arrhenius definition

Arrhenius DefinitionArrhenius Definition

Acids produce hydrogen ions in Acids produce hydrogen ions in aqueous solution.aqueous solution.

Bases produce hydroxide ions when Bases produce hydroxide ions when dissolved in water.dissolved in water.

Limits to aqueous solutions.Limits to aqueous solutions.Only one kind of base.Only one kind of base.NHNH33 ammonia could not be an ammonia could not be an

Arrhenius base.Arrhenius base.

Bronsted-Lowry DefinitionsBronsted-Lowry Definitions

An acid is an proton (HAn acid is an proton (H++) donor and a ) donor and a base is a proton acceptor.base is a proton acceptor.

Acids and bases always come in Acids and bases always come in pairs.pairs.

HCl is an acid..HCl is an acid..When it dissolves in water it gives its When it dissolves in water it gives its

proton to water.proton to water.HCl(g) + HHCl(g) + H22O(l) O(l) HH33OO++ + Cl + Cl--

Water is a base makes hydronium ionWater is a base makes hydronium ion

PairsPairs

General equation General equation HA(aq) + HHA(aq) + H22O(l) O(l) H H33OO++(aq) + A(aq) + A--(aq)(aq) Acid + Base Acid + Base Conjugate acid +Conjugate acid +

Conjugate base Conjugate base This is an equilibrium.This is an equilibrium. CompetitionCompetition forfor H H++ betweenbetween H H22O and AO and A--

The stronger base controls direction.The stronger base controls direction. If HIf H22O is a stronger base it takes the HO is a stronger base it takes the H++ Equilibrium moves to right.Equilibrium moves to right.

Acid dissociation constant Acid dissociation constant

KKaaThe equilibrium constant for the The equilibrium constant for the general equation.general equation.

HA(aq) + HHA(aq) + H22O(l) O(l) H H33OO++(aq) + A(aq) + A--(aq)(aq)

KKaa = [H = [H33OO++][A][A--]]

[HA][HA]HH33OO++ is often written H is often written H++ ignoring the ignoring the

water in equation (it is implied).water in equation (it is implied).

Acid dissociation constant Acid dissociation constant

KKaaHA(aq) HA(aq) HH++(aq) + A(aq) + A--(aq)(aq)

KKaa = [H = [H++][A][A--]]

[HA][HA]We can write the expression for any We can write the expression for any

acid.acid.Strong acids dissociate completely.Strong acids dissociate completely.Equilibrium far to right.Equilibrium far to right.Conjugate base must be weak. Conjugate base must be weak.

Back to PairsBack to Pairs

Strong acidsStrong acids

KKaa is largeis large

[H[H++] is equal to [HA]] is equal to [HA]AA-- is a weaker base is a weaker base

than waterthan water

Weak acidsWeak acids

KKaa is smallis small

[H[H++] <<< [HA]] <<< [HA]AA-- is a stronger is a stronger

base than waterbase than water

Types of AcidsTypes of Acids

Polyprotic Acids- more than 1 acidic Polyprotic Acids- more than 1 acidic hydrogen (diprotic, triprotic).hydrogen (diprotic, triprotic).

Oxyacids - Proton is attached to the Oxyacids - Proton is attached to the oxygen of an ion.oxygen of an ion.

Organic acids contain the Carboxyl Organic acids contain the Carboxyl group -COOH with the H attached to group -COOH with the H attached to OO

Generally very weak.Generally very weak.

AmphotericAmphoteric Behave as both an acid and a base.Behave as both an acid and a base. Water autoionizesWater autoionizes 2H2H22O(l) O(l) H H33OO++(aq) + OH(aq) + OH--(aq)(aq) KKWW= [H= [H33OO++][OH][OH--]=[H]=[H++][OH][OH--]] At 25ºC KAt 25ºC KWW = 1.0 x10 = 1.0 x10-14-14 In In EVERYEVERY aqueous solution. aqueous solution. Neutral solution [HNeutral solution [H++] = [OH] = [OH--]= 1.0 x10]= 1.0 x10-7-7 Acidic solution [HAcidic solution [H++] > [OH] > [OH--]] Basic solution [HBasic solution [H++] < [OH] < [OH--]]

pHpH

pH= -log[HpH= -log[H++]]Used because [HUsed because [H++] is usually very small] is usually very smallAs pH decreases, [HAs pH decreases, [H++] increases ] increases

exponentiallyexponentiallySig figs only the digits after the decimal Sig figs only the digits after the decimal

place of a pH are significantplace of a pH are significant [H[H++] = 1.0 x 10] = 1.0 x 10-8-8 pH= 8.00 2 sig figs pH= 8.00 2 sig figspOH= -log[OHpOH= -log[OH--]]pKa = -log KpKa = -log K

