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 And acid is an proton (HAnd 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 pairs.Acids and bases always come in 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 KAcid dissociation constant Kaa The equilibrium constant for the general The equilibrium constant for the general equation.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 KAcid dissociation constant Kaa HA(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 Ogroup -COOH with the H attached to O 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 small As pH decreases, [HAs pH decreases, [H++] increases ] increases

exponentiallyexponentially Sig 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 figs pOH= -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 + pOH

KKWW = 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 any one of these we can find the Given any one of these we can find the other three.other three.

ProblemsProblems If a solution has a [HIf a solution has a [H++] of .0035M what ] of .0035M what

is the pH?is the pH?

[OH[OH--]?]?

pOH?pOH?

ProblemsProblems If a solution has a pOH of 9.28 what is If a solution has a pOH of 9.28 what is

the [Hthe [H++]?]?

If a solution has a pH of 9.28 what is the If a solution has a pH of 9.28 what is the [OH[OH--]?]?

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

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. 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 will

come from the acid or the water.come from the acid or the water.

Compare KCompare Kaa or K or Kww Rest is just like last chapter.Rest is just like last chapter.

ExampleExample Calculate the pH of 1.6 M HCl(aq)Calculate the pH of 1.6 M HCl(aq) Calculate the pH of 1.6 x 10Calculate the pH of 1.6 x 10-10-10 M M

HCl(aq)HCl(aq)

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 acid will predominate.The stronger acid will predominate. Bigger Ka if concentrations are Bigger Ka if concentrations are

comparablecomparable Calculate the pH of a mixture 1.20 M HF Calculate the pH of a mixture 1.20 M HF

(Ka = 7.2 x 10(Ka = 7.2 x 10-4-4) and 3.4 M HOC) and 3.4 M HOC66HH55 (Ka (Ka

= 1.6 x 10= 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 ChâtelierLe Châtelier

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 solution? 8.1 % dissociated as 0.100 M solution?

BasesBases The OHThe OH--

is a strong base. is a strong base. Hydroxides of the alkali metals are Hydroxides of the alkali metals are

strong bases because they dissociate strong bases because they dissociate completely when dissolved.completely when dissolved.

The hydroxides of alkaline earths The hydroxides of alkaline earths Ca(OH)Ca(OH)22 etc. are strong dibasic bases, etc. are strong dibasic bases,

but they don’t dissolve well in water.but they 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 M Calculate the pH of a solution of 4.0 M pyridinepyridine (K(Kbb = 1.7 x 10 = 1.7 x 10-9-9))

Polyprotic acidsPolyprotic acids Always dissociate stepwise.Always dissociate stepwise. The first HThe first H++ comes of much easier than comes of much easier than

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

Ka for the second.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--

1010

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

the second dissociation.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 M Calculate the concentrations in a 2.0 M solution of Hsolution of H22SOSO44

Calculate the concentrations in a 2.0 x Calculate the concentrations in a 2.0 x 1010-3-3 M solution of H M solution of H22SOSO44

Salts as acids and basesSalts as acids and bases Salts are ionic compounds.Salts are ionic compounds. Salts of the cation of strong bases and Salts of the cation of strong bases and

the anion of strong acids are neutral.the anion of strong acids are neutral. for example NaCl, KNOfor example NaCl, KNO33

There is no equilibrium for strong acids There is no equilibrium for strong acids and bases.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 – solution is basic.of a weak acid – solution is basic. 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- - ]]

For HF- the acid form- Ka = [HFor HF- the acid form- Ka = [H++][F][F--]] [HF] [HF]

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

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

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

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

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

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

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

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

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

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

[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 base.The anion of a weak acid is a weak base. Calculate the pH of a solution of 1.00 M Calculate the pH of a solution of 1.00 M

NaF. Ka of HF is 7.2 x 10NaF. Ka of HF is 7.2 x 10-4-4 HH++ + F + F-- HF HF The FThe F-- ion competes with OH ion competes with OH-- for the H for the 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 acidic.the anion of a strong acid will be acidic. The same development as bases leads to The same development as bases leads 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 of Anion of weak acid, cation of weak baseweak base

KKaa > K > Kb b acidicacidic

KKaa < K < Kb b basicbasic

KKaa = K = Kb b NeutralNeutral

NHNH44CNCN

– Ka for HCN is 6.2 x 10-10

– Kb for NH3 is 1.8 x 10-5

Structure and Acid base Structure and Acid base PropertiesProperties

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

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

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

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

Strength of oxyacidsStrength of oxyacids The more oxygen hooked to the central The more oxygen hooked to the central

atom, the more acidic the hydrogen.atom, the more acidic the hydrogen. HClOHClO44 > HClO > HClO33 > HClO > HClO22 > HClO > HClO

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

The oxygens are electronegativeThe oxygens are electronegative Pull electrons away from hydrogenPull electrons away from hydrogen

Strength of oxyacidsStrength of oxyacids

Electron Density

Cl O H

Strength of oxyacidsStrength of oxyacids

Electron Density

Cl O HO

Strength of oxyacidsStrength of oxyacids

Cl O H

O

O

Electron Density

Strength of oxyacidsStrength of oxyacids

Cl O H

O

O

O

Electron Density

Hydrated metalsHydrated metals Highly charged metal Highly charged metal

ions pull the electrons ions pull the electrons of surrounding water of surrounding water molecules toward molecules toward them.them.

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

Make solution acidicMake solution acidic

Al+3 OH

H

Acid-Base Properties of OxidesAcid-Base Properties of Oxides 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. (metal oxides)produce bases. (metal oxides)

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

HydroxidesHydroxides

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

Lewis Acids and BasesLewis Acids and Bases Boron triflouride wants more electrons.Boron triflouride wants more electrons.

B FF

F

:NH

H

H

Lewis Acids and BasesLewis Acids and Bases Boron triflouride wants more electrons.Boron triflouride wants more 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

Lewis Acids and BasesLewis Acids and Bases

Al+3 ( )H

HO

Al ( )6

H

HO

+ 6

+3