Transcript 10.1: Oxidization and Reduction Objectives S1

10.1: Oxidization and
Reduction
Objectives S1
Essential Questions
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What is oxidation? Reduction?
How do you assign oxidation numbers?
What is a half reaction?
How do you write half reactions?
Oxidation and Reduction
Reactions
• Oxidation-Reduction reactions (redox) is when
electrons are being gained and lost during a
chemical reaction
• Originally oxidation was defined as gain of
oxygen while reduction was loss of oxygen
Oxidation and Reduction
Reactions (cont)
• Definitions using oxygen were
limited in scope so following
definition are now used:
• Oxidation is loss of electrons
• Reduction is gain of electrons
• OIL RIG
Oxidation and Reduction
Reactions (cont)
Oxidation Numbers
• Oxidization numbers are how we keep track of
what is happening to electrons
• Similar to charge but not exactly the same
• There are set rules when determining
oxidation numbers
Oxidation # Rules
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Oxidation numbers are written per atom
Oxidation number of neutral element by itself is Zero
For most elements the oxidation # correlates with the
charge of atom
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For metals it will equal the metal’s charge
H is +1 when bonded to nonmetals and -1 when bonded
to metals
Cl, Br, and I are -1 except when bonded to F and O
O is usually -2 unless bonded to F
F is always -1
Oxidation # Rules
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Sum of oxidation # for all atoms in a compound is
equal to 0
Sum of oxidation # equal the charge of the ion.
Figure out what you know and use the sum to find the
rest.
Assigning Oxidation Numbers
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Find the oxidation number for each element
Na
CaO
N3SrCl2
NO3CoO
Cu(NO3)2
K2Cr2O7
Cs2(SO4)3
Half Reactions
• Oxidation never occurs without
reduction, they always occur in pairs
• The total formula can be written in two
parts
• The oxidation half (where the oxidation
number has increased)
• The reduction half (where the oxidation
number has decreased/reduced)
Writing Half Reactions
Cu + 2 AgNO3 → Cu(NO3)2 + 2 Ag
• Step 1: Determine Oxidation numbers for each atom on
each side of the equation
• Step two: determine which two atoms have changed
oxidation #s
• Step three: Write half reactions for those two elements
• Step four: Add electrons to balance charges or oxidation
#
• Recall: Oxidation is losing electrons and reduction is
gaining electrons
Balancing Half-Reactions (cont)
• Write balanced half reactions and identify the
elements reduced and oxidized for the
following:
• TiO2 + 2 Mg → Ti + 2 MgO
• Cl2 + 2 NaBr → 2 NaCl + Br2
• 5 CO + I2O5 → I2 + 5 CO2
Essential Questions
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What is oxidation? Reduction?
How do you assign oxidation numbers?
What is a half reaction?
How do you write half reactions?
10.1 Tracked Assignment
• worksheet