chapter 4: types of chemical reactions and solution...

Chapter 4: Types of Chemical

Reactions and Solution Stoichiometry

A bag of mostly water

- Star Trek -

Collision

Rareness No mobility

Solution is the solution.

Water, the Common Solvent

Solution : a homogenous mixture of 2 or more substances

Solute : the substance(s) present in the smaller amount(s)

Solvent : the substance present in the larger amount

Solution Solvent Solute

Soft drink (l) H2O Sugar, CO2

Air (g) N2 O2, Ar, CH4

Soft Solder (s) Pb Sn

Aqueous

Solution

A bag of mostly water

- Star Trek -

Plenty of water

-> Plenty of chemical reactions

-> Plenty of diversified matters

Why water?

Water, the Common SolventWhy water ? • Because water can dissolve many chemical substances.

• The most “Universal Solvent” known.

* Universal solvent: A substance that has the ability to dissolve both bases and acids.

Polarity of water which allows it to interact ionic and nonionic substances.

Hydration : the process in which an ion is surrounded by water molecules

arranged in a specific manner.

NaCl

EthanolLike dissolves Like.

And For Life

Range of temperatures in which water is

maintained in a liquid state (0oC ~ 100oC).

Different density of the liquid and solid

state, which allows ice to float on liquid

water.

Dissolving

The Nature of Aqueous Solutions:

Strong and Weak Electrolytes

Arrhenius' postulation : the extent to which a

solution can conduct an electric current depend

directly on the number of ions presnet in the solution

(as usual, the postulation was not accepted in the

scientific society at the time of 1880s, but later

(1890s) accepted)

Solute

Electrolyte : a substance that, when

dissolved in water, results in a solution that

can conduct electricity.

Nonelectrolyte : a substance that, when

dissolved, results in a solution that does

not conduct electricity.

Electric conductivity of a solution

Nonelectrolyte

solution

Weak

electrolyte

solution

Strong

electrolyte

solution



Strong electrolytes - 100% dissociation occurs to

produce cations and anions when they are

dissolved in a solvent

Ionic compunds

Strong acids - dissociate completely to

produce H+ in solution

NaCl(s) → Na+(aq) + Cl-(aq)H2O

HCl → H+(aq) + Cl-(aq)

H2O

HNO3 → H+(aq) + NO3-(aq)

H2O

H2SO4 → H+(aq) + HSO4-(aq)

H2O

Strong bases - react completely with water to

give OH- ions.

NaOH → Na+(aq) + OH-(aq)

H2O

KOH → K+(aq) + OH-(aq)

H2O

(Sugar)



Weak electrolytes - not 100% dissociation occurs

when they are dissolved in a solvent

Weak acids - dissociate to a slight extent to give

H+ in solution

CH3COOH(aq) → H+(aq) + CH3COO-(aq)←

Weak bases - react only slightly with water to

give OH- ions

NH3(aq) + H2O(l)

←→ NH4+(aq) + OH-(aq)

Nonelectrolytes - no dissociation occurs when

they are dissolved in a solvent

C12H22O11 → C12H22O11(aq)

H2O

completely dissolve but no dissociation

(Sugar)

nondissovable substances - not solutes

The Composition of SolutionsDissolving helps chemical reactions

Dissolving process – separating bulk material to each molecule or ion

Now a molecule or an ion can have chance to meet other molecules or ions to

initiate chemical reactions in aqueous solution (liquid phase).

Stoichiometric calculation in solution - must know (1) the nature of the reaction (which

chemicals are involved) (2) the amount of the chemicals (solution composition)

Expressions of a solution composition

(L)solution ofliter

(mol) solute of moles (M)Molarity

(N)Normality (m),Molality , )(fraction Mole percent, (weight) Mass , (M)Molarity A

Molarity (M) (concentration of solution) = moles of solute per volume of solution in liters:

The Composition of SolutionsEx) Molarity of a solution prepared by dissolving 1.56 g of gaseous HCl in enough

water to make 26.8 mL of solution. (HCl => 36.46 g/mol)

HCl 60.11026.8

HCl 1028.4

26.8

HCl 1028.4 Molarity

HCl 1028.446.36

1HCl 1.56

3

22

2

ML

mol

mL

mol

molg

molg

Ex) Concentration and number of moles of Cl- ions in 1.75 L of 1.0 mM ZnCl2?

