Acid Base EquilibriaAcid Base Equilibria Acids and bases are found in many Acids and bases are found in many

common substances and are common substances and are important in life processes.important in life processes.

Group Work: Group Work: Make a list of some Make a list of some common acids and bases. How do common acids and bases. How do we know which is which?we know which is which?

There are several models for what There are several models for what constitutes an acid or a base -- constitutes an acid or a base -- three models to be discussed.three models to be discussed.

14.1 Acids and Bases: A Brief 14.1 Acids and Bases: A Brief ReviewReview

14.1 Acids and Bases: A Brief 14.1 Acids and Bases: A Brief ReviewReview

Acid:Acid: Base: Base:tastes sour tastes bitterstings skin feels slipperycorrosive to metals

releases CO2 from carbonatesturns litmus red turns litmus blueturns phenolphthalein colorless turns ph. pink

React together to form a salt with loss of React together to form a salt with loss of the characteristic acid/base propertiesthe characteristic acid/base properties

Arrhenius DefinitionArrhenius Definition Acids produce hydrogen ions (HAcids produce hydrogen ions (H++ ) )

in aqueous solution.in aqueous solution. Bases produce hydroxide ions Bases produce hydroxide ions

(OH(OH--) when dissolved in water.) when 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.

Arrhenius DefinitionArrhenius Definition Not realistic: HNot realistic: H++ has a radius of 10 has a radius of 10--1313

cm, which gives a very concentrated cm, which gives a very concentrated charge, so it associates with Hcharge, so it associates with H22O as O as H(HH(H22O)O)44

++, which we usually simplify , which we usually simplify to Hto H33OO++ or H or H++ (aq)(aq)

OHOH–– is also associated with H is also associated with H22O as O as OH(HOH(H22O)O)33

– – which we usually write as which we usually write as OHOH––(aq).(aq).

Bronsted-Lowry DefinitionsBronsted-Lowry Definitions And acid is an proton (HAnd acid is an proton (H++) donor and ) donor and

a base is a proton acceptor.a 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

Acid/Base PairsAcid/Base Pairs 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/Base Pairs – Group WorkAcid/Base Pairs – Group Work Write a balanced equation showing how the Write a balanced equation showing how the

following substances behave as acids in following substances behave as acids in water and identify the conjugate acid-base water and identify the conjugate acid-base pairs.pairs.HNO3 HCO3

- H3PO4 H2PO4-

HNOHNO33(aq) + H(aq) + H22O(l) O(l) ⇌⇌ H H33OO++ (aq) + NO(aq) + NO33--(aq)(aq)

HCOHCO33--(aq) + H(aq) + H22O(l) O(l) ⇌⇌ H H33OO++ (aq) + CO(aq) + CO33

22--(aq)(aq) HH33POPO44(aq) + H(aq) + H22O(l) O(l) ⇌⇌ H H33OO++ (aq) + H(aq) + H22POPO44

--(aq)(aq) HH22POPO44

--(aq) + H(aq) + H22O(l) O(l) ⇌⇌ H H33OO++ (aq) + HPO(aq) + HPO4422--(aq)(aq)

acid 1 base 2 acid 2 base 1acid 1 base 2 acid 2 base 1

AcidAcid BaseBaseStrongestStrongestHClOHClO44 ClOClO44

-- WeakestWeakest acidsacids HH22SOSO44 HSOHSO44

-- basesbasesHIHI II--

HBrHBr BrBr--

HClHCl ClCl--

HNOHNO33 NONO33--

H3O+ H2O

HSOHSO44-- SOSO44

22--

HH22SOSO33 HSOHSO33--

HH33POPO44 HH22POPO44--

HNOHNO22 NONO22--

HFHF FF--

CHCH33COCO22HH CHCH33COCO22--

HH22COCO33 HCOHCO33--

HH22SS HSHS--

NHNH44++ NHNH33

HCNHCN CNCN--

HCOHCO33-- COCO33

22--

HSHS-- SS22--

H2O OH-

WeakestWeakest NHNH33 NHNH22-- StrongestStrongest

acidsacids OHOH-- OO22-- bases bases

back

Leveling EffectLeveling EffectLeveling EffectLeveling Effect

All acids above HAll acids above H33OO++ in the table are in the table are strong acids, which dissociate strong acids, which dissociate completely in aqueous solution.completely in aqueous solution.

All bases below OHAll bases below OH-- in the table are in the table are strong bases, which dissociate strong bases, which dissociate completely in aqueous solution.completely in aqueous solution.

The table can be used to make The table can be used to make predictions, based on the principle that predictions, based on the principle that the stronger acid reacts with the the stronger acid reacts with the stronger base to form a weaker acid stronger base to form a weaker acid and a weaker base.and a weaker base.

