•Redox ChemistryOxidation and ReductionElectrochemistry

Syllabus Statements, First Exams 20099.1.1 Define oxidation and reduction in terms of electron

loss and gain. 9.1.2 Deduce the oxidation number of an element in a

compound. 9.1.3 State the names of compounds using oxidation

numbers. 9.1.4 Deduce whether an element undergoes oxidation or

reduction in reactions using oxidation numbers.9.2.1 Deduce simple oxidation and reduction half-equations

given the species involved in a redox reaction. 9.2.2 Deduce redox equations using half equations.9.2.3 Define the terms oxidizing agent and reducing agent.

ReactionsPrecipitation: cations and anions come together to

form insoluble ionic compounds.

Equation2 KI (aq) + Pb(NO3)2 (aq) PbI2 (s) + 2 KNO3 (aq)

Complete Ionic Equation2 K+ (aq) + 2 I- (aq) + Pb2+ (aq) + 2 NO3

- (aq) PbI2 (s) + 2 K+ (aq) + 2 NO3- (aq)

Net Ionic Equation 2 I- (aq) + Pb2+ (aq) + PbI2 (s)

Did the charge on any of the species in this reaction change?e.g. What charge did K start with? Finish with?What charge did Pb start with? Finish with?

ReactionsSingle-replacement reactions: One metallic element

replaces another metallic element in a salt.Equation

3 CuCl2 (aq) + 2 Al (s) 2 AlCl3 (aq) + 3 Cu (s)

Complete Ionic Equation 3 Cu2+ (aq) + 6 Cl- (aq) + 2 Al (s) 2 Al3+

(aq) + 6 Cl- (aq) + 3 Cu (s)

Net Ionic Equation3 Cu2+ (aq) + 2 Al (s) 2 Al3+ + 3 Cu (s)

Did the charge on any of the species in this reaction change?

YES!

Electrochemical Reactions

In electrochemical reactions, electrons are transferred from one species to another.

Translation: Redox reactions involve the gaining and losing of electrons.

Oxidation Numbers

In order to keep track of what loses electrons and what gains them, we assign oxidation numbers.

Assigning Oxidation Numbers

Use the chart given and identify the oxidation state of nitrogen in each of the compounds/ions given.

Examples…

NH3 N2H4 N2 N2O NO NO2 NO3-

-3 -2 0 +1 +2 +4 +5

How’d you do?Any questions?

Oxidation

• A species is oxidized when it loses electrons.• Here, zinc loses two electrons to go from neutral

zinc metal to the Zn2+ ion.

Oxidation and Reduction

• A species is reduced when it gains electrons.• Here, each of the H+ gains an electron and they

combine to form H2.

LEO the lion goes GER

Loss of Electrons is Oxidation

Gain of Electrons is Reduction

Mnemonic Device

OIL RIG

Oxidation Is Loss (of electrons)Reduction Is Gain (of electrons)

King Phillip Came Over For Great SupperKingdomPhylumClassOrderFamilyGenusSpecies

Oxidation and Reduction

• What is reduced is the oxidizing agent.– H+ oxidizes Zn by taking electrons from the zinc, being reduced

in the process.• What is oxidized is the reducing agent.

– Zn reduces H+ by giving it electrons, being oxidized in the process.

Example ReactionIdentify the following:

Element oxidizedElement reducedOxidizing agentReducing agent

2 PbS (s) + 3 O2 (g) 2 PbO (s) + 2 SO2 (g)

Example ReactionIdentify the following:

Element oxidized SulfurElement reducedOxidizing agentReducing agent

2 PbS (s) + 3 O2 (g) 2 PbO (s) + 2 SO2 (g)

Example ReactionIdentify the following:

Element oxidized SulfurElement reduced OxygenOxidizing agentReducing agent

2 PbS (s) + 3 O2 (g) 2 PbO (s) + 2 SO2 (g)

Example ReactionIdentify the following:

Element oxidized SulfurElement reduced OxygenOxidizing agent O2 (g)Reducing agent

2 PbS (s) + 3 O2 (g) 2 PbO (s) + 2 SO2 (g)

Example ReactionIdentify the following:

Element oxidized SulfurElement reduced OxygenOxidizing agent O2 (g)Reducing agent PbS (s)

2 PbS (s) + 3 O2 (g) 2 PbO (s) + 2 SO2 (g)

Example ReactionIdentify the following:

