redox reactions
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Redox Reactions. 13.1a Electron Transfer Theory. 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) - PowerPoint PPT PresentationTRANSCRIPT
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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