Predicting Acid-Base ReactionsPredicting Acid-Base ReactionsPredicting Acid-Base ReactionsPredicting Acid-Base Reactions HCl + HSOHCl + HSO33

-- ⇌⇌ H H22SOSO33 + Cl + Cl--

stronger stronger weaker stronger stronger weaker weakerweakeracid base acid base

We must also consider HWe must also consider H22O as a O as a possible acid or base. Thus, HNOpossible acid or base. Thus, HNO33 will transfer its proton to Hwill transfer its proton to H22O, not O, not to Clto Cl-- because H because H22O is a stronger O is a stronger base than Clbase than Cl--..

Group WorkGroup WorkGroup WorkGroup Work Write an equation showing the Write an equation showing the

position of equilibrium for the position of equilibrium for the following mixtures. Remember that following mixtures. Remember that HH22O can also be either an acid or a O can also be either an acid or a base.base.HSO4

- and F-

HS- and HCO3-

HSOHSO44-- + F + F-- ⇌⇌ SO SO44

22-- + HF + HF

HSHS-- + HCO + HCO33-- ⇌⇌HH22S + COS + CO33

22--

14.2 Acid dissociation constant K14.2 Acid dissociation constant Kaa The 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 ignoring

the water in equation (it is implied).the 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 We can write the expression for

any acid.any 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 ] is equal to [HA][HA]

AA-- is a weaker is a weaker base than waterbase than 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 Polyprotic Acids- more than 1

acidic hydrogen (diprotic, triprotic).acidic hydrogen (diprotic, triprotic). Oxyacids - Proton is attached to Oxyacids - Proton is attached to

the oxygen of an ion.the oxygen of an ion. Organic acids contain the Carboxyl Organic acids contain the Carboxyl

group -COOH with the H attached group -COOH with the H attached to Oto 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--]]

14.3 pH Scale14.3 pH Scale pH= -log[HpH= -log[H++]] Used because [HUsed because [H++] is usually very ] is usually very

smallsmall As pH decreases, [HAs pH decreases, [H++] increases ] increases

exponentiallyexponentially Sig figs only the digits after the Sig figs only the digits after the

decimal place of a pH are significantdecimal place 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

Measuring pHMeasuring pHMeasuring pHMeasuring pH

litmus or pH paperlitmus or pH paper

color changes of indicatorscolor changes of indicators

voltage generated by voltage generated by

electrodes (pH meter)electrodes (pH meter)

pH IndicatorspH Indicators

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

So…So… 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 other three through equilibrium relationships (Kw)

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

14.5 pH and K14.5 pH and Kaa of Acid Solutions of Acid Solutions Always write down the major ions Always write down the major ions

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

one way to do this. Apply good one way to do this. Apply good chemistry!chemistry!

Strong Acid: HNOStrong Acid: HNO33Strong Acid: HNOStrong Acid: HNO33

HNOHNO33 is completely dissociated into is completely dissociated into the ions, Hthe ions, H33OO++ and NO and NO33

- - (work sample (work sample 14.7)14.7)

Strong AcidsStrong Acids HBr, HI, HCl, HNOHBr, HI, HCl, HNO33, H, H22SOSO44, HClO, HClO44

ALWAYS WRITE THE MAJOR ALWAYS WRITE THE MAJOR SPECIESSPECIES

Completely dissociatedCompletely dissociated [H[H++] = [HA]] = [HA]ii

[OH[OH--] is going to be small because ] is going to be small because of equilibriumof equilibriumKw = 10-14 = [H+][OH-]

Changes in pH with DilutionChanges in pH with DilutionChanges in pH with DilutionChanges in pH with Dilution

Group Work: pH for factors of 10 Group Work: pH for factors of 10 dilution?dilution?

What is the pH of 1.0 M HCl?What is the pH of 1.0 M HCl? pH = 0.00pH = 0.00 What is the pH of 0.10 M HCl (a 1:10 dilution)?What is the pH of 0.10 M HCl (a 1:10 dilution)? pH = 1.00pH = 1.00 What is the pH of 0.010 M HCl?What is the pH of 0.010 M HCl? pH = 2.00pH = 2.00

pHondilution28.mov.lnk

Changes in pH with DilutionChanges in pH with DilutionChanges in pH with DilutionChanges in pH with Dilution What is the pH of 1.0 x 10What is the pH of 1.0 x 10--3 3 M HCl?M HCl? pH = 3.00pH = 3.00 What is the pH of 1.0 x 10What is the pH of 1.0 x 10- - 4 4 M HCl?M HCl? pH = 4.00pH = 4.00 What is the pH of 1.0 x 10What is the pH of 1.0 x 10--5 5 M HCl?M HCl? pH = 5.00pH = 5.00 What is the pH of 1.0 x 10What is the pH of 1.0 x 10--6 6 M HCl?M HCl? pH = 5.996pH = 5.996

