Transcript Electrochemistry - Salisbury Composite High School

Electrochemistry
Chemistry 30
Unit 2
• the transfer of electrons in chemical reactions.
Reduction
• operational definition: extraction of metals from
the ore
• theoretical definition: gain of electrons
Reducing agent –species that causes reduction,
and is an electron donor (it is oxidized)
Oxidation
• operational definition : reaction with oxygen
• theoretical definition: loss of electrons
Oxidizing agent – is a species that causes
oxidation by accepting electrons (it is reduced)
• Memory Tips:
• LEO (the lion) says GER (lose electrons and you
are oxidized, gain electrons and you are reduced)
• OIL RIG (oxidation is losing electrons, reduction
is gaining electrons)
Oxidation States
• A method of keeping track of the electrons that are
transferred in a chemical reaction uses the
oxidation states of an atom in an entity.
▫ The apparent net electric charge that an atom would
have if the electron pairs in a covalent bond belonged
entirely to the more electronegative atom.
▫ These are imaginary – they do not represent the
actual charge on the atom
• The oxidation number is the positive or
negative number corresponding to the oxidation
state.
Common Oxidation Numbers
Oxidation
Number
Exceptions
elements
0
Monatomic
ions
Ion charge
hydrogen
+1
-1 in metal
hydrides
oxygen
-2
-1 in
peroxides
(H2O2,
K2O2,
MgO2)
Rules for Assigning Oxidation
Numbers
1.
Assign common oxidation number
2. The oxidation numbers of compounds must add to
zero
2. Molecular compounds: oxidation # assigned to
more electro negative is its regular ion charge
3. Polyatomic Ions: sum of the oxidation numbers
must equal the charge of the ion