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MIDTERM POST LABORATORY DISCUSSION. Adapted from ppt created by Andrea D. Leonard University of Louisiana at Lafayette. POLARITY. Properties of Organic Compounds Polarity. A covalent bond is nonpolar when two atoms of identical or similar electronegativity are bonded.

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Midterm post laboratory discussion

MIDTERM POST LABORATORY DISCUSSION

Adapted from ppt created by

Andrea D. Leonard

University of Louisiana at Lafayette


Polarity

POLARITY


Properties of organic compounds polarity

Properties of Organic CompoundsPolarity

  • A covalent bond is nonpolar when two atoms of

  • identical or similar electronegativity are bonded.

  • Thus, C–C and C–H bonds are nonpolar bonds.

  • A covalent bond is polar when atoms of different

  • electronegativity are bonded.

  • Thus, bonds between carbon and N, O, and the

  • halogens are polar bonds.


Properties of organic compounds polarity1

Properties of Organic CompoundsPolarity

  • If a single bond is polar,

  • the molecule is polar because it contains a net dipole.

  • Hydrocarbons contain

  • only nonpolar C–C and

  • C–H bonds, so they are

  • nonpolar molecules.


Properties of organic compounds polarity2

Properties of Organic CompoundsPolarity

  • If the individual polar

  • bonds (dipoles) cancel

  • in a molecule, the

  • molecule is nonpolar.

  • If the individual bond

  • dipolesdo not cancel, the

  • molecule is polar.


Intermolecular forces

INTERMOLECULAR FORCES


Intermolecular forces1

Intermolecular Forces


Boiling point and melting point

BOILING POINT AND MELTING POINT


Intermolecular forces boiling point and melting point

Intermolecular ForcesBoiling Point and Melting Point

  • The boiling point is the temperature at which a

  • liquid is converted to the gas phase.

  • The melting point is the temperature at which a

  • solid is converted to the liquid phase.

  • The stronger the intermolecular forces, the higher

  • the boiling point and melting point.


Intermolecular forces boiling point and melting point1

Intermolecular ForcesBoiling Point and Melting Point


Intermolecular forces boiling point and melting point2

Intermolecular ForcesBoiling Point and Melting Point

  • Both propane and butane have London

  • dispersion forces and nonpolar bonds.

  • In this case, the larger molecule will have stronger

  • attractive forces.


The liquid state vapor pressure

The Liquid StateVapor Pressure

  • Evaporation is the conversion of liquids into the

  • gas phase.

  • Evaporation is endothermic—it absorbs heat from

  • the surroundings.

  • Condensation is the conversion of gases into the

  • liquid phase.

  • Condensation is exothermic—it gives off heat to

  • the surroundings.


The liquid state vapor pressure1

The Liquid StateVapor Pressure

  • Vapor pressure is the pressure exerted by gas

  • molecules in equilibrium with the liquid phase.

  • Vapor pressure increases with increasing

  • temperature.


The liquid state vapor pressure2

The Liquid StateVapor Pressure

  • The stronger the intermolecular forces, the lower

  • the vapor pressure at a given temperature.


The liquid state viscosity and surface tension

The Liquid StateViscosity and Surface Tension

Viscosity is a measure of a fluid’s resistance to flow

freely.

  • A viscous liquid feels “thick.”

  • Compounds with strong intermolecular forces

  • tend to be more viscous than compounds with weaker forces.

  • Substances composed of large molecules tend to be more viscous, too, because large molecules do not slide past each other as freely.


The liquid state viscosity and surface tension1

The Liquid StateViscosity and Surface Tension

Surface tension is a measure of the resistance of a

liquid to spread out.

  • Interior molecules in a

  • liquid are surrounded by

  • intermolecular forces on

  • all sides.

  • Surface molecules only

  • experience intermolecular

  • forces from the sides and

  • from below.