pHondilution28.mov.lnk

Changes in pH with DilutionChanges in pH with DilutionChanges in pH with DilutionChanges in pH with Dilution What is the pH of 1.0 x 10What is the pH of 1.0 x 10--7 7 M HCl?M HCl? pH = 6.791pH = 6.791 What is the pH of 1.0 x 10What is the pH of 1.0 x 10--8 8 M HCl?M HCl? pH = 6.996pH = 6.996 Why does the pH stop changing at a Why does the pH stop changing at a

value of about 7?value of about 7? Water has a pH of 7 due to Water has a pH of 7 due to

autodissociation, so it is never possible autodissociation, so it is never possible to get a pH higher than 7 by addition of to get a pH higher than 7 by addition of water.water.– If [HA] < 10-7 water contributes the H+

14.5 pH of Weak Acids14.5 pH of Weak Acids14.5 pH of Weak Acids14.5 pH of Weak Acids Except for the strong acids, most Except for the strong acids, most

acids do not ionize completely. acids do not ionize completely. These acids are called These acids are called weak acidsweak acids..

HF(aq) + HHF(aq) + H22O(l) O(l) ⇌⇌ H H33OO++(aq) + F(aq) + F--

(aq)(aq)04m07an1.mov.lnk

14.5 pH of Weak Acids14.5 pH of Weak Acids KKaa will be small. 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 KCompare Kaa or K or Kww

Rest is just like chapter 13.Rest is just like chapter 13.

ExampleExample Calculate the pH of 2.0 M acetic Calculate the pH of 2.0 M acetic

acid HCacid HC22HH33OO22 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 KBigger Kaa ifif concentrations are concentrations are

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

M HF (Ka = 7.2 x 10M HF (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) )

Some Weak AcidsSome Weak Acids

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 0.100 M Acetic acidand 0.100 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 Chatelier principle with dilution (pg 642)

The other wayThe other way What is the Ka of a weak acid What is the Ka of a weak acid

that is 8.1 % dissociated as 0.100 that is 8.1 % dissociated as 0.100 M solution? M solution?

Compare to Sample Exercise Compare to Sample Exercise 14.1114.11

pH and KapH and KapH and KapH and Ka One way to find the value of KOne way to find the value of Kaa for a for a

weak acid is using concentration & pH weak acid is using concentration & pH data. data.

The pH of 0.500 M HNOThe pH of 0.500 M HNO22 is 1.827. What is 1.827. What is Kis Kaa of HNO of HNO22??

[H[H33OO++] = 10] = 10--1.8271.827 = 0.0149 M = 0.0149 M HNOHNO22 + H + H22O O H H33OO+ + + + NONO22

--

II 0.5000.500 ---- 00 0 0CC -0.0149-0.0149 +0.0149 +0.0149 +0.0149 +0.0149EE 0.4850.485 0.0149 0.0149 0.0149 0.0149

KKaa = [H = [H33OO++][NO][NO22--]/[HNO]/[HNO22]]

KKaa = (0.0149) = (0.0149)22/0.485 = 4.58 x 10/0.485 = 4.58 x 10--44

14.6 Bases14.6 Bases 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 etc. are strong dibasic

bases, but they don’t dissolve well in bases, but they don’t dissolve well in water.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 Hydroxides are strong.Hydroxides are strong. Others are weak.Others are weak. Smaller Smaller KKbb = weaker base. = weaker base.

Consider a solution of 4.0 M Consider a solution of 4.0 M pyridinepyridine (Kb = 1.7 x 10(Kb = 1.7 x 10-9-9))

– What are the major species present in solution?– Determine the [OH-] and pH of the solution.

N:

14.7 Polyprotic acids14.7 Polyprotic acids Always dissociate stepwise.Always dissociate stepwise. Denoted KaDenoted Ka11, Ka, Ka22, Ka, Ka33, etc… (Table , etc… (Table

14.4)14.4) HH22COCO33 + H + H22O HO H++ + HCO + HCO33

--

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

HCOHCO33- - + H+ H22O O H H++ + CO + CO33

-2-2

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

Conjugate base in 1Conjugate base in 1stst step is acid in 2 step is acid in 2ndnd..

Polyprotic Acid ObservationsPolyprotic Acid Observations

The first HThe first H++ comes of much easier comes of much easier than the second.than the second.

