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REACTIONS IN AQUEOUS SOLUTIONS:

Predicting whether a reaction will occurReactions with a solid productDescribing reactions in aqueous solutionsReactions that form water: Acids and BasesReactions of metals with non-metals (Oxidation-Reduction Reactions)Classification of reactionsOther classifications

Homework Problems:7.1: 2 7.2: 3, 4, 9, 10, 11, 13, 21, 227.3: 25, 267.4: 397.5: 507.6: 547.7: 61, 64, 66


Predicting whether a reaction will occur

JUST BECAUSE A REACTION IS POSSIBLE DOES NOT NECESSARILY MEAN IT WILL OCCUR.

THERE ARE TWO ISSUES: 1. WHETHER A REACTION “WANTS TO OCCUR”

Paper + oxygen carbon dioxide + water

Reactants Products

2. WHETHER SUFFICIENT ENERGY IS PRESENT TO START THE PROCESS

SOME POTENTIAL DRIVING FORCES*Formation of a solid*Formation of (removable) water*Transfer of electrons*Formation of a gas

REACTIONS IN AQUEOUS SOLUTIONS:Reaction is which a solid forms

One driving force is formation of a solid:PRECIPITATION

Precipitate

CHEMICAL CHANGE OCCURRED.WHAT CHEMICAL REACTION FORMULA DESCRIBES

WHAT HAPPENED

Break the problem up:Reactant entities known.What happens when these dissolve in water?What possible products could form?Can we guess what the precipitate might be?Are there rules to guide us on what precipitates?

KCl (aq) + AgNO3 (aq)Colorless Colorless

REACTIONS IN AQUEOUS SOLUTIONS:Reactants dissolving in water

The starting solids are ionic compounds.

They are neutral.

When dissolved in water, they separate and the individual ions move around separately.

This can be demonstrated through in creased conductivity of water that they are dissolved in.

STRONG ELECTROLYTE: Substance which when dissolved in water increases conductance of water.


ADDITIONAL EXAMPLES INAQUEOUS SOLUTIONS:Reactants dissolving in water


K+

K+ K+

K+

Cl-

Cl-

Ag+ NO3-

NO3-

Ions separate.Ratios of ions determined by original compound

K+ (aq)+ Cl- (aq)+Ag+(aq)+NO3-(aq)

Ag+

Cl-

Cl-


How to decide what products form

K+

Cl-

Ag+

NO3-

KNO3 KCl

Ag NO3 AgCl

Likely precipitate

Like charged ions don’t combineStarting solutions do not precipitateProducts have net charge of zeroThink of possible verification experiments


K+ (aq)+ Cl- (aq)+Ag+(aq)+NO3-(aq)


Final Description

AgCl (s) + KNO3 (aq) White Colorless

K+

K+NO3

-

NO3-

AgClAgCl


REACTIONS IN AQUEOUS SOLUTIONS:Reaction is which a solid forms

One driving force is formation of a solid:PRECIPITATION

Yellow Precipitate

CHEMICAL CHANGE OCCURRED.WHAT CHEMICAL REACTION FORMULA DESCRIBES

WHAT HAPPENED

Break the problem up:Reactant entities known.What happens when these dissolve in water?What possible products could form?Can we guess what the precipitate might be?Are there rules to guide us on what precipitates?

K2CrO4(aq) + Ba(NO3 )2 (aq)Yellow Colorless

REACTIONS IN AQUEOUS SOLUTIONS:Reactants dissolving in water

The starting solids are ionic compounds.

They are neutral.

When dissolved in water, they separate and the individual ions move around separately.

This can be demonstrated through in creased conductivity of water that they are dissolved in.

STRONG ELECTROLYTE: Substance which when dissolved in water increases conductance of water.

K2CrO4(aq) + Ba(NO3 )2 (aq) Yellow Colorless


K+

K+ K+

K+

CrO42- Ba2+ NO3

-


2K+ (aq)+ CrO42-(aq)+Ba2+(aq)+2NO3

-(aq)


CrO42-

Ba2+

NO3-

NO3-

NO3-



K+

CrO42-

Ba2+

NO3-

KNO3 K2CrO4

BaNO3 BaCrO4

Likely precipitate




-(aq)


Final Description

BaCrO4(s) + 2KNO3 (aq) Yellow Colorless

K+

K+NO3

-

NO3-

BaCrO4


DESCRIBING REACTIONS IN AQUEOUS SOLUTIONS:

Observation:

Molecular Equation:

Complete Ionic Equation:

Net Ionic Equation:


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

-(aq)

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

Ba2+(aq) + CrO42-(aq) BaCrO4(s)


Yellow Precipitate

SPECTATOR IONS


Na+

Na+ Na+

Na+

SO42- Pb2+ NO3

-


2Na+ (aq)+ SO42-(aq)+Pb2+(aq)+2NO3

-(aq)

Na2SO4(aq) + Pb(NO3 )2 (aq)

SO42-

Pb2+

NO3-

NO3-

NO3-



Na+

SO42-

Pb2+

NO3-

NaNO3 Na2SO4

PbNO3 PbSO4

Likely precipitate




-(aq)


Final Description

PbSO4(s) + 2NaNO3 (aq) Precipitate Colorless

Na+

Na+NO3

-

NO3-

PbSO4


DESCRIBING REACTIONS IN AQUEOUS SOLUTIONS:

Observation:

Molecular Equation:


Net Ionic Equation:


-(aq)PbSO4(s) + 2Na+ (aq)+ 2NO3

-(aq)

Na2SO4(aq) + Pb(NO3 )2 (aq)PbSO4(s) + 2NaNO3 (aq)

Pb2+(aq) + SO42-(aq) PbSO4(s)


Precipitate

SPECTATOR IONS

REACTIONS THAT FORM WATER:ACIDS AND BASES

TWO VERY IMPORTANT CLASSES OF COMPOUNDS.