The liquid state viscosity and surface tension2

The Liquid StateViscosity and Surface Tension

  • The stronger the intermolecular forces, the stronger

  • the surface molecules are pulled down toward the

  • interior of a liquid and the higher the surface tension.

  • Water has a very high surface tension because

  • of its strong intermolecular hydrogen bonding.

  • Small objects can seem to “float” on the surface

  • of water.

  • These normally heavy objects and are held up by

  • the surface tension only.


The solid state types of solids

The Solid StateTypes of Solids

  • Solids can be either crystalline or amorphous.

  • A crystalline solid has a regular arrangement of

  • particles—atoms, molecules, or ions—with a repeating structure.

  • An amorphous solid has no regular arrangement of its closely packed particles.

  • There are four different types of crystalline solids—ionic, molecular, network, and metallic.


The solid state crystalline solids

The Solid StateCrystalline Solids

  • An ionic solid is composed

  • of oppositely charged ions

  • (NaCl).

  • A molecular solid is

  • composed of individual

  • molecules arranged

  • regularly (H2O).


The solid state crystalline solids1

The Solid StateCrystalline Solids

  • A network solid is composed

  • of a vast number of atoms

  • covalently bonded together

  • (SiO2).

  • A metallic solid is a lattice

  • of metal cations

  • surrounded by a cloud of

  • e− that move freely (Cu).


The solid state amorphous solids

The Solid StateAmorphous Solids

Amorphous solids have no regular arrangement of

their particles.

  • They can be formed when liquids cool too quickly

  • for regular crystal formation.

  • Very large covalent molecules tend to form

  • amorphous solids, because they can become folded and intertwined.

  • Examples include rubber, glass, and plastic.


Energy and phase changes converting a solid to a liquid

Energy and Phase ChangesConverting a Solid to a Liquid

liquid water

solid water

The amount of energy needed to melt 1 gram of a

substance is called its heat of fusion.


Energy and phase changes converting a liquid to a gas

Energy and Phase ChangesConverting a Liquid to a Gas

gaseous water

liquid water

The amount of energy needed to vaporize 1 gram of

a substance is called its heat of vaporization.


Energy and phase changes converting a solid to a gas

Energy and Phase ChangesConverting a Solid to a Gas

gaseous CO2

solid CO2


Solubility

SOLUBILITY


Solutions introduction

SolutionsIntroduction

A solution is a homogeneous mixture that contains

small particles. Liquid solutions are transparent.

A colloid is a homogeneous mixture with larger

particles, often having an opaque appearance.

Solutions consist of two parts:

  • The solute is the substance present in a lesser amount.

  • The solvent is the substance present in a larger amount.

An aqueous solution has water as the solvent.


Solutions introduction1

SolutionsIntroduction

Three different types of solutions:

a solution of

gases (O2, CO2,

and N2)

an aqueous

solution of NaCl

(a solid in a liquid)

Hg(l) dissolved

in Ag(s)

(a liquid in a

solid)


Solutions introduction2

SolutionsIntroduction

  • A substance that conducts

  • an electric current in water

  • is called an electrolyte.

  • A substance that does

  • not conduct an electric

  • current in water is

  • called a nonelectrolyte.

NaCl(aq) dissociates into

Na+(aq) and Cl−(aq)

H2O2 does not

dissociate


Solubility general features

SolubilityGeneral Features

Solubility is the amount of solute that dissolves in a

given amount of solvent.

  • It is usually reported in grams of solute per 100 mL

  • of solution (g/100 mL).

  • A saturated solution contains the maximum

  • number of grams of solute that can dissolve.

  • An unsaturated solution contains less than the

  • maximum number of grams of solute that can dissolve.


Solubility basic principles

SolubilityBasic Principles

Solubility can be summed up as “like dissolves like.”

  • Most ionic and polar covalent compounds are

  • soluble in water, a polar solvent.


