Ch07 Final

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John E. McMurry Robert C. Fay

Lecture NotesAlan D. EarhartSoutheast Community College Lincoln, NE

General Chemistry: Atoms First

Chapter 7Reactions in Aqueous Solution

Copyright 2010 Pearson Prentice Hall, Inc.

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Copyright 2010 Pearson Prentice Hall, Inc. Chapter 7/2

Some Ways That Chemical

Reactions Occur

Precipitation Reactions: Processes in which soluble

ionic reactants yield an insoluble solid product that

falls out of solution.

2KNO3(aq) + PbI

2(s)Pb(NO3)2(aq) + 2KI(aq)

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Reactions Occur

Acid-Base Neutralization Reactions: Processes in

which an acid reacts with a base to yield water plus an

ionic compound called a salt.

H2O(l) + NaCl(aq)HCl(aq) + NaOH(aq)

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Reactions Occur

Oxidation-Reduction (Redox) Reactions: Processes

in which one or more electrons are transferred

between reaction partners (atoms, molecules, or ions).

MgCl2(aq) + H2(g)Mg(s

) + 2HCl(aq)

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Electrolytes in Aqueous

Solution

Electrolytes: Substances which dissolve in water to

produce conducting solutions of ions.H2O

Na1+(aq) + Cl1-(aq)NaCl(s)

Nonelectrolytes: Substances which do not produce

ions in aqueous solutions.H2O

C12H22O11(aq)C12H22O11(s)

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Solution

Weak Electrolytes: Compounds that dissociate to a

smallextent into ions when dissolved in water.

H1+

(aq) + CH3CO21-

(aq)CH3CO2H(aq)

Strong Electrolytes: Compounds that dissociate to a

large extent into ions when dissolved in water.

H1+(aq) + Cl1-(aq)HCl(g)H2O

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Solution

StrongAcids: hydrochloric acid, hydrobromic acid,

hydroiodic acid, perchloric acid, nitric acid, sulfuric acid.

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Solution

Ionic compounds

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Solution

Weakacids

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Chapter 7/11


Solution

Molecular compounds (other than any strong or weak

electrolytes)

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Solution

Dissociation Equations

Fe3+

(aq) + 3Br1-

(aq)FeBr3(s

)

H2O

2Na1+

(aq) + SO42-

(aq)Na2SO4(s)

H2O

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Aqueous Reactions and Net

Ionic Equations

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

MolecularEquation: All substances in the chemical

equation are written using their complete formulas as

if they were molecules.

strong electrolytes precipitate

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Ionic Equations

Ionic Equation: All of the strong electrolytes are

written as ions.

2K1+(aq) + 2NO31- (aq) + PbI2(s)

Pb2+(aq) + 2NO31- (aq) + 2K1+(aq) + 2I1-(aq)

2KNO3(aq)

Pb(NO3)2(aq) 2KI(aq)

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Ionic Equations

Spectator Ions: Ions that undergo no change during

the reaction and appear on both sides of the reaction

arrow.

2K1+(aq) + 2NO31- (aq) + PbI2(s)

Pb2+(aq) + 2NO31- (aq) + 2K1+(aq) + 2I1-(aq)

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Ionic Equations

PbI2(s)Pb2+(aq) + 2I1-(aq)

Net Ionic Equation: Only the ions undergoing change

are shown.

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Precipitation Reactions and

Solubility Guidelines

Solubility: States how much of a compound will

dissolve in a given amount of solvent at a given

temperature.

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1. A compound is probably soluble if it contains one of

the following cations:

Group 1A cation: Li1+, Na1+, K1+, Cs1+

Ammonium ion: NH41+

2. A compound is probably soluble if it contains one of

the following anions:

Halide: Cl1-, Br1-, I1-

exceptAg1+

, Hg22+

, and Pb2+

compounds Nitrate (NO3

1-), perchlorate (ClO41-), acetate (CH3CO2

1-),

sulfate (SO42-)

exceptBa2+, Hg22+, and Pb2+ sulfates

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Write the molecular, ionic, and net ionic equations for

the reaction that occurs when aqueous solutions of

AgNO3 and Na2CO3 are mixed.

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Chapter 7/20



Write the chemical formulas of the products (useproper ionic rules).

Ag2CO3AgNO3(aq) + Na2CO3(aq) + NaNO3

CB +ADAB + CD

double replacement reaction




1.

