Ch. 14: Acids and Bases 14.1 Intro to Acids and Bases 14.2 Acid Strength 14.3 pH Scale

Ch. 14: Acids and Ch. 14: Acids and BasesBases

14.1 Intro to Acids and Bases14.1 Intro to Acids and Bases

14.2 Acid Strength14.2 Acid Strength

14.3 pH Scale14.3 pH Scale

DefinitionsDefinitions

ArrheniusArrhenius ______: produce H+ in aqueous solution______: produce H+ in aqueous solution ______: produces OH- in aqueous ______: produces OH- in aqueous

solutionsolution very limitedvery limited

Bronsted-LowryBronsted-Lowry ______: H+ donor______: H+ donor ______: H+ acceptor______: H+ acceptor more generalmore general

Conjugate Acid-Base PairConjugate Acid-Base Pair

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

2 substances that are connected by a 2 substances that are connected by a donating and accepting of Hdonating and accepting of H22OO

really a “fight” over Hreally a “fight” over H++ between two between two bases: ______ and ______bases: ______ and ______ if A- has a greater attraction, rxn lies to _____if A- has a greater attraction, rxn lies to _____ if Hif H22O has greater attraction, rxn lies to _____O has greater attraction, rxn lies to _____

This helps with #29 on HWThis helps with #29 on HW

Acid dissociation constant (KAcid dissociation constant (Kaa))

equilibrium expression where Hequilibrium expression where H++ is is removed to form conjugate baseremoved to form conjugate base

HA + HHA + H22O O ⇄⇄ H H33OO++ + A + A--

Don’t include HDon’t include H22OO

aK

StrengthStrength determined by equilibrium position of determined by equilibrium position of

dissociation reactiondissociation reaction strong acid: strong acid:

lies far to right, almost all HA is _____________.lies far to right, almost all HA is _____________. ________________________________ creates weak conjugate basecreates weak conjugate base

weak acid: weak acid: lies far to left, almost all HA is stays as _____.lies far to left, almost all HA is stays as _____. ________________________________ creates strong conjugate basecreates strong conjugate base

This helps with #33 on HWThis helps with #33 on HW

Water is a stronger base than the CB of a strong acid but a weaker base than the CB of a weak acid

Water is a stronger acid than the CA or a strong base but a weaker acid than the CA if a weak base

Types of AcidsTypes of Acids

__________: an acid with 2 acidic protons__________: an acid with 2 acidic protons __________: ex. HNO__________: ex. HNO33

most acids are this typemost acids are this type where the acidic proton is attached to an where the acidic proton is attached to an

oxygenoxygen

_________________: ex. CH_________________: ex. CH33COOHCOOH containing a carboxyl groupcontaining a carboxyl group usually weakusually weak

_________________: ex. HBr_________________: ex. HBr hydrogen and a halogenhydrogen and a halogen

AutoionizationAutoionization

2 water molecules exchange H2 water molecules exchange H++

HH22O + HO + H22O O ⇄⇄ H H33OO++ +OH +OH--

KKww== dissociation constant for waterdissociation constant for water

at 25C, [Hat 25C, [H++]=[OH]=[OH--]=1.0 x 10]=1.0 x 10-7-7

so at 25C, Kso at 25C, Kww=1.0x10=1.0x10-14-14

How will change it with temperature?How will change it with temperature?

pH scalepH scale pH=pH= pOH=pOH= [H[H++]=]= [OH[OH--]=]= pH ____________ as [HpH ____________ as [H++] ]

____________________________ pH + pOH = _____pH + pOH = _____ This helps with #37, 41, 43 on HWThis helps with #37, 41, 43 on HW

Example 1Example 1

Write the ionization or dissociation Write the ionization or dissociation reaction and the Kreaction and the Kaa expression for expression for each of the following:each of the following:

acetic acid – (HCHacetic acid – (HCH33COO)COO)

ammonium ion – (NHammonium ion – (NH44++))

