Acidsbase2

Chapter
“Acids, Bases,
and Salts”

Section 1Section 1
Acid-Base TheoriesAcid-Base Theories
OBJECTIVES:OBJECTIVES:
–Define the properties of
acids and bases.

Section 19.1Section 19.1
–Compare and contrast
acids and bases as defined
by the theories of:
a) Arrhenius,
b) Brønsted-Lowry, and
c) Lewis.

Properties of AcidsProperties of Acids
They tasteThey taste soursour (don’t try this at home).(don’t try this at home).
They canThey can conduct electricityconduct electricity..
–Can be strong or weak electrolytes in
aqueous solution
React with metalsReact with metals to form Hto form H22 gas.gas.
Change the colorChange the color of indicatorsof indicators
(for example: blue litmus turns to red).(for example: blue litmus turns to red).
React with basesReact with bases (metallic hydroxides)(metallic hydroxides)
to form water and a salt.to form water and a salt.

Properties of AcidsProperties of Acids
They have aThey have a pH of less than 7pH of less than 7 (more(more
on this concept of pH in a later lesson)on this concept of pH in a later lesson)
TheyThey react with carbonates andreact with carbonates and
bicarbonatesbicarbonates to produce a salt, water,to produce a salt, water,
and carbon dioxide gasand carbon dioxide gas
How do you know if a chemical is anHow do you know if a chemical is an
acid?acid?
– It usually starts with Hydrogen.
– HCl, H2SO4, HNO3, etc. (but not water!)

Acids Affect Indicators, byAcids Affect Indicators, by
changing their colorchanging their color
Blue litmus paper turns red in
contact with an acid (and red paper
stays red).

AcidsAcids
have ahave a
pHpH
lessless
than 7than 7

Acids React with Active MetalsAcids React with Active Metals
Acids react with active metals to
form salts and hydrogen gas:
HCl(aq) + Mg(s) → MgCl2(aq) + H2(g)
This is a single-replacement reaction

Acids React with CarbonatesAcids React with Carbonates
and Bicarbonatesand Bicarbonates
HCl + NaHCO3
NaCl + H2O + CO2
Hydrochloric acid + sodium bicarbonate
salt + water + carbon dioxide
An old-time home remedy for
relieving an upset stomach

Effects ofEffects of Acid RainAcid Rain on Marbleon Marble
(marble is calcium(marble is calcium carbonatecarbonate))
George Washington:
BEFORE acid rain
George Washington:
AFTER acid rain

AcidsAcids NeutralizeNeutralize BasesBases
HCl + NaOH → NaCl + H2O
-Neutralization reactions
ALWAYS produce a salt (which is
an ionic compound) and water.
-Of course, it takes the right
proportion of acid and base to
produce a neutral salt

Sulfuric AcidSulfuric Acid = H= H22SOSO44
Highest volumeHighest volume
production ofproduction of anyany
chemical in the U.S.chemical in the U.S.
(approximately 60 billion pounds/year)(approximately 60 billion pounds/year)
Used in the productionUsed in the production
of paperof paper
Used in production ofUsed in production of
fertilizersfertilizers
Used in petroleumUsed in petroleum
refining; auto batteriesrefining; auto batteries

Nitric AcidNitric Acid = HNO= HNO33
of fertilizersof fertilizers
of explosivesof explosives
Nitric acid is aNitric acid is a volatilevolatile
acid – its reactiveacid – its reactive
components evaporatecomponents evaporate
easilyeasily
Stains proteins yellowStains proteins yellow
(including skin!)(including skin!)

Hydrochloric AcidHydrochloric Acid = HCl= HCl
Used in the “pickling”Used in the “pickling”
of steelof steel
Used to purifyUsed to purify
magnesium from seamagnesium from sea
waterwater
Part of gastric juice, itPart of gastric juice, it
aids in the digestion ofaids in the digestion of
proteinsproteins
Sold commercially asSold commercially as
Muriatic acidMuriatic acid

Phosphoric AcidPhosphoric Acid = H= H33POPO44
A flavoring agent inA flavoring agent in
sodas (adds “tart”)sodas (adds “tart”)
Used in theUsed in the
manufacture ofmanufacture of
detergentsdetergents
manufacture ofmanufacture of
fertilizersfertilizers
NotNot a commona common
laboratory reagentlaboratory reagent

Acetic AcidAcetic Acid = HC= HC22HH33OO22
(also called Ethanoic Acid, CH(also called Ethanoic Acid, CH33COOH)COOH)
manufacture of plasticsmanufacture of plastics
Used in makingUsed in making
pharmaceuticalspharmaceuticals
Acetic acid is the acidAcetic acid is the acid
that is present inthat is present in
householdhousehold vinegarvinegar

Properties of BasesProperties of Bases (metallic hydroxides)(metallic hydroxides)
React with acidsReact with acids to form waterto form water
and a salt.and a salt.
TasteTaste bitterbitter..
Feel slipperyFeel slippery (don’t try this either).(don’t try this either).
Can be strong or weakCan be strong or weak
electrolyteselectrolytes in aqueous solutionin aqueous solution
Change the colorChange the color of indicatorsof indicators
(red litmus turns blue).(red litmus turns blue).