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MolecularEquation: Balance the equation andpredict the solubility of each possible product.

Ag2CO3(s) + 2NaNO3(aq)2AgNO3(aq) + Na2CO3(aq)

Contains a group 1A cation.

Neither the cation nor the

anion is in the solubility list.




2.

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Ionic Equation: Dissociate the soluble ioniccompounds.




3.

Ag2CO3(s) + 2Na1+(aq) + 2NO3

1-(aq)

2Ag1+

(aq) + 2NO31-

(aq) + 2Na1+

(aq) + CO32-

(aq)

2NaNO3(aq)

2AgNO3(aq) Na2CO3(aq)

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Net Ionic Equation: Eliminate the spectator ions fromthe ionic equation.

Ag2CO3(s)2Ag1+(aq) + CO3

2-(aq)

4.

Ag2CO3(s) + 2Na1+

(aq) + 2NO31-

(aq)

2Ag1+(aq) + 2NO31- (aq) + 2Na1+(aq) + CO3

2-(aq)

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Acids, Bases, and

Neutralization Reactions

H3O1+(aq) + Cl1-(aq)HCl(aq) + H2O(aq)

Acid (Arrhenius): A substance that dissociates in

water to produce hydrogen ions, H1+:

H1+(aq) + A1-(aq)HA(aq)

In water, acids produce hydronium ions, H3O1+:

H1+(aq) + Cl1-(aq)HCl(aq)

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Acids, Bases, and


Ammonia, commonly called ammonium hydroxide is

a base:

M1+(aq) + OH1-(aq)MOH(aq)

Na1+(aq) + OH1-(aq)NaOH(aq)

Base (Arrhenius): A substance that dissociates in

water to produce hydroxide ions, OH1-:

NH41+(aq) + OH1-(aq)NH3(aq) + H2O(aq)

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Acids, Bases, and


Weak acids and weak bases are weak electrolytes.

Strong acids and strong bases are strong electrolytes.

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ateic

iteous

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Acids, Bases, and

Neutralization ReactionsBinary Acids

HCl hydrochloric acid

HBr hydrobromic acid

HF hydrofluoric acid

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Acids, Bases, and


MA + H2OHA + MOH

These acid-base neutralization reactions are double-

replacement reactions just like the precipitation

reactions:

or

MA + HOHHA + MOH

WaterAcid Base Salt

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Write the chemical formulas of the products (use

proper ionic rules for the salt).

1.

Acids, Bases, and



the reaction of aqueous HBr and aqueous Ba(OH)2.

H2OHBr(aq) + Ba(OH)2(aq) + BaBr2

SaltAcid Base Water

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MolecularEquation: Balance the equation and

predict the solubility of the salt in the products.

2.

Acids, Bases, and




2H2O(l) + BaBr2(aq)2HBr(aq) + Ba(OH)2(aq)

Use the solubility rules.

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Ionic Equation: Dissociate a strong acid and the

soluble ionic compounds.

3.

Acids, Bases, and




2H2O(l) + Ba2+(aq) + 2Br1-(aq)

2H1+(aq) + 2Br1-(aq) + Ba2+(aq) + 2OH1-(aq)

BaBr2(aq)

2HBr(aq) Ba(OH)2(aq)

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2H2O(l) + Ba2+(aq) + 2Br1-(aq)

Acids, Bases, and




Net Ionic Equation: Eliminate the spectator ions from

the ionic equation.

4.

2H1+(aq) + 2Br1-(aq) + Ba2+(aq) + 2OH1-(aq)

or

H2O(l)H1+(aq) + OH1-(aq)

2H2O(l)2H1+(aq) + 2OH1-(aq)

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Acids, Bases, and



the reaction of aqueous NaOH and aqueous HF.

Write the chemical formulas of the products (use

proper ionic rules for the salt).

1.

SaltAcid Base Water

H2OHF(aq) + NaOH(aq) + NaF

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Acids, Bases, and




MolecularEquation: Balance the equation and

predict the solubility of the salt in the products.

2.

H2O(l) + NaF(aq)HF(aq) + NaOH(aq)

Use the solubility rules.

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Acids, Bases, and




Ionic Equation: Dissociate a strongacid and the

soluble ionic compounds.

3.