-3-- Cl 105.3Cl 5.375.1Cl 2.0 molmmolLmM

ZnCl2(aq) → Zn2+(aq) + 2Cl-(aq) => Molarity of Cl- = 2.0 mM

(L)solution of volume(M)molarity (mol) solute of moles(L)solution of volume

(mol) solute of moles (M)Molarity

Ex) Typical blood serum is about 0.14 M NaCl. What volume of blood contains

1.0 mg NaCl? (NaCl => 58.45 g/mol)

mLLM

mol

molg

molmg

12.0102.1NaCl 14.0

NaCl 107.1V

NaCl 107.145.58

1NaCl 1.0

45

5

The Composition of SolutionsStandard solution - a solution whose concentration is

accurately known.

volumetric flask

Preparation of a standard aqueous solution

Common Terms of Solution Concentration

Stock - routinely used solutions prepared

in concentrated form. (stock solution)

Concentrated - relatively large ratio of

solute to solvent. (5.0 M NaCl)

Dilute - relatively small ratio of solute to

solvent. (0.01 M NaCl)

pipet

Steps for Dilution

dilution with water does not alter the numbers of

moles of solute present

2211 VMVM

The Composition of SolutionsEx) To make 1.50 L of an aqueous 0.500 M K2Cr2O7 solution, How much solid K2Cr2O7 must be

wieghed out ? (K2Cr2O7 => 294.18 g/mol)

7272

72

72

OCrK 2211

18.294OCrK 750.0

OCrK 750.0solutiom 1

OCrK 500.0solution 50.1

22

2

2

gmol

gmol

molL

molL

Ex) What volume of the above K2Cr2O7 solution must be used to prepare 1.50 L of 2.00 mM K2Cr2O7

solution ?

1.50 L

1.50 Lg ?

L ?

mLL

M

LM

00.6106.00

0.500

50.1102.00

M

VMV

VMVM

3-

3-

stock

dilutedilutestock

2211

Precipitation reaction : a reaction which results in the formation of an insoluble products,

or precipitate.

K2CrO4(aq) + Ba(NO3)2(aq) → BaCrO4(s) + 2KNO3(aq)

Types of Chemical Reactions

Acid-Base reaction : a reaction between an acid and a base.

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

Oxidation-reduction reaction : intermolecular electron transfer reaction.

CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)

hydrated methane

Precipitation reaction : a reaction which results in the formation of an insoluble products,

or precipitate.

Precipitation Reactions


Ba(NO3)2(aq) K2CrO4(aq)

K+ CrO42-Ba2+ NO3

-

Possible combinations:

Ba(NO3)2, K2CrO4, BaCrO4, KNO3

BaCrO4, K+, NO3

-


AgNO3(aq) + KCl(aq)


AgNO3, KCl, AgCl, KNO3

K+Cl- Ag+ NO3

- What is the solid product?


AgNO3(aq) + KCl(aq) → AgCl(s) + KNO3(aq)

AgNO3(aq) + KCl(aq)


AgNO3, KCl, AgCl, KNO3

K+Cl- Ag+ NO3

- What is the solid product?

KNO3(aq) + BaCl2(aq) →

Na2SO4(aq) + Pb(NO3)2(aq) →

Ex)

KOH(aq) + Fe(NO3)3(aq) →

K+(aq) + NO3-(aq) + Ba2+(aq) + 2Cl-(aq) (no reaction)

Pb(SO4)(s) + 2NaNO3(aq)

Fe(OH)3(s) + KNO3(aq)

Fe(OH)3(s) + 3KNO3(aq)3KOH(aq) + Fe(NO3)3(aq) →

Pb(NO3) (aq)

Describing Reactions in Solution

Formula equation (reactants and products as compounds)


Complete ionic equation (all strong electrolytes shown as ions)

Ba2+(aq) + 2NO3-(aq) + 2K+(aq) + CrO4

2-(aq) → BaCrO4(s) + 2K+(aq) + 2NO3-(aq)

Net ionic equation (show only components that actually react)

Ba2+(aq) + CrO42-(aq) → BaCrO4(s)

Spectator ions K+, NO3-


Formula equation : AgNO3(aq) + KCl(aq) → AgCl(s) + KNO3(aq)

Complete ionic equation :

Ag+(aq) + NO3-(aq) + K+(aq) + Cl-(aq) → AgCl(s) + K+(aq) + NO3

-(aq)

Net ionic equation : Ag+(aq) + Cl-(aq) → AgCl(s)

Spectator ions : K+, NO3-

Stoichiometry of Precipitation Reactions

Ex) Calculate the mass of PbSO4 formed when 1.25 L of 0.0500 M Pb(NO3)2 and 2.00 L of 0.0250 M

Na2SO4 are mixed.