Example 2Example 2

Determine the acid, base, conj. acid, and Determine the acid, base, conj. acid, and conj. base in each reaction:conj. base in each reaction:

NHNH44++(aq) + CN(aq) + CN--(aq) (aq) ⇄⇄ HCN(aq) + NH HCN(aq) + NH33(aq(aq

(CH(CH33))33N(aq) + HN(aq) + H22O(l) O(l) ⇄⇄ (CH (CH33))33NHNH++(aq) + OH(aq) + OH--(aq)(aq)

HCHOHCHO22(aq) + PO(aq) + PO443-3-(aq) (aq) ⇄⇄ CHO CHO22

--(aq) + HPO(aq) + HPO442-2-(aq)(aq)

Example 3Example 3 Determine which species is a Determine which species is a

stronger base: F- or Cl-stronger base: F- or Cl-

Determine which species is a Determine which species is a stronger acid: Hstronger acid: H22O or NHO or NH44

++

Example 4Example 4

The [OH-] of a solution at 25C is 1.0 x The [OH-] of a solution at 25C is 1.0 x 1010-5-5 M. Determine the [H M. Determine the [H++], pH and ], pH and pOH.pOH.

Example 5Example 5

The pH of a solution at 25C is 5.77. The pH of a solution at 25C is 5.77. Calculate the pOH, [OH-] and [H+].Calculate the pOH, [OH-] and [H+].


14.4-5 pH of Acidic Solutions 14.4-5 pH of Acidic Solutions

Strong AcidsStrong Acids SA completely form ions so you do not need SA completely form ions so you do not need

to use Ka and I-C-E chartto use Ka and I-C-E chart Finding the pH of 0.10 M HNOFinding the pH of 0.10 M HNO33

Always write the important species Always write the important species present at the beginning of each problempresent at the beginning of each problem

HH++ , NO , NO33--, H, H22OO

water will exist as H+ and OH- but only a water will exist as H+ and OH- but only a small amount- so it can be ignoredsmall amount- so it can be ignored

HNOHNO3 3 H H++ + NO + NO33--

[H[H++] = 0.10 M] = 0.10 M pH = -log(0.10) = 1.00pH = -log(0.10) = 1.00

Strong AcidsStrong Acids

Find the pH of 1.0 x 10Find the pH of 1.0 x 10-10-10 M HCl M HCl

Weak AcidsWeak Acids

1.1. Write major speciesWrite major species

2.2. Decide on which can provide HDecide on which can provide H++ ions ions

3.3. Make ice chartMake ice chart

4.4. Put equilibrium values in KPut equilibrium values in Kaa expressionexpression

5.5. Check validity of assumption (x Check validity of assumption (x must be less than 5% of initial conc)must be less than 5% of initial conc)

6.6. Find pHFind pH

Weak Acids- ExampleWeak Acids- Example

Calculate the pH of 1.00 M solution of Calculate the pH of 1.00 M solution of HF (KHF (Kaa = 7.2 x 10 = 7.2 x 10-4-4))

Weak Acids- ExampleWeak Acids- Example HF HF H H++ + F + F--

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Weak Acids- ExampleWeak Acids- Example

Check assumption:Check assumption:

pH =pH =

Weak Acid- Example 2Weak Acid- Example 2

Find pH of 0.100 M solution of HOCl (Ka = Find pH of 0.100 M solution of HOCl (Ka = 3.5x103.5x10-8-8)) HOCl, HHOCl, H22OO HOCl will provide much more HHOCl will provide much more H++ than than

HH22O – ignore HO – ignore H22OO

HOCl HOCl H H++ + OCl + OCl--

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Weak Acid- Example 2Weak Acid- Example 2

Check assumption:Check assumption:

pH =pH =

Mixtures of Weak AcidsMixtures of Weak Acids

When dealing with a mixture of acids, When dealing with a mixture of acids, consider the strongest acid firstconsider the strongest acid first

then, use the “Equilibrium” values from then, use the “Equilibrium” values from it to begin your weaker acidit to begin your weaker acid