H2O(l) + Na1+(aq) + F1-(aq)HF(aq) + Na1+(aq) + OH1-(aq)

NaF(aq)

NaOH(aq)

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Acids, Bases, and




Net Ionic Equation: Eliminate the spectator ions from

the ionic equation.

4.

H2O(l) + Na1+(aq) + F1-(aq)HF(aq) + Na1+(aq) + OH1-(aq)

H2O(l) + F1-(aq)HF(aq) + OH1-(aq)

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Chapter 7/38

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Oxidation-Reduction (Redox)

Reactions

2Fe2O3(s)4Fe(s) + 3O2(g)Rusting of iron:

an oxidation of Fe

4Fe(s) + 3CO2(g)2Fe2O3(s) + 3C(s)Manufacture of iron:

a reduction of Fe

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Reactions

Oxidation: The loss of one or more electrons by a

substance, whether element, compound, or ion.

Reduction: The gain of one or more electrons by a

substance, whether element, compound, or ion.

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Reactions

1. An atom in its elemental state has an oxidation

number of 0.

Rules for Assigning Oxidation Numbers

Oxidation Number (State): A value which indicates

whether an atom is neutral, electron-rich, or electron-

poor.

Na H2 Br2 S Ne

Oxidation number 0

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Reactions

2. An atom in a monatomic ion has an oxidation

number identical to its charge.

Na1+

+1

Ca2+

+2

Al3+

+3

Cl1-

-1

O2-

-2

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Reactions

b) Oxygen usuallyhas an oxidation number of -2.

H O1-

-2+1

HH Ca

-1-1 +2

3. An atom in a polyatomic ion or in a molecular

compound usually has the same oxidation number

it would have if it were a monatomic ion.

a) Hydrogen can be either +1 or -1.

OH O

-1+1 -1

HH O

+1+1 -2

H

+1

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Reactions

H Cl

+1 -1

c) Halogens usuallyhave an oxidation number of -1.3.

ClCl O

+1+1 -2

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Reactions

Cr2O72-

-2+1 x

4. The sum of the oxidation numbers is 0 for a neutral

compound and is equal to the net charge for a

polyatomic ion.

x = +6

2(x) + 7(-2) = -2 (net charge)

H2SO3

x -2

x = +4

2(+1) + x + 3(-2) = 0 (net charge)

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Identifying Redox Reactions

Causes oxidation

Gains one or more electrons Undergoes reduction

Oxidation number of atom decreases

Causes reduction

Loses one or more electrons

Undergoes oxidation

Oxidation number of atom increases

Oxidizing Agent

Reducing Agent

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2Fe23O2(g)+4Fe(s) O3(s)

-20

reduction

oxidation

+30

Oxidizing Agent

Reducing Agent

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3


4Fe(s)C(s) +2Fe2O3 + 3 (g)(s) O2C

oxidation

+40

-2+3

reductionOxidizing Agent

Reducing Agent

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The Activity Series of the

Elements

2Ag1+(aq) + Cu(s)2Ag(s) + Cu2+(g)

Cu2+(aq) + 2Ag(s)Cu(s) + 2Ag1+(g)

Which one of these reactions will occur?

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Chapter 7/50

The Activity Series of the

Elements

The elements that are

higher up in the table

are more likely to be

oxidized.

Thus, any element

higher in the activity

series will reduce theion of any element

lower in the activity

series.

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Balancing Redox Reactions:

The Half-Reaction Method

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Balance the following net ionic equation in acidic

solution:

Cr3+(aq) + IO31-(aq)I1-(aq) + Cr2O7

2-(aq)

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Write the two unbalanced half-reactions.

IO31-(aq)I1-(aq)

Cr3+(aq)Cr2O72-(aq)

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Multiply each half-reaction by a factor to make the

electron count the same in both half-reactions.

IO31-(aq) + 6H1+(aq)6e- + 3H2O(l) + I

1-(aq)

2Cr3+(aq) + 7H2O(l) + 6e-14H1+(aq) + Cr2O7

2-(aq)

oxidation:

reduction:

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Add the two balanced half-reactions together and

cancel species that appear on both sides of the

equation.