Na2SO4(aq) + Pb(NO3)2(aq) → Pb(SO4)(s) + 2NaNO3(aq)

SO42-(aq) + Pb2+(aq) → PbSO4(s)

22 Pb 0625.0Pb 0500.025.1 molML

2

4

2

4 SO 0500.0SO 0250.000.2 molML

0.0500 mol PbSO4(s) is formed.

44 PbSO 2.151

3.303PbSO 0500.0 g

mol

gmol

Acid-Base ReactionsAcid-Base reaction : a reaction between an acid and a base.

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

Definitions

Acid Base

Arrhenius H+ producer OH- producer Defined only in aqueous solutions

Brønsted-Lowry H+ donor H+ acceptor Defined in both aqueous and non-

aqueous solutions

Lewis e- pair acceptor e- pair donor

NaOH(aq) + HCl(aq) → Na+(aq) + Cl-(aq) + H2O(l)

CH3COOH(aq) + KOH(aq) → CH3COO-(aq) + K+(aq) + H2O(l)

Arrhenius

Strong acid, base

Weak acid, baseCH3COO-(aq) + H+(aq)

OH-(aq) + K+(aq)

Net ionic equation

H+(aq) + OH-(aq) → H2O(l)

Neutralization Reaction

Acid-Base Reactions

Ex) 28.0 mL of 0.250 M HNO3 and 53.0 mL of 0.320 M KOH are mixed. 1) Number of moles of water

formed ? 2) Concentration of H+ or OH- after the completion of the reaction?


H 00.7H 250.00.28 mmolMmL

OH 0.17OH 320.00.53 mmolMmL

7.00 mmol of H2O is formed.

10.0 mmol of OH- is left after the completion.

OH 123.0)0.530.28(

OH 0.10M

mL

mmol

Acid-Base ReactionsAcid-Base Titrations

Titration : quantitative/chemical analysis used for determining the concentration of a reactant.

Acid-base titration : analysis used for determining the concentration of an acid or a base

Titrant : solution of known concentration used in titration

Analyte : substance being analyzed

Equivalence point : enough titrant added to react exactly with the analyte (moles of H+ = moles of OH-)

Endpoint : the indicator changes color so you can tell the equivalence point has been reached.

(moles of H+ ≈ moles of OH-)

Indicator

Acid-Base ReactionsAcid-Base Titrations

Ex)phenolphthalein

1.3009 g KHC8H4O4

in any volume of H2O

(KHC8H4O4 => 204.22 g/mol)

Colorless Red

Concentration of NaOH solution ?

41.20 mL NaOH solution

NaOH 1546.020.41

NaOH 106.3701 NaOH ofion Concentrat

H 106.3701

KHP 106.370122.204

1KHP 3009.1

3-

3-

3-

MmL

mol

mol

molg

molg

HC8H4O4-(aq) + OH-(aq) → H2O(l) + C8H4O4

2-(aq)


Oxidation-Reduction ReactionsOxidation-reduction reaction : intermolecular electron transfer reaction.

CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)

Na(s) Cl2(g) NaCl(s)

2Mg(s) + O2(g) → 2MgO(s)

How to know electron-transfer?

Oxidation-Reduction ReactionsOxidation state (Oxidation number)

Formal charge : the net charge of an atom when a bond is considered as a completely covalent bond.

A B

halve the shared electrons

Oxidation number : the net charge of an atom when a bond is considered as a completely ionic bond.

formal charge = net charge of an atom

A B

oxidation number = net charge of an atom

an atom having bigger electronegativity (A > B) has the shared electrons

(for A > B)

Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons.

C HH

H

H

C HH

H

H

0

0

0

00

+1

+1

+1

-4+1


Ex) Ox # of each atom ?

CO2

SF6

NO3-

O: -2, C: +4

F: -1, S: +6

O: -2, N: +5

Fe3O4

O: -2, Fe: +8/3

Oxidation-Reduction ReactionsThe Characteristics of Oxidation-Reduction Reactions

2Mg (s) + O2 (g) 2MgO (s)

0 0 -2+2

Oxidation and reduction reactions must occur simultaneously.

