Redox Reactions
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Transcript of Redox Reactions
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Redox Reactions
13.1a Electron Transfer Theory
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Overview
• oxidation and reduction rxtns always occur together (redox rxtn)– you can’t have one without the other
• examples– extracting metal from an ore– electroplating of metals– salt on roads (corrosion)
• salt accelerates the reaction between oxygen and metal• makes electron transfer easier
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3 perspectives of oxidation/reduction
• 1) oxygen– oxidation gains and reduction loses
• 2) hydrogen– oxidation loses and reduction gains
• 3) electrons (modern view)– oxidation loses and reduction gains– most fundamental explanation, what we will
be working with the most
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Sample Rxtn.
We convert iron ore to metallic iron using carbon. What is being oxidized?
2Fe2O3 + 3C 4Fe + 3CO2
– we removed oxygen from the iron(III)oxide and the carbon gained oxygen
– carbon was oxidized because it gained an oxygen
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Sample Rxtns. con’t
Fe2O3 (s) + 3 CO(g) 2 Fe (s) + 3CO2
(g)
SnO2 (s) + C(s) Sn(s) + CO2 (g)
CuS(s) + H2(g) Cu(s) + H2S(g)
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Oxidation Reduction
Gains oxygen Lose Oxygen
Lose Hydrogen Gains hydrogen
Lose Electrons Gains electrons
Oxygen
Hydrogen
e-
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Redox with ElectronsRedox with Electrons
many reactions may not even involve oxygen redox currently refers to electrons being
transferred between reactants
Mg + S Mg2+ + S2-
•the magnesium atom (which has zero charge) changes to a magnesium ion by losing 2 electrons, and is oxidized to Mg2+
•the sulfur atom (which has no charge) is changed to a sulfide ion by gaining 2 electrons, and is reduced to S2-
•Mg is the reducing agent and S is the oxidizing agent
• agents cause the other half of the rxtn. to occur
(MgS)
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Examples
• Is the reactant oxidized or reduced?
• Pb PbO3 oxidized • SnO2 SnO reduced• KClO3 KCl reduced• C2H6O C2H4O oxidized• C2H2 C2H6 reduced
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Homework
Textbook p. 559 #1-4
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Redox Reactions
13.1a1 Electron Transfer Theory
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Leo the Lion!
• LEO the lion says GER– Loss of electrons is oxidation, gain of
electrons is reduction
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LEO says GERLEO says GER
0 1
Na Na e
Lose Electrons = Oxidation
Sodium is oxidized
Gain Electrons = Reduction
0 1
Cl e Cl
Chlorine is reduced
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LEO says GER con’tLEO says GER con’t - losing electrons is oxidation, and the substance that loses the electrons is called the reducing agent. - gaining electrons is reduction, and the substance that gains the electrons is called the oxidizing agent.
Mg(s) + S(s) MgS(s)
Mg is oxidized: loses e-, becomes a Mg2+ ion
S is reduced: gains e- = S2- ion
Mg is the reducing
agent
S is the oxidizing agent
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Oxidizing and Reducing Agents
CuO + H2 Cu + H2O
• Cu goes from 2+ to 0– Cu is reduced, therefore it is called an
oxidizing agent because it causes some other substance to be oxidized
• H goes from 0 to 1+– H is oxidized, therefore it is called a reducing
agent because it causes some other substance to be reduced
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Identifying Agents in an Equation
• CuO + H2 Cu + H2O
Reduction: CuO is the oxidizing agent
Oxidation: H2 is the reducing agent
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• A) H2(g) + Cl2 (g) 2HCl(g)• H2 oxidized Cl2 reduced
• B) S(s) + Cl2 (g) SCl2(g)• S oxidized Cl2 reduced
• C) N2 + 2O2 2NO2
• N2 oxidized O2 reduced
• D) 2Li + F2 2LiF• Li oxidized F2 reduced
• E) H2 + S H2S• H2 oxidized S reduced
Examples
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Half-Cell Reactions
The overall reaction:
2Fe + 3Cl2 2Fe3+ + 6Cl-
may be written as the sum of two half-cell reactions:
2Fe 2Fe3+ + 6e- (oxidation)
3Cl2 + 6e- 6Cl- (reduction)
Complete redox reactions can be expressed as the sum of two half reactions, one reduction and one oxidation.
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Homework
Textbook p.564 #7-11
LSM 13.1B,C summary