Oxidation and Reduction Definitions of oxidation and reduction Oxidation numbers Redox equations

Oxidation - reduction Oxidation is loss of electrons (OIL) Reduction is gain of electrons (RIG) Oxidation is always accompanied by reduction This is called a redox reaction. An electron transfer reaction. The total number of electrons lost equals the total gained.

Oxidation - reduction Oxidizing agents oxidize and are themselves reduced Reducing agents reduce and are themselves oxidized

Follow the electrons

Oxidation numbers Oxidation number is the number of electrons gained or lost by the element in making a compound Metals are typically considered more 'cation-like' and would possess positive oxidation numbers, while nonmetals are considered more 'anion-like' and would possess negative oxidation numbers.

Predicting oxidation numbers Oxidation number of atoms in element is zero in all cases Oxidation number of element in monatomic ion is equal to the charge. Sum of the oxidation numbers in a compound is zero Sum of oxidation numbers in polyatomic ion is equal to the charge F has oxidation number –1 H has oxidn no. +1; except in metal hydrides where it is –1 Oxygen is usually –2. Except: O is –1 in hydrogen peroxide, and other peroxides O is –1/2 in superoxides KO2 In OF2 O is +2

Position of element in periodic table determines oxidation number GROUP 1A is +1 GROUP 2A is +2 GROUP 3A is +3 (some rare exceptions) GROUP 5A are –3 in compounds with metals, H or with NH4+. GROUP 6A below O are –2 in binary compounds with metals, H or NH4+. GROUP 7A elements are –1 in binary compounds with metals, H or NH4+ or with a heavier halogen.

Identifying reagents Those elements that tend to give up electrons (metals) are typically categorized as reducing agents Those that tend to accept electrons (nonmetals) are referred to as oxidizing agents.

Iron can reduce Cu2+ to Cu The iron nail reduces the Cu2+ ions and becomes coated with metallic Cu. At the same time, the intensity of the blue color diminishes due to loss of Cu2+ ions from solution.

More active metals are strongly reducing

Any element can be both an oxidizer and reducer depending on relative positions in the activity series Fe reduced Cu2+, but Cu can reduce Ag+ (lower activity Fe2+ is reduced by Zn

Predicting results of displacement reactions In this reaction the element metal A displaces the ion metal B from its compound This will only occur if A lies above B in the activity series Displacement reaction exercises

Nuggets of redox processes Where there is oxidation there is always reduction Oxidizing agent Reducing agent Is itself reduced Is itself oxidized Gains electrons Loses electrons Causes oxidation Causes reduction

Identify redox by change in oxidation numbers: follow the flow of electrons Reducing agent increases its oxidation number Oxidizing agent decreases its oxidation number