Number of electron loss = Number of electron gain

oxidationreduction

Mg: reductant, O2: oxidant

2Mg -> 2Mg2+ + 4e- : oxidation half-reaction

O2 + 4e- -> 2O2- : reduction half-reaction

2Mg + O2 -> 2Mg2+ + 2O2-

2Mg2+ + 2O2- -> 2MgO


CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)

-4 +1 0 +4 -2 +1 -2

CH4: reductant, O2: oxidantoxidation

reduction

CH4 -> C4+ + 4H+ + 8e- : oxidation half-reaction

2O2 + 8e- -> 4O2- : reduction half-reaction

CH4 + 2O2 -> C4+ + 2O2- + 4H+ + 2O2-

CO2H2O


Zn in CuSO4 solution

Zn(s)+CuSO4(aq)->ZnSO4(aq)+ Cu(s)

Zn(s)+Cu2+(aq) -> Zn2+(aq)+Cu(s) Zn -> Zn2+ +2e-: ox. half-rxn

Cu2+ +2e--> Cu : re. half-rxn

Zn+Cu2+->Zn2++Cu

Cu(s)+2AgNO3(aq)->Cu(NO3)2(aq)+2Ag(s)

Cu(s)+2Ag+(aq) -> Cu2+(aq)+2Ag(s)

Cu in AgNO3 solution

0 2+ 2+ 0

oxidationreduction

0 1+ 2+ 0

oxidationreduction

Cu -> Cu2+ +2e-: ox. half-rxn

2Ag++2e- -> Ag : re. half-rxn

2Ag+Cu2+->Cu2++2Ag+

Balancing Oxidation-Reduction EquationsThe Half-Reaction Method for Balancing

Oxidation-Reduction Reactions in Aqueous Solutions

Ce4+(aq) + Sn2+(aq) → Ce3+(aq) + Sn4+(aq) Is this equation correct?

Two most fundametal priciples of chemical equations :

Conservation of mass

Conservation of charge

Ce4+(aq) + e- → Ce3+(aq) (1) : reduction half-reaction

Sn2+(aq) → Sn4+(aq) + 2e- (2) : oxidation half-reaction

(1) x 2 + (2) : 2Ce4+(aq) + Sn2+(aq) → 2Ce3+(aq) + Sn4+(aq) : balanced equation



In acidic solution

1. Write separate reduction, oxidation half-reactions.

2. For each half-reaction:

Balance elements (except H, O)

Balance O using H2O

Balance H using H+

Balance charge using electrons

3. If necessary, multiply one or both the half-reactions

by an integer to equalize number of electrons

transferred.

4. Add half-reactions.

5. Check that elements and charges are balanced.

Ex) Balance the following equation for the redox rxn occuring

in acid solution.

MnO4-(aq) + Fe2+(aq) → Fe3+(aq) + Mn2+(aq)

+7 -2 +2 +3 2+

ox re

Fe2+ → Fe3+

1. MnO4- → Mn2+

2. MnO4- → Mn2+ + 4H2O

MnO4- + 8H+ → Mn2+ + 4H2O

MnO4- + 8H+ + 5e- → Mn2+ + 4H2O

Fe2+ → Fe3+ + e-

3. MnO4- + 8H+ + 5e- → Mn2+ + 4H2O

5Fe2+ → 5Fe3+ + 5e-

4. MnO4- + 5Fe2+ + 8H+ →

Mn2+ + 5Fe3+ + 4H2O

5. Check charge and mass.



In basic solution

1. Write separate reduction, oxidation half-reactions.

2. For each half-reaction:

Balance elements (except H, O)

Balance O using H2O

Balance H using H+

Balance charge using electrons

3. Add OH- that equals H+ ions (both sides!)

4. If necessary, multiply one or both the half-reactions

by an integer to equalize number of electrons

transferred.

5. Add half-reactions.

6. Check that elements and charges are balanced.

Ex) Balance the following equation for the redox rxn occuring

in basic solution.

Ag(s) + CN-(aq) + O2(g) → Ag(CN)2-(aq)

O2 →

1. Ag + CN- → Ag(CN)2-

6. Check charge and mass.0 -1(CN-) 0 +1 -1(CN-)

oxidation reduction

2. Ag + 2CN- → Ag(CN)2-

Ag + 2CN- → Ag(CN)2- + e-

O2 → 2H2O

O2 + 4H+ → 2H2O

O2 + 4H+ + 4e- → 2H2O

3. Ag + 2CN- → Ag(CN)2- + e-

O2 + 4H+ + 4OH- + 4e- → 2H2O + 4OH-

O2 + 4H2O + 4e- → 2H2O + 4OH-

O2 + 2H2O + 4e- → 4OH-

4. 4Ag + 8CN- → 4Ag(CN)2- + 4e-

O2 + 2H2O + 4e- → 4OH-

5. 4Ag + 8CN- + O2 + 2H2O →

4Ag(CN)2- + 4OH-

chapter 4: types of chemical reactions and solution...

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