Element oxidizedElement reducedOxidizing agentReducing agent

Mg (s) + CuSO4 (aq) MgSO4 (aq) + Cu (s)

Example ReactionIdentify the following:

Element oxidized MagnesiumElement reducedOxidizing agentReducing agent

Mg (s) + CuSO4 (aq) MgSO4 (aq) + Cu (s)

Example ReactionIdentify the following:

Element oxidized MagnesiumElement reduced CopperOxidizing agentReducing agent

Mg (s) + CuSO4 (aq) MgSO4 (aq) + Cu (s)

Example ReactionIdentify the following:

Element oxidized MagnesiumElement reduced CopperOxidizing agent CuSO4 (aq)Reducing agent

Mg (s) + CuSO4 (aq) MgSO4 (aq) + Cu (s)

Example ReactionIdentify the following:

Element oxidized MagnesiumElement reduced CopperOxidizing agent CuSO4 (aq)Reducing agent Mg (s)

Mg (s) + CuSO4 (aq) MgSO4 (aq) + Cu (s)

Another Example Reaction

5Fe2+(aq) +MnO4- (aq) +8H+(aq) → 5Fe3+(aq) + Mn2+(aq) + 4H2O(l)

Identify the following:Element oxidizedElement reducedOxidizing agentReducing agent

Another Example Reaction

5Fe2+(aq) +MnO4- (aq) +8H+(aq) → 5Fe3+(aq) + Mn2+(aq) + 4H2O(l)

Identify the following:Element oxidized Fe2+

Element reducedOxidizing agentReducing agent

Another Example Reaction

5Fe2+(aq) +MnO4- (aq) +8H+(aq) → 5Fe3+(aq) + Mn2+(aq) + 4H2O(l)

Identify the following:Element oxidized Fe2+

Element reduced MnOxidizing agentReducing agent

Another Example Reaction

5Fe2+(aq) +MnO4- (aq) +8H+(aq) → 5Fe3+(aq) + Mn2+(aq) + 4H2O(l)

Identify the following:Element oxidized Fe2+

Element reduced MnOxidizing agent MnO4

- (aq)Reducing agent

Another Example Reaction

5Fe2+(aq) +MnO4- (aq) +8H+(aq) → 5Fe3+(aq) + Mn2+(aq) + 4H2O(l)

Identify the following:Element oxidized Fe2+

Element reduced MnOxidizing agent MnO4

-

Reducing agent Fe2+

Reactivity Series

Some metals make better reducing agents than other metals. (In other words, some metals are oxidized easier.)

Let’s look at two reactions:

Mg (s) + CuCl2 (aq) ???

Mg (s) + NaCl (aq) ???

Reactivity Series

Mg (s) + CuCl2 (aq) MgCl2 (aq) + Cu (s)

Mg (s) + NaCl (aq) ???

Reactivity Series

Mg (s) + CuCl2 (aq) MgCl2 (aq) + Cu (s)

Mg (s) + NaCl (aq) NR

Reactivity Series

Mg (s) + CuCl2 (aq) MgCl2 (aq) + Cu (s)

Mg (s) + NaCl (aq) NR

Activity Series:

Reactivity Series

Mg (s) + CuCl2 (aq) MgCl2 (aq) + Cu (s)

Mg (s) + NaCl (aq) NR

Activity Series: Na > Mg > Cu

Reactivity Series

Some halogens make better reducing agents than other halogens. (In other words, some halogens are oxidized easier.)

Let’s look at two reactions:

F2 (g) + NaCl (aq) ???

Br2 (l) + NaCl (aq) ???

Reactivity Series

Let’s look at two reactions:

F2 (s) + 2 NaCl (aq) 2 NaF + Cl2

Br2 (s) + NaCl (aq) ???

Reactivity Series

Let’s look at two reactions:

F2 (s) + 2 NaCl (aq) 2 NaF + Cl2

Br2 (s) + NaCl (aq) NR

Reactivity Series

Let’s look at two reactions:

F2 (s) + 2 NaCl (aq) 2 NaF + Cl2

Br2 (s) + NaCl (aq) NR

Activity Series:

Reactivity Series

Let’s look at two reactions:

F2 (s) + 2 NaCl (aq) 2 NaF + Cl2

Br2 (s) + NaCl (aq) NR

Activity Series: F > Cl > Br

What does that resemble?

Halogens

FClBrI

Most Reactive

Least Reactive