Examples of BasesExamples of Bases
(metallic hydroxides)(metallic hydroxides)
 Sodium hydroxide,Sodium hydroxide, NaOHNaOH
((lye for drain cleaner; soaplye for drain cleaner; soap))
 Potassium hydroxide,Potassium hydroxide,
KOHKOH ((alkaline batteriesalkaline batteries))
 Magnesium hydroxide,Magnesium hydroxide,
Mg(OH)Mg(OH)22 ((Milk of MagnesiaMilk of Magnesia))
 Calcium hydroxide,Calcium hydroxide,
Ca(OH)Ca(OH)22 ((limelime;; masonrymasonry))

Bases Affect IndicatorsBases Affect Indicators
Red litmus paper
turns blue in contact
with a base (and blue
paper stays blue).
Phenolphthalein
turns purple in a
base.

BasesBases
have ahave a
pHpH
greatergreater
than 7than 7

Bases Neutralize AcidsBases Neutralize Acids
Milk of Magnesia contains
magnesium hydroxide,
Mg(OH)2, which neutralizes
stomach acid, HCl.
2 HCl + Mg(OH)2
MgCl2 + 2 H2O
Magnesium salts can cause
diarrhea (thus they are used
as a laxative) and may also
cause kidney stones.

Svante ArrheniusSvante Arrhenius
He was a Swedish chemist (1859-He was a Swedish chemist (1859-
1927), and a Nobel prize winner in1927), and a Nobel prize winner in
chemistry (1903)chemistry (1903)
one of the first chemists to explainone of the first chemists to explain
the chemical theory of the behaviorthe chemical theory of the behavior
of acids and basesof acids and bases
Dr. Hubert Alyea (professor emeritusDr. Hubert Alyea (professor emeritus
at Princeton University) was the lastat Princeton University) was the last
graduate student of Arrhenius.graduate student of Arrhenius.

Hubert N. Alyea (1903-1996)Hubert N. Alyea (1903-1996)

1. Arrhenius Definition - 18871. Arrhenius Definition - 1887
AcidsAcids produce hydrogen ions (Hproduce hydrogen ions (H1+1+
))
inin aqueous solutionaqueous solution (HCl(HCl →→ HH1+1+
+ Cl+ Cl1-1-
))
BasesBases produce hydroxide ionsproduce hydroxide ions
(OH(OH1-1-
) when dissolved) when dissolved in waterin water..
(NaOH → Na1+
+ OH1-
)
Limited toLimited to aqueous solutionsaqueous solutions..
Only one kind of base (hydroxides)Only one kind of base (hydroxides)
NHNH33 (ammonia) could not be an(ammonia) could not be an
Arrhenius base: no OHArrhenius base: no OH1-1-
produced.produced.

Svante Arrhenius (1859-1927)Svante Arrhenius (1859-1927)

Polyprotic Acids?Polyprotic Acids?
Some compounds haveSome compounds have more thanmore than
one ionizable hydrogenone ionizable hydrogen to releaseto release
HNOHNO33 nitric acid -nitric acid - monomonoproticprotic
HH22SOSO44 sulfuric acid -sulfuric acid - didiprotic - 2 Hprotic - 2 H++
HH33POPO44 phosphoric acid -phosphoric acid - tritriprotic - 3protic - 3
HH++
Having more than one ionizableHaving more than one ionizable
hydrogen doeshydrogen does notnot mean stronger!mean stronger!

AcidsAcids
Not all compounds that haveNot all compounds that have
hydrogen are acids. Water?hydrogen are acids. Water?
Also, not all the hydrogen in anAlso, not all the hydrogen in an
acid may be released as ionsacid may be released as ions
–only those that have very polar
bonds are ionizable - this is
when the hydrogen is joined to
a very electronegative element

Arrhenius examples...Arrhenius examples...
Consider HCl = it is an acid!Consider HCl = it is an acid!
What about CHWhat about CH44 (methane)?(methane)?
CHCH33COOH (ethanoic acid, alsoCOOH (ethanoic acid, also
called acetic acid) - it has 4called acetic acid) - it has 4
hydrogens just like methanehydrogens just like methane
does…?does…?
Table 19.2, p. 589 for bases,Table 19.2, p. 589 for bases,
which are metallic hydroxideswhich are metallic hydroxides

Organic AcidsOrganic Acids (those with carbon)(those with carbon)
Organic acids all contain the carboxyl group,
(-COOH), sometimes several of them.
CH3COOH – of the 4 hydrogen, only 1 ionizable
The carboxyl group is a poor proton donor, so
ALL organic acids are weak acids.
(due to being bonded to the highly electronegative Oxygen)

2. Brønsted-Lowry - 19232. Brønsted-Lowry - 1923
A broader definition than ArrheniusA broader definition than Arrhenius
AcidAcid is hydrogen-ion donor (His hydrogen-ion donor (H++
oror
proton);proton); basebase is hydrogen-ion acceptor.is hydrogen-ion 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 it’s
proton to water.
HClHCl(g)(g) + H+ H22OO(l)(l) ↔↔ HH33OO++
(aq)(aq) + Cl+ Cl--
(aq)(aq)
Water is a base; makes hydronium ion.Water is a base; makes hydronium ion.