Find the pH of a mixture of 1.00 M Find the pH of a mixture of 1.00 M HCN (KHCN (Kaa=6.2x10=6.2x10-10-10) and 5.00 M HNO) and 5.00 M HNO22 (K(Kaa=4.0x10-=4.0x10-44)) HNOHNO22 is most important b/c it has is most important b/c it has

highest Ka valuehighest Ka value

HNOHNO22 H H++ + NO + NO22--

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HCN HCN H H++ + CN + CN-- II

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[H[H++]=]= pH =pH =

Find the [CNFind the [CN--] at equilibrium] at equilibrium [CN-] =[CN-] =

Percent DissociationPercent Dissociation

also called Percent Ionizationalso called Percent Ionization

for a weak acid, the % dissociation for a weak acid, the % dissociation increases as molarity decreasesincreases as molarity decreases

dilution shifts equilibrium to side with dilution shifts equilibrium to side with greater number of particlesgreater number of particles


Calculate Percent DissociationCalculate Percent Dissociation

for 1.0 M acetic acid (Kfor 1.0 M acetic acid (Kaa=1.8x10=1.8x10-5-5))

CHCH33COOH COOH H H++ + CH + CH33COOCOO--

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nDissocatio%

100ionconcentrat initial

ddissociateamount


For 0.100 M CHFor 0.100 M CH33COOHCOOH

aK

nDissocatio%


In a 0.200 M solution of a weak In a 0.200 M solution of a weak acid, 2.5% of the acid is acid, 2.5% of the acid is dissociated. Find the Ka.dissociated. Find the Ka.

100ionconcentrat initial

ddissociateamount

HA HA H H++ + A + A--

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14.6 Bases14.6 Bases

BasesBases

BasesBases Strong BasesStrong Bases

Find pH of 5.0x10Find pH of 5.0x10-2-2 M NaOH solution M NaOH solution

What would be another way to get pH?What would be another way to get pH? What if it was a Ca(OH)What if it was a Ca(OH)22 solution? solution?

BasesBases Weak BasesWeak Bases

do not contain OHdo not contain OH--

accepts Haccepts H++ from H from H22O to make OHO to make OH--

usually have at least one unshared usually have at least one unshared pair of electronspair of electrons

used to form bond with hydrogenused to form bond with hydrogen

BasesBases

KKbb

refers to reaction of base with refers to reaction of base with water to make conjugate acid and water to make conjugate acid and OHOH--

for weak bases onlyfor weak bases only

B(aq) + OHB(aq) + OH--(l) (l) BH BH++(aq) + OH(aq) + OH--(aq)(aq)

ExampleExample

Find the pH for 15.0 M solution of Find the pH for 15.0 M solution of NHNH33 (K (Kbb = 1.8x10 = 1.8x10-5-5)) NHNH33 will create more OH- than will create more OH- than

water so autoionization can be water so autoionization can be ignoredignored NHNH33 + H + H22O O NH NH44

++ + OH + OH--

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ExampleExample

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ExampleExample Codeine (CCodeine (C1818HH2121NONO33) is a weak ) is a weak

organic base. A 5.0x10organic base. A 5.0x10-3-3 M solution of M solution of codeine has a pH of 9.95. Calculate codeine has a pH of 9.95. Calculate the Kthe Kbb for this substance. for this substance.

What is the chemical reaction?What is the chemical reaction?