Solubility basic principles1

SolubilityBasic Principles

  • Small neutral molecules with O or N atoms that can hydrogen bond to water are water soluble.

Ethanol can hydrogen bond to water.


Solubility basic principles2

SolubilityBasic Principles

  • Nonpolar compounds are soluble in nonpolar

  • solvents (i.e., like dissolves like).

  • Octane (C8H18) dissolves in CCl4 because both are

  • nonpolar liquids that exhibit only London dispersion

  • forces.

octane + CCl4

octane

CCl4


Properties of organic compounds solubility

Properties of Organic CompoundsSolubility

  • The rule of solubility is “like dissolves like.”

  • Most organic compounds are soluble in organic

  • solvents.

  • Hydrocarbons and other nonpolar organic

  • compounds are insoluble in water.

  • Polar organic compounds are water soluble only

  • if they are small and contain a N or O atom that

  • can hydrogen bond with water.


Properties of organic compounds solubility1

Properties of Organic CompoundsSolubility

CH3CH2CH2CH2CH2CH3

hexane

CH3CH2—OH

ethanol

  • small nonpolar molecule

  • no O or N present

  • H2O insoluble

  • organic solvent soluble

  • small polar molecule

  • O atom present

  • H2O soluble

  • organic solvent soluble


Properties of organic compounds solubility2

Properties of Organic CompoundsSolubility

cholesterol

  • very large molecule

  • O atom present

  • too many nonpolar C—C and C—H bonds

  • H2O insoluble

  • organic solvent soluble


Solubility basic principles3

SolubilityBasic Principles

  • When solvation releases more energy than that

  • required to separate particles, the overall process

  • is exothermic (heat is released).

  • When the separation of particles requires more

  • energy than is released during solvation, the

  • process is endothermic (heat is absorbed).


Solubility ionic compounds additional principles

SolubilityIonic Compounds—Additional Principles

General Rules for the Solubility of Ionic Compounds

Rule[1] A compound is soluble if it contains one of

the following cations:

  • Group 1A cations: Li+, Na+, K+, Rb+, Cs+

  • Ammonium, NH4+


Solubility ionic compounds additional principles1

SolubilityIonic Compounds—Additional Principles

General Rules for the Solubility of Ionic Compounds

Rule[2] A compound is soluble if it contains one of

the following anions:

  • Halide: Cl−, Br−, I−, except for salts with

  • Ag+, Hg22+, and Pb2+

  • Nitrate, NO3−

  • Acetate, CH3CO2−

  • Sulfate, SO42−, except for salts with Ba2+,

  • Hg22+, and Pb2+


Alcohols

ALCOHOLS


Structure and properties of alcohols

Structure and Properties of Alcohols

  • An alcohol contains an O atom with a bent shape

  • like H2O, with a bond angle of 109.5o.

  • Alcohols have two polar bonds, C—O and O—H,

  • with a bent shape, therefore it has a net dipole.


Structure and properties of alcohols1

Structure and Properties of Alcohols

  • Alcohols have an H atom bonded to an O atom,

  • making them capable of intermolecular hydrogen

  • bonding.

  • All of these properties give alcohols much stronger

  • intermolecular forces than alkanes and alkenes.


Structure and properties of alcohols2

Structure and Properties of Alcohols

  • Therefore, alcohols have higher boiling and melting

  • points than hydrocarbons of comparable size and

  • shape.

stronger intermolecular forces

higher boiling and melting point


Structure and properties of alcohols3

Structure and Properties of Alcohols

  • Alcohols are soluble in organic solvents.

  • Low molecular weight alcohols (6 C’s or less)

  • are soluble in water.

  • Higher molecular weight alcohols (6 C’s or more)

  • are not soluble in water.

2 C’s in chain

water soluble

8 C’s in chain

water insoluble


Acids and bases

ACIDS AND BASES


Introduction to acids and bases

Introduction to Acids and Bases

The earliest definition was given by Arrhenius:

  • An acid contains a hydrogen atom and dissolves

  • in water to form a hydrogen ion, H+.

