Today’s Objectives:

1. Define oxidizing agent and reducing agent

2. Identify electron transfer, oxidizing agents, and reducing agents in REDOX reactions that occur everyday in both living and non-living systems.

Section 13.2 (pp. 568-582)

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▫ Review: “LEO the lion says GER”

Loss of electrons = entity being oxidized

Gain of electrons = entity being reduced

Chemists don’t usually say “the reactant being oxidized” or “the reactant being reduced”

Instead they use the terms OXIDIZING AGENT (OA) and REDUCING AGENT (RA)

OXIDIZING AGENT: causes oxidation by removing (gaining) electrons from another substance in a redox reaction, therefore the oxidizing agent is being reduced.

REDUCING AGENT: causes reduction by donating (losing) electrons to another substance in a redox reaction, therefore the reducing agent is being oxidized.

What does this mean? Let’s revisit zinc reacting with and hydrochloric acid.

Which reactant was reduced? Which was oxidized?

Which is the Oxidizing Agent (OA)? Which is the Reducing Agent (RA)

Redox Terms

Zn(s) Zn 2+(aq) + 2 e-

2 H+(aq) + 2 e-

H2 (g)

Reducing Agent

Oxidizing Agent

LEO = Oxidized

GER = Reduced

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OIL RIGOxidation is Loss

Reduction is Gain

▫ Silver ions were reduced to silver metal by reaction with copper metal. Simultaneously, copper metal was oxidized to copper(II) ions by reaction with silver ions.

▫ If Ag+(aq) is reduced it’s the:

▫ If Cu(s) is oxidized it is the:

Redox Terms

REDUCING AGENT (RA)

OXIDIZING AGENT (OA)

It is important to note that oxidation and reduction are processes, and oxidizing agents and reducing agents are substances.

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• Summary so far:

▫ The substance that is reduced (gains electrons) is also known as the oxidizing agent

▫ The substance that is oxidized (loses electrons) is also knows as the reducing agent

Redox Terms

• Question: If a substance is a very strong oxidizing agent, whatdoes this mean in terms of electrons?

The substance has a very strong attraction for electrons.

• Question: If a substance is a very strong reducing agent, whatdoes this mean in terms of electrons?

The substance has a weak attraction for its electrons, which are easily removed

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Figure 3 – p. 569

Reduction Oxidation

• Historically, the formation of a metal from its “ore” (or oxide)

▫ i.e. nickel(II) oxide is reduced by hydrogen gas to nickel metal

NiO(s) + H2(g) Ni(s) + H2O(l)

Ni +2 Nio

• A gain of electrons occurs (so the entity becomes more negative)

• Electrons are shown as the reactant in the half-reaction

• A species undergoing reduction will be responsible for the oxidation of another entity, therefore is classified as an oxidizing agent (OA)

REDOX Reactions … so far

• Historically, reactions with oxygen

▫ i.e. iron reacts with oxygen to produce iron(III) oxide

4 Fe(s) + O2(g) Fe2O3(s)

Fe 0 Fe+3

• A loss of electrons occurs (so the entity becomes more positive)

• Electrons are shown as the product in the half-reaction

• A species undergoing oxidation will be responsible for the reduction of another entity, therefore is classified as an reducing agent (RA)

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Today’s Objectives:

1. Define oxidizing agent, reducing agent, and half-reaction

2. Compare the relative strengths of oxidizing and reducing agents from empirical data.

3. Predict the spontaneity of a REDOX reaction based on a REDOX table, and compare predictions to experimental results.

Section 13.2 (pp. 568-582)

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Quick REDOX Review

• REDOX reaction explained as a transfer of valence electrons from one substance to another (i.e. two entities involved in e – transfer)

• oxidation & reduction reactions are processes

• oxidizing & reducing agents are substances

• RA loses e – (weak attraction) causing reduction by being oxidized (OIL)

• OA gains e – (strong attraction) causing oxidation by being reduced (RIG)

• e – transfer from RA to OA

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REDOX Table• Used to indicate the relative strengths of OA and RA

• Consider the reactivity of metal ions in Table 1 – p. 569

▫ metal ions (OA) gain elections to oxidize metals (RA)

▫ Based on evidence collected, we can rank the ability of the metal ion to react with the metals.

▫ The most reactive metal ion, Ag+(aq), has the greatest tendency to

gain electrons, unlike the Zn2+(aq), which shows no tendency to

gain electrons in the combinations tested.