RelationshipsRelationships

KKWW = [H = [H++][OH][OH--]] -log K-log KWW = -log([H = -log([H++][OH][OH--])]) -log K-log KWW = -log[H = -log[H++]+ -log[OH]+ -log[OH--]]pKpKWW = pH + pOH = pH + pOHKKWW = 1.0 x10 = 1.0 x10-14-14

14.00 = pH + pOH14.00 = pH + pOH [H[H++],[OH],[OH--],pH and pOH],pH and pOH Given Given

any one of these we can find the other any one of these we can find the other three.three.

Basic

Acidic Neutral

100

10-

1

10-

3

10-

5

10-

7

10-

9

10-

11

10-

13

10-

14

[H+]

0 1 3 5 7 9 11

13

14

pH

Basic

100

10-

1

10-

3

10-

5

10-

7

10-

9

10-

11

10-

13

10-

14

[OH-]

01357911

13

14

pOH

Calculating pH of SolutionsCalculating pH of Solutions

Always write down the major ions in Always write down the major ions in solution.solution.

Remember these are equilibria.Remember these are equilibria.Remember the chemistry.Remember the chemistry.Don’t try to memorize there is no one Don’t try to memorize there is no one

way to do this.way to do this.

Strong AcidsStrong Acids

HBr, HI, HCl, HNOHBr, HI, HCl, HNO33, H, H22SOSO44, HClO, HClO44

ALWAYS WRITE THE MAJOR SPECIESALWAYS WRITE THE MAJOR SPECIES Completely dissociatedCompletely dissociated [H[H++] = [HA]] = [HA] [OH[OH--] is going to be small because of ] is going to be small because of

equilibriumequilibrium 1010-14-14 = [H = [H++][OH][OH--]] If [HA]< 10If [HA]< 10-7-7 water contributes H water contributes H++

Weak AcidsWeak Acids

Ka will be small.Ka will be small.ALWAYS WRITE THE MAJOR SPECIES.ALWAYS WRITE THE MAJOR SPECIES. It will be an equilibrium problem from It will be an equilibrium problem from

the start.the start.Determine whether most of the HDetermine whether most of the H++

will come from the acid or the water.will come from the acid or the water.Compare Ka or KwCompare Ka or KwRest is just like last chapter.Rest is just like last chapter.

ExampleExample

Calculate the pH of 2.0 M acetic acid Calculate the pH of 2.0 M acetic acid

HCHC22HH33OO22 with a Ka 1.8 x10 with a Ka 1.8 x10-5-5

Calculate pOH, [OHCalculate pOH, [OH--], [H], [H++]]

A mixture of Weak AcidsA mixture of Weak Acids

The process is the same.The process is the same.Determine the major species.Determine the major species.The stronger will predominate.The stronger will predominate.Bigger Ka if concentrations are Bigger Ka if concentrations are

comparablecomparableCalculate the pH of a mixture 1.20 M Calculate the pH of a mixture 1.20 M

HF (Ka = 7.2 x 10HF (Ka = 7.2 x 10-4-4) and 3.4 M ) and 3.4 M

HOCHOC66HH55 (Ka = 1.6 x 10 (Ka = 1.6 x 10-10-10) )

Percent dissociationPercent dissociation

= = amount dissociated amount dissociated x 100 x 100 initial concentration initial concentration

For a weak acid percent dissociation For a weak acid percent dissociation increases as acid becomes more dilute.increases as acid becomes more dilute.

Calculate the % dissociation of 1.00 M Calculate the % dissociation of 1.00 M and .00100 M Acetic acidand .00100 M Acetic acid (Ka = 1.8 x 10 (Ka = 1.8 x 10-5-5

As [HA]As [HA]00 decreases [H decreases [H++] decreases but % ] decreases but %

dissociation increases.dissociation increases.Le ChatelierLe Chatelier

The other wayThe other way

What is the Ka of a weak acid that is What is the Ka of a weak acid that is 8.1 % dissociated as 0.100 M 8.1 % dissociated as 0.100 M solution? solution?