ExampleExample

CC1818HH2121NONO3 3 + H+ H22O O ⇄ ⇄ HCHC1818HH2121NONO33++ + OH + OH--

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x = [OH-] = x = [OH-] = 8.9x108.9x10-5-5

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14.7 Polyprotic Acids14.7 Polyprotic Acids

Polyprotic AcidsPolyprotic Acids acids that can donate more than one H+acids that can donate more than one H+ always dissociate one at a timealways dissociate one at a time Example: carbonic acidExample: carbonic acid

KKa1a1= 4.3x10= 4.3x10-7-7

KKa2a2 = 5.6x10 = 5.6x10-11-11

KKa1a1 > K > Ka2a2 > K > Ka3a3 for for

typical weak polyprotic typical weak polyprotic

acidacid

Important Polyprotic AcidsImportant Polyprotic Acids phosphoric acid: Hphosphoric acid: H33POPO44

only 1only 1stst step creates important amount of step creates important amount of H+H+

sulfuric acid: Hsulfuric acid: H22SOSO44

11stst step is strong (H step is strong (H22SOSO44 is a strong acid) is a strong acid) 22ndnd step is weak (HSO step is weak (HSO44

-- is a weak acid) is a weak acid)

ExampleExample Find the pH of a 1.00x10Find the pH of a 1.00x10-2-2 M sulfuric acid M sulfuric acid

solutionsolution HH++, HSO, HSO44

--, H, H22OO From 1From 1stst dissociation, [H+]= dissociation, [H+]= 1.00x101.00x10-2-2 M M

HSOHSO44-- SO SO44

2-2- + H + H++

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Ch. 14 Acids and Ch. 14 Acids and BasesBases

14.8 Acidic and Basic 14.8 Acidic and Basic Properties of SaltsProperties of Salts

SaltsSalts

another word for ionic compoundsanother word for ionic compounds when soluble salts are dissolved, when soluble salts are dissolved,

they break up into ions that can be they break up into ions that can be either acidic or basiceither acidic or basic

the acidic or basic ions make the the acidic or basic ions make the solution acidic or basicsolution acidic or basic

Determining A/B of a SaltDetermining A/B of a Salt Figure out what each ion in the salt comes Figure out what each ion in the salt comes

fromfrom Ex: KCNEx: KCN

K+ comes from strong base, _______K+ comes from strong base, _______ CN- comes from weak acid, _______CN- comes from weak acid, _______

Determine what quality that gives each ionDetermine what quality that gives each ion K+ must be weak _________K+ must be weak _________ CN- must be strong _________CN- must be strong _________

Compare and determine the overall acidity Compare and determine the overall acidity or basicity of solutionor basicity of solution overall: ____________________overall: ____________________

CationsCations

Weak Conj. AcidWeak Conj. Acid from Strong Bfrom Strong B KK++, Ca, Ca2+2+

from KOH and from KOH and Ca(OH)Ca(OH)22

Strong Conj. Strong Conj. AcidAcid from weak Bfrom weak B NHNH44

++, C, C55HH55NHNH++

from NHfrom NH33 and and CC55HH55NN

and highly and highly charged metal charged metal ions (Alions (Al3+3+ or Fe or Fe3+3+))

AnionsAnions

weak Conj. Base weak Conj. Base from Strong Acidfrom Strong Acid ClCl--, HSO, HSO44

--

from HCl and from HCl and HH22SOSO44

strong Conj. strong Conj. Base Base from Weak Acidfrom Weak Acid HCOHCO33

2-2-, NO, NO22--

from Hfrom H22COCO33 and and HNOHNO22

Acidic and Basic?Acidic and Basic?

If it is difficult to tell the overall If it is difficult to tell the overall quality, compare the K values to quality, compare the K values to determine the type of solutiondetermine the type of solution

KKaa > K > Kbb : _________ : _________

KKbb > K > Kaa : _________ : _________

KKaa*K*Kbb = K = Kww

for any weak acid andfor any weak acid and

its CBits CB

PracticePractice Predict which of the following will be Predict which of the following will be

acidic, basic or neutralacidic, basic or neutral NHNH44BrBr

•NHNH44++

•BrBr-- •overall:overall:

FeClFeCl33•FeFe+3+3 •ClCl-- •overall:overall:

PracticePractice NaNa22COCO33

• NaNa++

• COCO332-2-

• overall:overall: KClOKClO44

• KK++

• ClOClO44

• overall:overall: NaHCNaHC22OO44

• NaNa++

• HCHC22OO44--

• overall:overall:

ExampleExample Find the pH of a 0.20 M solution of KF.Find the pH of a 0.20 M solution of KF.