IO31-(aq) + 6H1+(aq)6e- + 3H2O(l) + I

1-(aq)

2Cr3+(aq) + 7H2O(l) + 6e-14H1+(aq) + Cr2O7

2-(aq)

oxidation:

reduction:

IO31-(aq) + 2Cr3+(aq) + 4H2O(l)

8H1+(aq) + I1-(aq) + Cr2O72-(aq)

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MnO2(s) + BrO31-(aq)MnO4

1-(aq) + Br1-(aq)



Balance the following net ionic equation in basic

solution:

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Write the two unbalanced half-reactions.

BrO31-(aq)Br1-(aq)

MnO2(s)MnO41-(aq)

B l i R d R i

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Balance both half-reactions for all atoms except O and

H.

BrO31-(aq)Br1-(aq)

MnO2(s)MnO41-(aq)

B l i R d R ti

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BrO31-(aq) + 6H1+(aq)3H2O(l) + Br

1-(aq)

MnO2(s) + 2H2O(l)4H1+(aq) + MnO4

1-(aq)

Balance each half-reaction for O by adding H2O, and

then balance for H by adding H1+.

B l i R d R ti

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BrO31-(aq) + 6H1+(aq) + 6e-3H2O(l) + Br

1-(aq)

MnO2(s) + 2H2O(l)3e- + 4H1+(aq) + MnO4

1-(aq)

Balance each half-reaction for charge by adding

electrons to the side with greater positive charge.

B l i R d R ti

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Multiply each half-reaction by a factor to make the

electron count the same in both half-reactions.

2

BrO31-(aq) + 6H1+(aq) + 6e-3H2O(l) + Br

1-(aq)

MnO2(s) + 2H2O(l)3e- + 4H1+(aq) + MnO4

1-(aq)

B l i R d R ti

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2MnO2(s) + H2O(l) + BrO31-(aq)

2H1+(aq) + 2MnO41-(aq) + Br1-(aq)



BrO31-(aq) + 6H1+(aq) + 6e-3H2O(l) + Br

1-(aq)

2MnO2(s) + 4H2O(l)6e- + 8H1+(aq) + 2MnO4

1-(aq)

Add the two balanced half-reactions together and

cancel species that appear on both sides of the

equation.

B l i R d R ti

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Since the reaction occurs in a basic solution,

neutralize the excess H1+ by adding OH1- and cancel

any water (if possible).

2MnO2(s) + H2O(l) + BrO31-(aq) + 2OH1-(aq)

2OH1-(aq) + 2H1+(aq) + 2MnO41-(aq) + Br1-(aq)

2H2O

2MnO2(s) + BrO31-(aq) + 2OH1-(aq)

H2O(l) + 2MnO41-(aq) + Br1-(aq)

R d St i hi t

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Redox Stoichiometry

Titration: A procedure for determining the concentration

of a solution by allowing a carefully measured volume to

react with a solution of another substance (the standard

solution) whose concentration is known.

5H2C2O4(aq) + 2MnO41-(aq) + 6H1+(aq)

10CO2(g) + 2Mn2+(aq) + 8H2O(l)

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Chapter 7/66

R d St i hi t

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Redox Stoichiometry

5H2C2O4(aq) + 2MnO41-(aq) + 6H1+(aq)

10CO2(g) + 2Mn2+(aq) + 8H2O(l)

A solution is prepared with 0.2585 g of oxalic acid,

H2C2O4. 22.35 mL of an unknown solution of potassium

permanganate are needed to titrate the solution. What is

the concentration of the potassium permanganate

solution?

Moles ofH2C2O4Mass ofH2C2O4

Moles ofKMnO4Molarity ofKMnO4

Mole Ratio Molarity of

KMnO4

Molar Mass

of H2C2O4

R d St i hi t

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Redox Stoichiometry

5H2C2O4(aq) + 2MnO41-(aq) + 6H1+(aq)

10CO2(g) + 2Mn2+(aq) + 8H2O(l)

Moles of H2C2O4 available:

90.04 g

1 mol= 0.002871 mol H2C2O4

0.2585 g H2C2O4

Moles of KMnO4 reacted:

5 mol H2C2O4

2 mol KMnO4= 0.001148 mol KMnO4

0.002871 mol H2C2O4

x

x

Redo Stoichiometr

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1 L

1000 mL

Redox Stoichiometry

5H2C2O4(aq) + 2MnO41-(aq) + 6H1+(aq)

10CO2(g) + 2Mn2+(aq) + 8H2O(l)

Concentration of KMnO4 solution:

= 0.05136 M KMnO422.35 mL

x0.001148 mol KMnO4

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