HCl(g)

H+(aq) + Cl−(aq)

acid

  • A base contains hydroxide and dissolves in water

  • to form −OH.

NaOH(s)

Na+(aq) + −OH(aq)

base


Introduction to acids and bases1

Introduction to Acids and Bases

  • The Arrhenius definition correctly predicts the

  • behavior of many acids and bases.

  • However, this definition is limited and sometimes

  • inaccurate.

  • For example, H+does not exist in water. Instead, it

  • reacts with water to form the hydronium ion, H3O+.

H+(aq) + H2O(l)

H3O+(aq)

hydronium ion:

actually present in

aqueous solution

hydrogen ion:

does not really exist

in solution


Introduction to acids and bases2

Introduction to Acids and Bases

The Brønsted–Lowry definition is more widely used:

  • A Brønsted–Lowry acid is a proton (H+) donor.

  • A Brønsted–Lowry base is a proton (H+) acceptor.

This proton is donated.

HCl(g) + H2O(l)

H3O+(aq) + Cl−(aq)

  • HCl is a Brønsted–Lowry acid because it donates

  • a proton to the solvent water.

  • H2O is a Brønsted–Lowry base because it accepts

  • a proton from HCl.


Introduction to acids and bases br nsted lowry acids

Introduction to Acids and BasesBrønsted–Lowry Acids

  • A Brønsted–Lowry acid must contain a hydrogen

  • atom.

  • Common Brønsted–Lowry acids (HA):

HCl

hydrochloric acid

H2SO4

sulfuric acid

H

O

HBr

hydrobromic acid

acidic H

atom

H

C

C

H

O

H

HNO3

nitric acid

acetic acid


Introduction to acids and bases br nsted lowry acids1

Introduction to Acids and BasesBrønsted–Lowry Acids

  • A monoprotic acid contains one acidic proton.

HCl

  • A diprotic acid contains two acidic protons.

H2SO4

  • A triprotic acid contains three acidic protons.

H3PO4

  • A Brønsted–Lowry acid may be neutral or it may

  • carry a net positive or negative charge.

HCl, H3O+, HSO4−


Introduction to acids and bases br nsted lowry bases

Introduction to Acids and BasesBrønsted–Lowry Bases

  • A Brønsted–Lowry base is a proton acceptor,

  • so it must be able to form a bond to a proton.

  • A base must contain a lone pair of electrons that

  • can be used to form a new bond to the proton.

This e− pair forms a new

bond to a H from H2O.

+

H

+ H2O(l)

H

N

H

H

N

H

+ −OH(aq)

H

H

Brønsted–Lowry

base


Introduction to acids and bases br nsted lowry bases1

NH3

ammonia

H2O

water

Introduction to Acids and BasesBrønsted–Lowry Bases

  • Common Brønsted–Lowry Bases (B )

Lone pairs make these

neutral compounds bases.

The −OH is the base in

each metal salt.

NaOH

sodium hydroxide

KOH

potassium hydroxide

Mg(OH)2

magnesium hydroxide

Ca(OH)2

calcium hydroxide


Proton transfer the reaction of a br nsted lowry acid with a br nsted lowry base

A−

B

Proton TransferThe Reaction of a Brønsted–Lowry Acid witha Brønsted–Lowry Base

This e− pair forms

a new bond to H+.

This e− pair

stays on A.

gain of H+

H

A

+

+

H

B+

acid

base

loss of H+


Proton transfer the reaction of a br nsted lowry acid with a br nsted lowry base1

A−

B

Proton TransferThe Reaction of a Brønsted–Lowry Acid witha Brønsted–Lowry Base

gain of H+

H

A

+

+

H

B+

conjugate

acid

acid

base

conjugate

base

loss of H+

  • The product formed by loss of a proton from an

  • acid is called its conjugate base.