BasesBases

The OHThe OH-- is a strong base. is a strong base.

Hydroxides of the alkali metals are strong Hydroxides of the alkali metals are strong bases because they dissociate completely bases because they dissociate completely when dissolved.when dissolved.

The hydroxides of alkaline earths Ca(OH)The hydroxides of alkaline earths Ca(OH)22

etc. are strong dibasic bases, but they etc. are strong dibasic bases, but they don’t dissolve well in water.don’t dissolve well in water.

Used as antacids because [OHUsed as antacids because [OH-- ] can’t ] can’t

build up.build up.

Bases without OHBases without OH--

Bases are proton acceptors.Bases are proton acceptors.

NHNH33 + H + H22O O NHNH44++ + OH + OH--

It is the lone pair on nitrogen that It is the lone pair on nitrogen that accepts the proton.accepts the proton.

Many weak bases contain NMany weak bases contain N BB(aq) (aq) + H+ H22O(l)O(l) BH BH++(aq) (aq) + OH+ OH- - (aq)(aq)

KKbb = [ = [BHBH++][][OHOH- - ]]

[ [BB] ]

Strength of BasesStrength of Bases

N:

Hydroxides are strong.Hydroxides are strong.Others are weak.Others are weak.Smaller Smaller KKbb weaker base. weaker base.

Calculate the pH of a solution of 4.0 Calculate the pH of a solution of 4.0 M pyridineM pyridine (Kb = 1.7 x 10(Kb = 1.7 x 10-9-9))

Polyprotic acidsPolyprotic acids

Always dissociate stepwise.Always dissociate stepwise.The first HThe first H++ comes of much easier comes of much easier

than the second.than the second.Ka for the first step is much bigger Ka for the first step is much bigger

than Ka for the second.than Ka for the second.Denoted KaDenoted Ka11, Ka, Ka22, Ka, Ka33

Polyprotic acidPolyprotic acid

HH22COCO33 HH++ + HCO + HCO33--

KaKa11= 4.3 x 10= 4.3 x 10-7-7

HCOHCO33-- HH++ + CO + CO33

-2-2

KaKa22= 4.3 x 10= 4.3 x 10-10-10

Base in first step is acid in second.Base in first step is acid in second. In calculations we can normally In calculations we can normally

ignore the second dissociation.ignore the second dissociation.

Calculate the ConcentrationCalculate the Concentration

Of all the ions in a solution of 1.00 M Of all the ions in a solution of 1.00 M Arsenic acid HArsenic acid H33AsOAsO44

KaKa11 = 5.0 x 10 = 5.0 x 10-3-3

KaKa22 = 8.0 x 10 = 8.0 x 10-8-8

KaKa33 = 6.0 x 10 = 6.0 x 10-10-10

Sulfuric acid is specialSulfuric acid is special

In first step it is a strong acid.In first step it is a strong acid.KaKa22 = 1.2 x 10 = 1.2 x 10-2-2

Calculate the concentrations in a 2.0 Calculate the concentrations in a 2.0 M solution of HM solution of H22SOSO44

Calculate the concentrations in a 2.0 Calculate the concentrations in a 2.0 x 10x 10-3-3 M solution of H M solution of H22SOSO44

Salts as acids an basesSalts as acids an bases

Salts are ionic compounds.Salts are ionic compounds.Salts of the cation of strong bases Salts of the cation of strong bases

and the anion of strong acids are and the anion of strong acids are neutral.neutral.

for example NaCl, KNOfor example NaCl, KNO33

There is no equilibrium for strong There is no equilibrium for strong acids and bases.acids and bases.

We ignore the reverse reaction.We ignore the reverse reaction.

Basic SaltsBasic Salts

If the anion of a salt is the conjugate base If the anion of a salt is the conjugate base of a weak acid - basic solution.of a weak acid - basic solution.