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Table 1 – p. 569

Ions Ag+(aq) Cu2+

(aq) Pb2+(aq) Zn2+

(aq)

reacted with Cu(s), Pb(s), Zn(s) Pb(s), Zn(s) Zn(s) none

number of reactions

3 2 1 0

reactivity order Most Least

• By convention, table written as reduction half reactions, therefore all reactants will be OA (i.e. gain e–)▫ list in decreasing order of OA strength

Ag+(aq) + e-

Ag(s)

Cu2+(aq) + 2 e-

Cu(s)

Pb2+(aq) + 2 e-

Pb(s)

Zn2+(aq) + 2 e-

Zn(s)

OA + n e- RA

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REDOX Table

SOA

SRA

⇌

⇌

⇌

⇌

⇌

REDOX Spontaneity Rule

• A reaction is considered spontaneous if it occurs on its own

• The table of relative strengths of OA and RA with reduction half reactions is useful in predicting the spontaneity of a reaction

▫ Spontaneous REDOX reactions occur only if the OA is above the RA

If OA is below the RA, then the reaction is considered non-spontaneous.

A reaction will be spontaneous if on a redox table:

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OAabove = spont rxn

RA

RAabove= non-spont rxn

OA

Figure 5 – p. 572

• Consider the following experimental information and add reduction half-reactions to the REDOX table created earlier.

Au3+(aq) + 3 e- ⇌ Au(s)

Hg2+(aq) + 2 e- ⇌ Hg(s)

Ag+(aq) + e- ⇌ Ag(s)

Cu2+(aq) + 2 e- ⇌ Cu(s)

Pb2+(aq) + 2 e- ⇌ Pb(s)

Zn2+(aq) + 2 e- ⇌ Zn(s)

Hg2+(aq) Cu2+

(aq) Ag+(aq) Au3+

(aq)

Hg(s) ✗ ✗ ✗ ✓

Cu(s) ✓ ✗ ✓ ✓

Ag(s) ✓ ✗ ✗ ✓

Au(s) ✗ ✗ ✗ ✗

Hg2+(aq) Cu2+

(aq) Ag+(aq) Au3+

(aq)

Hg(l) ✗ ✗ ✗ ✓

Cu(s) ✓ ✗ ✓ ✓

Ag(s) ✓ ✗ ✗ ✓

Au(s) ✗ ✗ ✗ ✗

Example: Building REDOX Tables

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SOA

SRASRA

SOA

YES! Because of the

spontaneity rule!

Check p. 7 of the data

booklet. Does this ranking

order match?

• The spontaneity rule can also be used to generate REDOX tables

▫ Use the following information to create a table of reduction half reactions

3 Co 2+(aq) + 2 In(s) 2 In 3+

(aq) + 3 Co(s)

Cu 2+(aq) + Co(s) Co 2+

(aq) + Cu(s)

Cu 2+(aq) + Pd(s) no reaction

Pd2+(aq) + 2 e- ⇌ Pd(s)

Cu2+(aq) + 2 e- ⇌ Cu(s)

Co2+(aq) + 2 e- ⇌ Co(s)

In3+(aq) + 3 e- ⇌ In(s)

Sample Problem 13.4 – p. 573

SOA

SRA

OA

OA

OA

RA

RA

RA

Cu2+

In(s)

Co2+ Co(s)

Pd(s)

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Determine the relative position of REDOX pairs based on reaction

spontaneityFigure 6 – p. 573

• Use the following information to create a table of reduction half reactions

2 A 3+(aq) + 3 D(s) 3 D2+

(aq) + 2 A(s)

G + (aq) + D(s) no reaction

3 D 2+(aq) + 2 E(s) 3 D(s) + 2 E3+

(aq)

G +(aq) + E(s) no reaction

A3+(aq) + 3 e- ⇌ A(s)

D2+(aq) + 2 e- ⇌ D(s)

E3+(aq) + 3 e- ⇌ E(s)

G +(aq) + e- ⇌ G(s)

Example: Building REDOX Tables

OA

OA

OA

RA

RA

RA

G+

D(s)

A3+

E(s)OA RA

D2+

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SOA

SRA

• So far examples include OA that are metal ions and RA that are metal atoms.

• What else could gain or lose electrons?

