.

redox reaction. electrochemical reaction; oxidation-reduction reaction; redox.
A reaction that involves transfer of electrons from one substance to another. Redox reactions always involve a change in oxidation number for at least two elements in the reactants.

redox titration. oxidation-reduction titration.
A titration* based on a redox* reaction. For example, iron in water can be determined by converting dissolved iron to Fe2+ and titrating the solution with potassium permanganate (KMnO4), a powerful oxidizing agent*.

reducing agent. reductant. Compare with oxidizing agent*.
A reducing agent is a substance that reduce* another substance by supplying electrons to it. Reducing agents cause other substances to be reduced in chemical reactions while they themselves are oxidized. For example, tin(II) is a reducing agent in the following reaction:

Sn2+(aq) + 2 Fe3+(aq) rightarrow Sn4+(aq) + 2 Fe2+(aq)

reduction. reduce; reduced; reducing. Compare with oxidation*.
Reduction is gain of one or more electrons by an atom, molecule, or ion. Reduction is accompanied by a decrease in oxidation number.

salt bridge.
A tube (often filled with ion-laced agar*) that allows two solutions to be in electrical contact without mixing in an electrochemical cell*.

volt. (V)
The SI* unit of electrical potential. One volt equals one joule* per coulomb*.

voltage. (V)
A measured electric potential, in volts*.

voltaic cell. galvanic cell.
An electrochemical cell* that spontaneously generates electrical energy.

voltaic pile.
An early battery* consisting of disks of dissimilar metals (usually zinc and copper) separated by moist paper or cloth soaked in an electrolyte* solution.

An instrument for measuring voltages* and amperages*.

General Chemistry Online! Redox reactions

Copyright © 1997-2010 by Fred Senese
Comments & questions to fsenese@frostburg.edu
Last Revised 08/17/15.URL: http://antoine.frostburg.edu/chem/senese/101/redox/glossary.shtml