KF KF K K++ + F + F--

which of these will effect the pH of the which of these will effect the pH of the solution?solution?

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

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SummarySummary


14.9 Structure14.9 Structure

Why are some H’s acidic?Why are some H’s acidic?

acidic:acidic: weak bondsweak bonds polar bondspolar bonds

non-acidicnon-acidic strong bondsstrong bonds nonpolar bondsnonpolar bonds

Factors in AcidityFactors in Acidity Overall: the ______________ the bond to the Overall: the ______________ the bond to the

H is, the ___________ the acid isH is, the ___________ the acid is If the atoms around the bond are more If the atoms around the bond are more

electronegative, they will pull electron electronegative, they will pull electron density away from the bonddensity away from the bond

that will make the bond weakerthat will make the bond weaker Electronegativity of halogenElectronegativity of halogen

the more electronegative the halogen the more electronegative the halogen is, the more polar the bond is, and the is, the more polar the bond is, and the stronger the acid isstronger the acid is

Factors in AcidityFactors in Acidity

Size of atomsSize of atoms the ___________ the atoms, the weaker the ___________ the atoms, the weaker

the bond, the ___________the acidthe bond, the ___________the acid Ex: H-F, H-Cl, H-Br, H-IEx: H-F, H-Cl, H-Br, H-I H-F has the most polar bond but it is a H-F has the most polar bond but it is a

weak acid- Why?weak acid- Why? H and F are both tiny atoms so have a H and F are both tiny atoms so have a

stronger attraction to each otherstronger attraction to each other H-I has very weak bond b/c I is large so H-I has very weak bond b/c I is large so

is a strong acidis a strong acid

Factors in AcidityFactors in Acidity Number of Oxygens in OxyacidNumber of Oxygens in Oxyacid

the _________ the number of the _________ the number of oxygens, the more polar the oxygens, the more polar the bond is, the _________ the acid bond is, the _________ the acid isis

ExampleExample

Which is the stronger acid? ExplainWhich is the stronger acid? Explain HNOHNO22 or HClO or HClO22

HNOHNO33 or HNO or HNO22

CClCCl33COOH or CHCOOH or CH33COOHCOOH


14.10 Oxides14.10 Oxides

H-O-XH-O-X If X is relatively electronegativeIf X is relatively electronegative

H-O bond is weaker and breaks easilyH-O bond is weaker and breaks easily

HOX HOX If X is not electronegativeIf X is not electronegative

O-X bond will breakO-X bond will break

HOX HOX

Acidic OxidesAcidic Oxides

when a covalent oxide dissolves in when a covalent oxide dissolves in water, an acidic solution formswater, an acidic solution forms

Ex: SOEx: SO22, CO, CO22, NO, NO22

how do you determine what acid is how do you determine what acid is formed?formed?

be sure the nonmetal atom keeps the be sure the nonmetal atom keeps the same oxidation statesame oxidation state

SOSO22 + H + H22O O

Basic OxidesBasic Oxides

when an ionic oxide dissolves in when an ionic oxide dissolves in water, a basic solution formswater, a basic solution forms

NaNa22O, CaO, KO, CaO, K22OO

NaNa22O + HO + H22O O


14.11 Lewis Acid-Base Model14.11 Lewis Acid-Base Model

Lewis ModelLewis Model

even more general than Bronsted-even more general than Bronsted-Lowry Lowry

acidacid electron pair ____________electron pair ____________ has empty atomic orbitalshas empty atomic orbitals

basebase electron pair ____________electron pair ____________ has lone pairhas lone pair

ExamplesExamples

AlAl3+3+ + 6H + 6H22O O [Al(H [Al(H22O)O)66]]3+3+

SOSO33 + H + H22O O H H22SOSO44

Documents

Ch. 14: Acids and Bases 14.1 Intro to Acids and Bases 14.2 Acid Strength 14.3 pH Scale