▫ Non-metal atoms gain electrons – OA i.e. Cl2(g) + 2e– 2 Cl–

(aq)

Cl–(aq) could act as a Reducing Agent

▫ Non-metal ions lose electrons – RA i.e. 2 Br–(aq) Br2(l) + 2 e–

Br2(l) could act as an Oxidizing Agent

• OA tend to be metal ions and non-metal atoms

• RA tend to be metal atoms and non-metal ions

• Are there any entities that could act as both OA or RA?

▫ Multivalent metals

REDOX Tables Trends

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– p. 574

Homework

• Practice Qs – p. 571 #1-10

• Lab Exercise 13.A – p. 572▫ DUE: Thursday, October 29

• Practice Qs – p. 573 #11-14; p. 574 #15-24

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Today’s Objectives:

1. Predict REDOX reactions

2. Define disproportionation

3. Identify electron transfer, oxidizing agents, and reducing agents in REDOX

reactions that occur everyday in both living and non-living systems.

Section 13.2 (pp. 568-582)

16

• Use the following information to create a table of reduction half reactions

Ag(s) + Br2(l) AgBr(s)

Ag(s) + I2(s) no evidence of reaction

Cu2+(aq) + I–

(aq) no redox reaction

Br2(l) + Cl–(aq) no evidence of reaction

Cl2(g) + 2 e– 2Cl–

(aq)

Br2(l) + 2 e– 2Br–

(aq)

Ag+(aq) + 1 e–

Ag(s)

I2(s) + 2 e– 2I–

(aq)

Cu2+(aq) + 2 e–

Cu(s)

Practice Question - p. 573 #14

SOA

SRA

OA

OA

OA

RA

RA

RA I2(s)

Cu2+(aq)

Cl–(aq)

Ag(s)

OA RA

Br2(l)

I–(aq)

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⇌

⇌⇌⇌⇌

1. List all the entities that are present▫ Refer to Table 6 – p. 575

▫ In solutions, molecules and ions behave independently of each other.

Example: copper metal placed into an acidic solution

of potassium permanganate

Predicting REDOX Reactions

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With the knowledge of REDOX reactions you will be responsible for determining if a reaction will spontaneously occur and its corresponding reaction equation.

Cu(s) K+(aq) MnO4

–(aq) H +

(aq) H2O(l)

2. Determine all possible OA and RA

▫ This is a crucial step!! Consider:

Combinations

MnO4-(aq) is only an OA in an acidic solution

Indicate this pair by drawing an arc between the permanganate and hydrogen ion

Species that can act as OA or RA

Label both possibilities in your list

19

Predicting REDOX Reactions

Cu(s) K+(aq) MnO4

–(aq) H +

(aq) H2O(l)

OA

OA

RARA

OAOA

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Predicting REDOX Reactions3. Identify the SOA and SRA using the REDOX table in the data booklet

• Predict the reaction spontaneity

SOA > SRA ⇒ spont.

4. Show the reduction half reactions and balance

• Copy the SOA equation directly from table

• Read the SRA equation from right to left

Cu(s) K+(aq) MnO4

–(aq) H +

(aq) H2O(l)

OA

OA

RARA

OAOA

SOA

SRA

MnO4–

(aq) + 8H+(aq) + 5e–

Mn2+(aq) + H2O(l)

Cu(s) Cu2+(aq) + 2e–

2 [ ]

5 [ ]

2 MnO4–

(aq) + 16H+(aq) + 5Cu(s) 2Mn2+

(aq) + 2H2O(l) + 5Cu2+(aq)

spont.

• potassium permanganate solution is slowly poured into

acidified iron(II) sulfate solution

• Experimentally when these solutions are mixed the purple color of the permanganate ion disappears as it is reacted. Also a diagnostic test of the pH would indicate hydrogen ions reacting if the pH increased.

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Sample Problem 13.5 – p. 576

SOA

SRA

spont.

Figure 9 – p. 576

Could copper pipe be used to transport a hydrochloric acid solution?

Since the reaction is nonspontaneous, it should be possible to use a copper pipe to carry hydrochloric acid.

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Communication Example 1 – p. 577

Figure 10 – p. 577

• The REDOX electron transfer reactions covered so far have one reactant (OA) that removes electrons from a second reactant (RA) if a spontaneous reaction occurs.

• Although the OA and RA are usually different entities, this is not a requirement.