  • The product formed by gain of a proton by a base

  • is called its conjugate acid.


Proton transfer the reaction of a br nsted lowry acid with a br nsted lowry base2

Proton TransferThe Reaction of a Brønsted–Lowry Acid witha Brønsted–Lowry Base

gain of H+

H2O

H

Br

+

Br−

H3O+

+

conjugate

acid

acid

base

conjugate

base

loss of H+

  • HBr and Br− are a conjugate acid–base pair.

  • H2O and H3O+ are a conjugate acid–base pair.

  • The net charge must be the same on both sides

  • of the equation.


Proton transfer the reaction of a br nsted lowry acid with a br nsted lowry base3

Proton TransferThe Reaction of a Brønsted–Lowry Acid witha Brønsted–Lowry Base

  • When a species gains a proton (H+), it gains a +1

  • charge.

add H+

H2O

base

zero charge

H3O+

+1 charge

  • When a species loses a proton (H+), it effectively

  • gains a −1 charge.

lose H+

HBr

acid

zero charge

Br−

−1 charge


Proton transfer the reaction of a br nsted lowry acid with a br nsted lowry base4

Proton TransferThe Reaction of a Brønsted–Lowry Acid witha Brønsted–Lowry Base

Amphoteric compound: A compound that contains

both a hydrogen atom and a lone pair of e−; it can

be either an acid or a base.

+

H

add H+

H

O

H

H

O

H

H2O as a base

conjugate acid

remove H+

H

O

H

H

O

H2O as an acid

conjugate base


Introduction to acids and bases3

Introduction to Acids and Bases

The earliest definition was given by Arrhenius:

  • An acid contains a hydrogen atom and dissolves

  • in water to form a hydrogen ion, H+.

HCl(g)

H+(aq) + Cl−(aq)

acid

  • A base contains hydroxide and dissolves in water

  • to form −OH.

NaOH(s)

Na+(aq) + −OH(aq)

base


Introduction to acids and bases4

Introduction to Acids and Bases

  • The Arrhenius definition correctly predicts the

  • behavior of many acids and bases.

  • However, this definition is limited and sometimes

  • inaccurate.

  • For example, H+does not exist in water. Instead, it

  • reacts with water to form the hydronium ion, H3O+.

H+(aq) + H2O(l)

H3O+(aq)

hydronium ion:

actually present in

aqueous solution

hydrogen ion:

does not really exist

in solution


Introduction to acids and bases5

Introduction to Acids and Bases

The Brønsted–Lowry definition is more widely used:

  • A Brønsted–Lowry acid is a proton (H+) donor.

  • A Brønsted–Lowry base is a proton (H+) acceptor.

This proton is donated.

HCl(g) + H2O(l)

H3O+(aq) + Cl−(aq)

  • HCl is a Brønsted–Lowry acid because it donates

  • a proton to the solvent water.

  • H2O is a Brønsted–Lowry base because it accepts

  • a proton from HCl.


Introduction to acids and bases br nsted lowry acids2

Introduction to Acids and BasesBrønsted–Lowry Acids

  • A Brønsted–Lowry acid must contain a hydrogen

  • atom.

  • Common Brønsted–Lowry acids (HA):

HCl

hydrochloric acid

H2SO4

sulfuric acid

H

O

HBr

hydrobromic acid

acidic H

atom

H

C

C

H

O

H

HNO3

nitric acid

acetic acid


Introduction to acids and bases br nsted lowry acids3

Introduction to Acids and BasesBrønsted–Lowry Acids

  • A monoprotic acid contains one acidic proton.

HCl

  • A diprotic acid contains two acidic protons.

H2SO4

  • A triprotic acid contains three acidic protons.

H3PO4

  • A Brønsted–Lowry acid may be neutral or it may

  • carry a net positive or negative charge.

