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Oxidation and Reduction. Introduction to Oxidation and Reduction. Early attempts to define oxidation and reduction were based on observations of the gain and loss of oxygen and hydrogen during a chemical change.
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Introduction to Oxidation and Reduction • Early attempts to define oxidation and reduction were based on observations of the gain and loss of oxygen and hydrogen during a chemical change. • These definitions are still useful in some cases, particularly in organic chemistry, but they have largely been replaced by a more inclusive approach.
Oxidation and Reduction • Oxidation and Reduction are now defined as the transfer of electrons . • Oxidation is the loss of electrons and Reduction is the gain of electrons (OILRIG) • Oxidation and reduction will always occur together. • Reactions of this type are called REDOX reactions
Oxidation States • Oxidation states can be used to track oxidation change. • Oxidation state is the value assigned to each atom in a compound and it is a measure of the electron control or possession it has relative to the atom in the pure element. • Oxidation state enables us to keep track of the relative electron density in a compound and how it changes during a reaction. • There are two parts to the oxidation state:
Interpreting Oxidation States • The element sulfur can have a wide range of oxidation states in different compounds. • The more positive the oxidation state is, the more the atom has lost control over the electrons, so the more oxidized it is. • The more negative the oxidation state is, the more the atom has gained control over electrons, so the more reduced it is. • Therefore, H2S represents sulfur in its most reduced form and SO3 and H2SO4 represent sulfur in its most oxidized form. • So, by keeping track of the oxidation states, one can determine which species was reduced and which was oxidized; an increase in oxidation state means oxidation and a decrease in oxidation number means reduction.
Writing Half-Equations • A redox reaction can be separated into the two processes – oxidation and reduction. • These are called half-equations. • Electrons are added on one side of each equation to balance the charges.