In an aqueous solution of NaFIn an aqueous solution of NaF The major species are NaThe major species are Na++, F, F--, and H, and H22OO FF- - + H+ H22O O HF + OHHF + OH--

KKbb =[HF][OH=[HF][OH--]] [F[F- - ]]

but Ka = [Hbut Ka = [H++][F][F--]] [HF] [HF]


KKaa x K x Kb b = [HF][OH= [HF][OH--]] x [Hx [H++][F][F--]]

[F[F- - ] ] [HF] [HF]



[F[F- - ] ] [HF] [HF]KKaa x K x Kb b =[OH=[OH--] [H] [H++]]



[F[F- - ] ] [HF] [HF]KKaa x K x Kb b =[OH=[OH--] [H] [H++]]

KKaa x K x Kb b = K= KWW

KKaa tells us K tells us Kbb

The anion of a weak acid is a weak The anion of a weak acid is a weak base.base.

Calculate the pH of a solution of 1.00 Calculate the pH of a solution of 1.00 M NaCN. Ka of HCN is 6.2 x 10M NaCN. Ka of HCN is 6.2 x 10-10-10

The CNThe CN-- ion competes with OH ion competes with OH-- for for the Hthe H+ +

Acidic saltsAcidic salts A salt with the cation of a weak base and A salt with the cation of a weak base and

the anion of a strong acid will be basic.the anion of a strong acid will be basic. The same development as bases leads The same development as bases leads

to to KKaa x K x Kb b = K= KWW

Calculate the pH of a solution of 0.40 M Calculate the pH of a solution of 0.40 M NHNH44Cl (the KCl (the Kbb of NH of NH33 1.8 x 10 1.8 x 10-5-5).).

Other acidic salts are those of highly Other acidic salts are those of highly charged metal ions.charged metal ions.

More on this later.More on this later.

Anion of weak acid, cation Anion of weak acid, cation of weak baseof weak base

KKaa > K > Kb b acidicacidic

KKaa < K < Kb b basicbasic

KKaa = K = Kb b NeutralNeutral

Structure and Acid base Structure and Acid base PropertiesProperties

Any molecule with an H in it is a Any molecule with an H in it is a potential acid.potential acid.

The stronger the X-H bond the less The stronger the X-H bond the less acidic (compare bond dissociation acidic (compare bond dissociation energies).energies).

The more polar the X-H bond the The more polar the X-H bond the stronger the acid (use stronger the acid (use electronegativities).electronegativities).

The more polar H-O-X bond -The more polar H-O-X bond -stronger acid.stronger acid.

Strength of oxyacidsStrength of oxyacids

The more oxygen hooked to the The more oxygen hooked to the central atom, the more acidic the central atom, the more acidic the hydrogen.hydrogen.

HClOHClO44 > HClO > HClO33 > HClO > HClO22 > HClO > HClO

Remember that the H is attached to Remember that the H is attached to an oxygen atom.an oxygen atom.

The oxygens are electronegativeThe oxygens are electronegativePull electrons away from hydrogenPull electrons away from hydrogen


Electron Density

Cl O H


Electron Density

Cl O HO


Cl O H

O

O

Electron Density


Cl O H

O

O

O

Electron Density

Hydrated metalsHydrated metals

Highly charged Highly charged metal ions pull metal ions pull the electrons of the electrons of surrounding surrounding water molecules water molecules toward them.toward them.

Make it easier Make it easier for Hfor H++ to come to come off.off.

Al+3 OH

H

Acid-Base Properties of Acid-Base Properties of OxidesOxides

Non-metal oxides dissolved in water Non-metal oxides dissolved in water can make acids.can make acids.

SOSO33 (g) + H (g) + H22O(l) O(l) H H22SOSO44(aq)(aq)

Ionic oxides dissolve in water to Ionic oxides dissolve in water to produce bases.produce bases.

CaO(s) + HCaO(s) + H22O(l) O(l) Ca(OH) Ca(OH)22(aq)(aq)

Lewis Acids and BasesLewis Acids and Bases

Most general definition.Most general definition.Acids are electron pair acceptors.Acids are electron pair acceptors.Bases are electron pair donors.Bases are electron pair donors.

B FF

F

:NH

H

H


Boron triflouride wants more Boron triflouride wants more electrons.electrons.

B FF

F

:NH

H

H


Boron triflouride wants more Boron triflouride wants more electrons.electrons.

BFBF33 is Lewis base NH is Lewis base NH33 is a Lewis Acid. is a Lewis Acid.

BF

F

F

N

H

H

H


Al+3 ( )H

HO

Al ( )6

H

HO

+ 6

+3

arrhenius definition

Documents

h equilibrium

written h

h weak acidska

h3o oh

neutral solution h

proton h donor

logh oh

weak acid percent dissociation