KKaa for the first step is much bigger for the first step is much bigger than Kthan Kaa for the second. for the second.

Calculate the Concentration…Calculate the Concentration… ……of all the ions in a solution of of all the ions in a solution of

5.00 M sulfurous acid.5.00 M sulfurous acid.KaKa11 = 1.5 x 10 = 1.5 x 10-2-2

KaKa22 = 1.0 x 10 = 1.0 x 10-7-7

Find the pH of the solutionFind the pH of the solution

See Sample Exercise 14.15 for See Sample Exercise 14.15 for another example.another example.

Sulfuric acid, an interesting caseSulfuric acid, an interesting case Calculate the pH and concentration of Calculate the pH and concentration of

all species in a 1.5 M solution of Hall species in a 1.5 M solution of H22SOSO44 – Pg 651, Table 14.4 contains Ka’s for polyprotics

Calculate the concentrations in a Calculate the concentrations in a 1.5 x 101.5 x 10-2-2 M solution of H M solution of H22SOSO44

See Sample Exc. 14.16 & 17See Sample Exc. 14.16 & 17 Summary pg. 655Summary pg. 655

– In first step H2SO4 is a strong acid.

– 2nd step, it is a weak acid: Ka2 = 1.2 x 10-2

14.8 Acid/Base Properties of Salts14.8 Acid/Base Properties of Salts Salts are ionic compounds.Salts are ionic compounds.

– Recall Model: Ionic compounds dissociate into ions in solution. The ions move around independently.

These cations and anions can (but These cations and anions can (but do not have to!) act as acids or do not have to!) act as acids or bases depending on how they bases depending on how they react with water (referred to as a react with water (referred to as a hydrolysis reaction)hydrolysis reaction)

Ch 14, #99 discuss on WB’sCh 14, #99 discuss on WB’s

Salts that make Neutral SolutionsSalts that make Neutral Solutions Salts containing the cation from a Salts containing the cation from a

strong base and the anion from a strong base and the anion from a strong acid are neutral.strong acid are neutral.

Hydrolysis is not observed with ions Hydrolysis is not observed with ions derived from strong acids or bases:derived from strong acids or bases:Cations of group I and II (except Be2+)

Anions: Cl-, Br-, I-, NO3-, ClO4

-

for example NaCl, KNOfor example NaCl, KNO33 There is no equilibrium established There is no equilibrium established

from these ions.from these ions.

Basic SaltsBasic Salts If the If the anionanion of a salt is the conjugate of a salt is the conjugate

base of a weak acid the solution will be base of a weak acid the solution will be basic.basic.

Consider an aqueous solution of NaFConsider an aqueous solution of NaF The aqueous species are NaThe aqueous species are Na++, F, F--, and , and

HH22OO

FF- - + H+ H22O O HF + OHHF + OH--

The equilibrium constant for hydrolysis The equilibrium constant for hydrolysis is just a Kis just a Kaa or K or Kbb, depending on the type , depending on the type of hydrolysis.of hydrolysis.

Basic SaltsBasic Salts 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]

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

pH of Basic SaltspH of Basic Salts The anion of a weak acid is a weak The anion of a weak acid is a weak

base.base. The CNThe CN-- ion competes with OH ion competes with OH-- for for

the Hthe H+ +

Relative base strength:Relative base strength:

OHOH-- > CN > CN-- > H > H22OO Calculate the pH of a solution of Calculate the pH of a solution of

1.00 M NaCN. 1.00 M NaCN. Ka of HCN is 6.2 x 10Ka of HCN is 6.2 x 10-10-10

Acidic saltsAcidic salts If the If the cationcation of a salt is the conjugate of a salt is the conjugate

acid of a weak base the solution will be acid of a weak base the solution will be acidic.acidic.

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.

Acidic Salts – Metal ionsAcidic Salts – Metal ionsAcidic Salts – Metal ionsAcidic Salts – Metal ions Ions are often modified when dissolved Ions are often modified when dissolved

in solution. Examine the photos of in solution. Examine the photos of Fe(III) salts and solutions. Why do they Fe(III) salts and solutions. Why do they have different colors?have different colors?

Fe(NOFe(NO33))33..6H6H22O contains pink Fe(HO contains pink Fe(H22O)O)66

33++

Solutions may hydrolyze to give yellow Solutions may hydrolyze to give yellow Fe(HFe(H22O)O)55OHOH22++ or even reddish brown or even reddish brown Fe(HFe(H22O)O)33(OH)(OH)33

FeClFeCl33..6H6H22O contains ions such as yellow O contains ions such as yellow Fe(HFe(H22O)O)55ClCl22++

Hydrolysis of MetalsHydrolysis of Metals Hydrolysis is more Hydrolysis is more

important for more important for more highly charged highly charged ions and smaller ions and smaller ions.ions.