• A reaction is which a species is both oxidized and reduced is called disproportionation

▫ aka autoxidation or self oxidation-reduction

▫ occurs when a substance can act as either an OA or RA

Disproportionation

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Example: Will a spontaneous reaction occur as a result of an electron transfer from one iron(II) ion to another iron (II) ion when two iron (II) solutions are combined?

Use the REDOX table and spontaneity rule, which indicates that iron(II) as an OA is below iron(II) as a RA, therefore the reaction is non-spontaneous and will not occur.

Disproportionation

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non spont.

Example: Will a spontaneous reaction occur as a result of an electron transfer from one

copper(I) ion to another copper (I) ion?

Cu+(aq) + 1 e-

Cu(s)

Cu+(aq) Cu2+

(aq) + 1 e-

2 Cu+(aq) Cu2+

(aq) + Cu(s)

▫ Use the REDOX table and spontaneity rule, which indicates that copper (I) as an OA is above copper (I) as a RA, therefore an aqueous solution of copper (I) ions will spontaneously, but slowly, disproportionate into copper (II) ions and copper metal.

Disproportionation

25

Communication Examples 2 – p. 578

spont.

• Suppose the REDOX table does not provide the half-reaction equations needed

▫ Use your knowledge about constructing half-reactions to create a REDOX equation

Recall the summary on page 567 for writing half-reaction equations.

▫ Consider the main starting materials and reaction conditions (acidic or alkaline)

Create a skeleton equation showing only the main reactants and products

Examine individual balanced half-reaction equations to determine the details of the overall REDOX reaction equation

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Predicting REDOX Reactions by Constructing Half-Reactions

• A person suspected of being intoxicated uses a breathalyzer device and the alcohol in their breath reacts with an acidic dichromate ion solution to produce acetic acid (ethanoic acid) and aqueous chromium(III) ions. Predict the balanced REDOX reaction equation.

• Create a skeleton equation from the information provided:

• Separate the entities into the start of two half-reaction equations

• Apply strategies for writing half reactions (p. 567)

• Now, balance the electrons lost and gained, and add the half reactions. Cancel the electrons and anything else that is exactly the same on both sides of the equation.

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Sample Problem 13.6 – p. 580

• Permanganate ions and oxalate ions react in a basic solution to produce

carbon dioxide and manganese (IV) oxide

• Create a skeleton equation from the information provided:

• Separate the entities into the start of two half-reaction equations

• Apply strategies for writing half reactions (p. 567)

• Now, balance the electrons lost and gained, and add the half reactions. Cancel the electrons and anything else that is exactly the same on both sides of the equation.

• Basic solution so add OH-(aq) to both sides to equal the number of H+

(aq) present.

• Cancel equal amounts of H2O(l) from both sides.

28

Communication Example 3 – p. 581

1. Use the information provided to start two half-reaction equations.

2. Balance each half-reaction equation.

3. Multiply each half-reaction by simple whole numbers to balance electrons lost and gained.

4. Add the two half-reaction equations, cancelling the electrons and anything else that is exactly the same on both sides of the equation.

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SummaryPredicting REDOX Reactions by

Constructing Half-Reaction Equationsp. 581

• The smell of a skunk is caused by a thiol compound (R-SH).To deodorize a pet sprayed by a skunk, you need to convertthe smelly thiol to an odourless compound.

• Hydrogen peroxide in a basic solution (usually sodiumbicarbonate) acts as an oxidizing agent to change the thiol to adisulfide compound (RS-SR), which is odourless.

Figure 8 – p. 575

REDOX in Living Organisms

30

• Predict the products of the reaction of sodium metal with water.

Na(s) H2O(l)

2 H2O(l) + 2 e–H2(g) + 2 OH–

(aq)

2 [ Na(s) Na+(aq) + e– ]

2 H2O(l) + 2 Na(s) 2 Na+(aq) + H2(g) + 2 OH–

(aq)

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Investigation 13.3 – p. 581

OASOA

RARASRA

spont.

Brainiacs!

Slow Motion

VIDEOS:Na in Water

Na Properties

Cesium

Determine presence with the hydrogen pop test

Diagnostic Test?

Examine pH for an alkaline

solution

Homework

• Practice Qs – p. 575 #25; p. 579 #25-30;

p. 579 #26-30; p. 581 #31-33

• Section 13.2 Review – p. 582 #1-18

• Section 13.2 Extra Exercises handout

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