Oxidation, Reduction and Electrochemistry In this chapter you will be exposed to some basic concepts involved in a special type of chemical reaction. Time will not permit an in-depth study of this, but the main concepts will be important to learn.
Dec 31, 2015
Oxidation, Reduction and Electrochemistry
In this chapter you will be exposed to some basic concepts involved in a special type of chemical reaction.
Time will not permit an in-depth study of this, but the main concepts will be important to learn.
Oxidation-Reduction Reactions
Oxidation-Reduction reactions are also termed Redox reactions.
A redox reaction is a chemical reaction which involves the loss and gain of electrons.
Redox Reactions
In a redox reaction one substance is oxidized (loses electrons) and another substance is reduced (gains electrons)
OIL RIG ( oxidation is loss, reduction is gain of electrons)
LEO the lion goes GER (loss of electrons is oxidation, gain of electrons is reduction.
2 Na(s) + Cl2(g) 2 NaCl
Na – loses 1 electron (oxidized)
Cl – gains 1 electron (reduced)
Practice Problem
Identify the substance oxidized and reduced in the following redox equation.
Ag (s) + NO3 (aq) AgNO3
Oxidation Numbers
To analyze an equation as a redox reaction it’s essential to identify the oxidation numbers of the reactants and products.
Changes in oxidation numbers reveal if a substance is oxidized or reduced.
Oxidation Number Rules
When assigning oxidation numbers use the following rules:
1) The oxidation number for any “free” or uncombined element in atomic or molecular form is 0.
2) The oxidation number of a monatomic ion is equal to the charge on the ion.
3) The oxidation number of an atom of fluorine in a compound is always –1 because it is the most electronegative.
Oxidation Numbers
4) An atom of the more electronegative element in a binary compound is assigned the number equal to its ion charge.
5) In compounds, atoms of group I, II, and aluminum have positive oxidation numbers : +1, +2, +3 respectively.
6) Hydrogen is +1 unless combined with a metal atom, then its –1.
7) The oxidation number of oxygen is usually –2. When combined with fluorine it is +2. In peroxides, such as H2O2 oxygen has the oxidation number –1.
Oxidation Numbers
8) The sum of the oxidation numbers of all atoms in a particle must equal to zero in a compound and to its charge for a polyatomic ion.
Oxidation Number Practice
NH4+ :
Al :
BF3 :
KClO3
CO32-
Oxidation Number Practice
NH4+ : H= +1 N= -3
Al : 0
BF3 : F=-1 B: +3
KClO3 K=+1 O= -2 Cl= +5
CO32- O= -2 C=+4
Identifying Redox Reactions
To identify a redox reaction you must analyze the oxidation numbers of reactants and products.
Redox Reaction
Identify oxidized and reduced substance:
1) Cl2 + 2HBr 2HCl + Br2
Assign oxidation numbers to each atom in the equation.
0 +1 -1 +1 -1 0
Consider only the atoms for which there was a change in oxidation number.
Identify oxidized and reduced substance:
1) Cl2 + 2HBr 2HCl + Br2
0 +1 -1 +1 -1 0
An increase in oxidation number indicates an oxidation.
A decrease in oxidation number indicates a reduction.
The oxidation number of Cl decreased (from 0 to -1): Cl was reduced
The oxidation number of Br increased (from -1 to 0): Br was oxidized
Identify oxidized and reduced substance:
2) 2H2 + O2 2H2O0 +1 -20
An increase in oxidation number indicates an oxidation.
A decrease in oxidation number indicates a reduction.
The oxidation number of O decreased (from 0 to -2): O was reduced
The oxidation number of H increased (from 0 to +1): H was oxidized
Classwork
Oxidizing and reducing handout