Hydrogen from Hydrogen from water easier to water easier to remove.remove.

Hydrolysis of MetalsHydrolysis of Metals Table below gives values of KTable below gives values of Kaa for metal ions: for metal ions:

IonIon RadiusRadius KaKa NaNa++ 95 pm95 pm 3.3 x 103.3 x 10--1515

Li+ 60 pm 1.5 x 10-14

Be2+ 31 pm 3.2 x 10-7

Mg2+ 65 pm 3.8 x 10-12

Ba2+ 135 pm 1.5 x 10-14

Cr3+ 69 pm 9.8 x 10-5

Zr4+ 78 pm 6.0 x 10-1

Greater values of KGreater values of Kaa for ions with larger for ions with larger charge and smaller size.charge and smaller size.

Hydrolysis of MetalsHydrolysis of Metals Calculate the pH of a 0.20 M CrClCalculate the pH of a 0.20 M CrCl33

solution. (From the table, the Ka solution. (From the table, the Ka value for Crvalue for Cr3+3+ is 9.8 x 10 is 9.8 x 10-5-5))

Anion of weak acid, cation of weak baseAnion of weak acid, cation of weak base If both of the ions have acid/base If both of the ions have acid/base

properties, compare the Ka of the properties, compare the Ka of the cation to the Kb of the anion cation to the Kb of the anion

KKaa > K > Kb b acidicacidic KKaa < K < Kb b basicbasic KKaa = K = Kb b neutralneutral Predict whether an aqueous Predict whether an aqueous

solution of ammonium cyanide will solution of ammonium cyanide will be acidic, basic, or neutral.be acidic, basic, or neutral.

Summary Table 14.6, pg 660Summary Table 14.6, pg 660

14.9 Structure and Acid base 14.9 Structure and Acid base PropertiesProperties

Draw lewis structures (that obey octet Draw lewis structures (that obey octet rule) for the following oxyacids.rule) for the following oxyacids.

HClOHClO44 KKaa = Large (~10 = Large (~1077))

HClOHClO33 KKaa = ~1 = ~1

HClOHClO22 KKaa = 1.2 x 10 = 1.2 x 10 –2–2

HClOHClO KKaa = 3.5 x 10 = 3.5 x 10 –8–8 Can you explain the relative strengths of Can you explain the relative strengths of

these acids using your knowledge of these acids using your knowledge of atomic structure and bonding?atomic structure and bonding?

Strength of oxyacidsStrength of oxyacids

Cl O H

O

O

O

Electron Density

Strength of oxyacidsStrength of oxyacids

Cl O H

O

O

Electron Density

Strength of oxyacidsStrength of oxyacids

Electron Density

Cl O HO

Strength of oxyacidsStrength of oxyacids

Electron Density

Cl O H

Strength of oxyacidsStrength of oxyacids The more oxygen bonded to the The more oxygen bonded to the

central atom, the more acidic the central atom, the more acidic the hydrogen.hydrogen.

The oxygens are electronegativeThe oxygens are electronegative Pulls electron density away from Pulls electron density away from

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

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

14.9 Structure and Acid base 14.9 Structure and Acid base PropertiesProperties

Draw lewis structures (that obey octet Draw lewis structures (that obey octet rule) for the following oxyacids.rule) for the following oxyacids.

HOClHOCl KKaa = 4 x 10 = 4 x 10 –8–8

HOBrHOBr KKaa = 2 x 10 = 2 x 10 –9–9

HOIHOI KKaa = 2 x 10 = 2 x 10 –11–11

HOCH3HOCH3 KKaa = ~ 10 = ~ 10 –15–15 Can you explain the relative strengths of Can you explain the relative strengths of

these acids using your knowledge of these acids using your knowledge of atomic structure and bonding?atomic structure and bonding?

14.9 Structure and Acid base 14.9 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 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 -stronger The more polar H-O-X bond -stronger acid.acid.

14.10 Acid-Base Properties of 14.10 Acid-Base Properties of OxidesOxides

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

14.11 Lewis Acids and Bases14.11 Lewis 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 Boron triflouride wants more

electrons.electrons.

B FF

F

:NH

H

H

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

electrons.electrons. BFBF33 is Lewis acid NH is Lewis acid NH33 is a Lewis is a Lewis

base. base.

BF

F

F

N

H

H

H

Lewis Acids and BasesLewis Acids and Bases

Al+3 ( )H

HO

Al ( )6

H

HO

+ 6

+3