HCl, H3O+, HSO4−


Introduction to acids and bases br nsted lowry bases2

Introduction to Acids and BasesBrønsted–Lowry Bases

  • A Brønsted–Lowry base is a proton acceptor,

  • so it must be able to form a bond to a proton.

  • A base must contain a lone pair of electrons that

  • can be used to form a new bond to the proton.

This e− pair forms a new

bond to a H from H2O.

+

H

+ H2O(l)

H

N

H

H

N

H

+ −OH(aq)

H

H

Brønsted–Lowry

base


Introduction to acids and bases br nsted lowry bases3

NH3

ammonia

H2O

water

Introduction to Acids and BasesBrønsted–Lowry Bases

  • Common Brønsted–Lowry Bases (B )

Lone pairs make these

neutral compounds bases.

The −OH is the base in

each metal salt.

NaOH

sodium hydroxide

KOH

potassium hydroxide

Mg(OH)2

magnesium hydroxide

Ca(OH)2

calcium hydroxide


Proton transfer the reaction of a br nsted lowry acid with a br nsted lowry base5

A−

B

Proton TransferThe Reaction of a Brønsted–Lowry Acid witha Brønsted–Lowry Base

This e− pair forms

a new bond to H+.

This e− pair

stays on A.

gain of H+

H

A

+

+

H

B+

acid

base

loss of H+


Proton transfer the reaction of a br nsted lowry acid with a br nsted lowry base6

A−

B

Proton TransferThe Reaction of a Brønsted–Lowry Acid witha Brønsted–Lowry Base

gain of H+

H

A

+

+

H

B+

conjugate

acid

acid

base

conjugate

base

loss of H+

  • The product formed by loss of a proton from an

  • acid is called its conjugate base.

  • The product formed by gain of a proton by a base

  • is called its conjugate acid.


Proton transfer the reaction of a br nsted lowry acid with a br nsted lowry base7

Proton TransferThe Reaction of a Brønsted–Lowry Acid witha Brønsted–Lowry Base

gain of H+

H2O

H

Br

+

Br−

H3O+

+

conjugate

acid

acid

base

conjugate

base

loss of H+

  • HBr and Br− are a conjugate acid–base pair.

  • H2O and H3O+ are a conjugate acid–base pair.

  • The net charge must be the same on both sides

  • of the equation.


Proton transfer the reaction of a br nsted lowry acid with a br nsted lowry base8

Proton TransferThe Reaction of a Brønsted–Lowry Acid witha Brønsted–Lowry Base

  • When a species gains a proton (H+), it gains a +1

  • charge.

add H+

H2O

base

zero charge

H3O+

+1 charge

  • When a species loses a proton (H+), it effectively

  • gains a −1 charge.

lose H+

HBr

acid

zero charge

Br−

−1 charge


Proton transfer the reaction of a br nsted lowry acid with a br nsted lowry base9

Proton TransferThe Reaction of a Brønsted–Lowry Acid witha Brønsted–Lowry Base

Amphoteric compound: A compound that contains

both a hydrogen atom and a lone pair of e−; it can

be either an acid or a base.

+

H

add H+

H

O

H

H

O

H

H2O as a base

conjugate acid

remove H+

H

O

H

H

O

H2O as an acid

conjugate base


Acid and base strength relating acid and base strength

Acid and Base StrengthRelating Acid and Base Strength

  • When a covalent acid dissolves in water, the proton

  • transfer that forms H3O+ is called dissociation.

  • When a strong acid dissolves in water, 100% of

  • the acid dissociates into ions.

HCl(g) + H2O(l)

H3O+(aq) + Cl−(aq)

  • A single reaction arrow is used, because the

  • product is greatly favored at equilibrium.

  • Common strong acids are HI, HBr, HCl, H2SO4,

  • and HNO3.


Acid and base strength relating acid and base strength1

Acid and Base StrengthRelating Acid and Base Strength

  • When a weak acid dissolves in water, only a

  • small fraction of the acid dissociates into ions.