Mineral acids known as far back as the 1300In late 1800s, Arrhenius proposed that….

An acid is a substance that produces H+ ions (protons) when it is dissolved in water.

Strong acids dissociate completely into protons and the counter anion (Stong electrolytes).

HCl (g) H+ (aq) + Cl-(aq)

HNO3 H+ (aq)+ NO3-(aq)

H2SO4 H+ (aq)+ HSO4-(aq)

REACTIONS THAT FORM WATER:ACIDS AND BASES

TWO VERY IMPORTANT CLASSES OF COMPOUNDS.

A Base is a substance that produces OH- ions (hydroxide ions) when it is dissolved in water.

Strong bases dissociate completely into hydroxide ions and the counter cation.

NaOH (s) Na+ (aq) + OH-(aq)

KOH (s) K+ (aq)+ OH-(aq)

ACIDS and BASES

Dissolved in water

H+

H+ H+

H+

Cl- Na+


HCl (aq) + NaOH (aq)

Cl-OH-

Cl-

Cl-

OH-

OH-

OH-

Na+

Na+

Na+

ACID-BASE REACTIONS IN AQUEOUS SOLUTIONS:

H+

Cl-

Na+

OH-

H2O HCl

NaOH NaCl

Like charged ions don’t combineStarting solutions do not precipitateProducts have net charge of zero

HCl (aq) + NaOH (aq)Colorless Colorless

H+ (aq)+ OH- (aq)+Na+(aq)+Cl-(aq)

DESCRIBING REACTIONSBETWEEN ACIDS AND BASES

Observation:

Molecular Equation:


Net Ionic Equation:

H+ (aq) + Cl-(aq) + Na+(aq) + OH-(aq)H2O (l) + Na+ (aq) + Cl-(aq)

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

H+ (aq) + OH-(aq) H2O (l)

Note salt formation!

HCl (aq) + NaOH (aq) Colorless Colorless

Colorless

SPECTATOR IONS

DESCRIBING REACTIONSBETWEEN ACIDS AND BASES

Observation:

Molecular Equation:


Net Ionic Equation:

H+ (aq) + NO3-(aq) + K+(aq) + OH-(aq)

H2O (l) + K+ (aq) + NO3-(aq)

HNO3 (aq) + KOH(aq)KNO3 (aq) + H2O (l)

H+ (aq) + OH-(aq) H2O (l)

HNO3 (aq) + KOH (aq) Colorless Colorless

Colorless

SPECTATOR IONS

Note salt formation!

REACTIONS OF METALS WITH NON-METALS

(OXIDATION-REDUCTION REACTIONS):TO LEARN GENERAL CHARACTERISTICS OF A REACTION

BETWEEN A METAL AND A NON-METAL

TO RECOGNIZE ELECTRON TRANSFER AS A DRIVING FORCE FOR A CHEMICAL REACTION

23

Na11

23

Na+

11

11-

NeutralSodiumAtom

11+ 11+

10-

SodiumIon

IONIZATION OF SODIUM

Na Na+ + e-

9-

9+ 9+

10-

FluorineAtom

FluorideIon

19

F9

19

F-

9

IONIZATION OF FLUORINE

F + e- F-

11-

11+

SodiumAtom

9-

9+

Fluorine Atom

e-

10-

11+

SodiumIon(+)

10-

9+

Fluorine Ion(-)

AN OXIDATION-REDUCTION REACTION

2Na + F2 2 NaF

+

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

Mg Mg 2+ + 2e-

O + 2e- O 2-

Examples of Oxidation-Reduction Reactions

Mg

Mg

O

O

2e-

2e-

Mg 2+

Mg 2+

O 2-

O 2-

2Al(s) + Fe2O3(s) 2Fe(s) + Al2O3(s)


Al Al 3+ + 3e-

Fe 3+

+ 3e- Fe

Al

Al

O O

Al 3+

Al 3+

O

Fe 3+

Fe 3+

O O O

Fe

Fe3e-

3e-

2Al(s) + 3I2(s) 2Al I3(s)


Al Al 3+ + 3e-

I + e- I-

Al

Al

I IAl 3+

Al 3+

I I

I I

I -

I -

I -

I -

I -

I -

CLASSIFICATION SCHEMES FOR REACTIONS:

One Approach

FORMATION OF A SOLID

FORMATION OF WATER

TRANSFER OF ELECTRONS

K2CrO4 + Ba(NO3 )2 BaCrO4 + 2KNO3

Solution Solution Solid Solution

Precipitation ReactionDouble displacement Reaction

HCl + NaOH NaCl + H2O

Solution Solution Solution Liquid

Acid-Base Reaction

2Na + F2 2 NaF

Solid Gas Solid

Oxidation-Reduction Reaction

FORMATION OF A GAS

2HCl + Na 2CO3 CO2 + H2O + NaCl

Solution Solution Gas Liquid Solution

CLASSIFICATION SCHEMES FOR REACTIONS:

Another Approach

COMBUSTION REACTIONS

SYNTHESIS (COMBINATION) REACTIONS

DECOMPOSITION REACTIONS

C3H8 + 5 O2 3 CO2 + 4H2OPropane Gas Gas Gas Gas

C8H18 + 25 O2 16 CO2 + 18 H2OGasoline liquid Gas Gas Gas

C + O2 CO2

Coal solid Gas Gas

2H2 + O2 H2O C + O2 CO2

N2 + O2 2NO

2H2O 2H2 + O2 2HgO 2Hg + O2 2NaCl 2Na + Cl2

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