  • Unequal reaction arrows are used, because the reactants are usually favored at equilibrium.

CH3COOH(l) + H2O(l)

H3O+(aq) + CH3COO−(aq)

  • Common weak acids are H3PO4, HF, H2CO3, and

  • HCN.


Acid and base strength relating acid and base strength2

Acid and Base StrengthRelating Acid and Base Strength

A weak acid contains

mostly undissociated

acid, CH3COOH.

A strong acid, HCl, is

completely dissociated

into H3O+(aq) and Cl−(aq).


Acid and base strength relating acid and base strength3

Acid and Base StrengthRelating Acid and Base Strength

  • When a strong base dissolves in water, 100% of

  • the base dissociates into ions.

NaOH(s) + H2O(l)

Na+(aq) + −OH(aq)

  • Common strong bases are NaOH and KOH.

  • When a weakbase dissolves in water, only a

  • small fraction of the base dissociates into ions.

NH3(g) + H2O(l)

NH4+(aq) + −OH(aq)


Acid and base strength relating acid and base strength4

Acid and Base StrengthRelating Acid and Base Strength

A strong base, NaOH, is

completely dissociated

into Na+(aq) and −OH(aq).

A weak base contains

mostly undissociated

base, NH3.


Acid and base strength relating acid and base strength5

Acid and Base StrengthRelating Acid and Base Strength

  • A strong acid readily donates a proton, forming

  • a weak conjugate base.

HCl

strong acid

Cl−

weak conjugate base

  • A strong base readily accepts a proton, forming

  • a weak conjugate acid.

−OH

strong base

H2O

weak conjugate acid


Acid and base strength using acid strength to predict the direction of equilibrium

A−

B

Acid and Base StrengthUsing Acid Strength to Predict the Directionof Equilibrium

  • A Brønsted–Lowry acid–base reaction represents

  • an equilibrium.

+

H

A

+

H

B+

conjugate

acid

acid

base

conjugate

base

  • The position of the equilibrium depends upon the

  • strengths of the acids and bases.

  • The stronger acid reacts with the stronger base

  • to form the weaker acid and the weaker base.


Acid and base strength predicting the direction of equilibrium

A−

B

Acid and Base StrengthPredicting the Direction of Equilibrium

  • When the stronger acid and base are the reactants

  • on the left side, the reaction readily occurs and

  • the reaction proceeds to the right.

H

A

+

+

H

B+

stronger

acid

stronger

base

weaker

base

weaker

acid

  • A larger forward arrow means that products are

  • favored.


Acid and base strength predicting the direction of equilibrium1

A−

B

Acid and Base StrengthPredicting the Direction of Equilibrium

  • If an acid–base reaction would form the stronger

  • acid and base, equilibrium favors the reactants

  • and little product forms.

H

A

+

+

H

B+

weaker

acid

weaker

base

stronger

base

stronger

acid

  • A larger reverse arrow means that reactants are

  • favored.


Acid and base strength

Acid and Base Strength

HOW TO Predict the Direction of Equilibrium in an

Acid–Base Reaction

Are the reactants or products favored in

the following acid–base reaction?

Example

gain of H+

−CN(aq)

HCN(g)

−OH(aq)

+

H2O(l)

+

conjugate

acid

acid

base

conjugate

base

loss of H+

Identify the acid in the reactants and the

conjugate acid in the products.

Step [1]


Acid and base strength1

Acid and Base Strength

HOW TO Predict the Direction of Equilibrium in an

Acid–Base Reaction

Determine the relative strength of the acid

and the conjugate acid.

Step [2]

  • From Table 9.1, HCN is a stronger acid than H2O.

Equilibrium favors the formation of the

weaker acid.

Step [3]

−CN(aq)

HCN(g)

−OH(aq)

+

H2O(l)

+

stronger

acid

weaker

acid

Products are favored.


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