Johannes Brønsted Thomas LowryJohannes Brønsted Thomas Lowry
(1879-1947) (1874-1936)(1879-1947) (1874-1936)
DenmarkDenmark EnglandEngland

Why Ammonia is a BaseWhy Ammonia is a Base
Ammonia can be explained as aAmmonia can be explained as a
base by using Brønsted-Lowry:base by using Brønsted-Lowry:
NHNH3(aq)3(aq) + H+ H22OO(l)(l) ↔ NH↔ NH44
1+1+
(aq)(aq) + OH+ OH1-1-
(aq)(aq)
Ammonia is the hydrogen ionAmmonia is the hydrogen ion
acceptor (acceptor (basebase), and water is the), and water is the
hydrogen ion donor (hydrogen ion donor (acidacid).).
This causes the OHThis causes the OH1-1-
concentration toconcentration to
be greater than in pure water, andbe greater than in pure water, and
the ammonia solution isthe ammonia solution is basicbasic

Acids and bases come inAcids and bases come in
pairspairsA “A “conjugate baseconjugate base”” is the remainder ofis the remainder of
the original acid, after itthe original acid, after it donatesdonates it’sit’s
hydrogen ionhydrogen ion
A “A “conjugate acidconjugate acid”” is the particleis the particle
formed when the original baseformed when the original base gainsgains aa
hydrogen ionhydrogen ion
Thus, a conjugate acid-base pair is related byThus, a conjugate acid-base pair is related by
thethe loss or gainloss or gain of aof a single hydrogen ionsingle hydrogen ion..
Chemical IndicatorsChemical Indicators?? They are weakThey are weak
acids or bases that have a differentacids or bases that have a different
color from their original acid and basecolor from their original acid and base

Acids and bases come inAcids and bases come in
pairspairsGeneral equation is:General equation is:
HAHA(aq)(aq) + H+ H22OO(l)(l) ↔↔ HH33OO++
(aq)(aq) + A+ A--
(aq)(aq)
Acid + BaseAcid + Base ↔↔ Conjugate acid + Conjugate baseConjugate acid + Conjugate base
NHNH33 + H+ H22OO ↔↔ NHNH44
1+1+
+ OH+ OH1-1-
basebase acidacid c.a. c.b.c.a. c.b.
HCl + HHCl + H22OO ↔↔ HH33OO1+1+
+ Cl+ Cl1-1-
acidacid basebase c.a. c.b.c.a. c.b.
AmphotericAmphoteric – a substance that can– a substance that can act asact as
bothboth an acid and base- as water showsan acid and base- as water shows

3. Lewis Acids and Bases3. Lewis Acids and Bases
Gilbert Lewis focused on theGilbert Lewis focused on the
donation or acceptance of a pair ofdonation or acceptance of a pair of
electrons during a reactionelectrons during a reaction
Lewis AcidLewis Acid - electron pair acceptor- electron pair acceptor
Lewis BaseLewis Base - electron pair donor- electron pair donor
Most general of all 3 definitions;Most general of all 3 definitions;
acids don’t even need hydrogen!acids don’t even need hydrogen!
SummarySummary: Table 19.4, page 592: Table 19.4, page 592

Gilbert Lewis (1875-1946)Gilbert Lewis (1875-1946)

Hydrogen Ions and AcidityHydrogen Ions and Acidity
–Describe how [H1+
] and
[OH1-
] are related in an
aqueous solution.

Section 2Section 2
–Classify a solution as
neutral, acidic, or basic
given the hydrogen-ion
or hydroxide-ion
concentration.

–Convert hydrogen-ion
concentrations into pH
values and hydroxide-ion
concentrations into pOH
values.

–Describe the purpose of
an acid-base indicator.

Hydrogen Ions from WaterHydrogen Ions from Water
Water ionizes, or falls apart into ions:Water ionizes, or falls apart into ions:
H2O ↔ H1+
+ OH1-
Called the “Called the “self ionizationself ionization” of water” of water
Occurs to aOccurs to a very smallvery small extentextent::
[H1+
] = [OH1-
] = 1 x 10-7
M
Since they are equal, aSince they are equal, a neutralneutral solutionsolution
results from waterresults from water
KKww = [H= [H1+1+
] x [OH] x [OH1-1-
] = 1 x 10] = 1 x 10-14-14
MM22
KKww is called the “is called the “ion product constantion product constant” for water” for water

Ion Product ConstantIon Product Constant
HH22OO ↔↔ HH1+1+
+ OH+ OH1-1-
KKww isis constantconstant in every aqueous solution:in every aqueous solution:
[H[H++
] x [OH] x [OH--
] =] = 1 x 101 x 10-14-14
MM22
If [HIf [H++
] > 10] > 10-7-7
then [OHthen [OH--
] < 10] < 10-7-7
If [HIf [H++
] < 10] < 10-7-7
then [OHthen [OH--
] > 10] > 10-7-7
If we know one, other can be determinedIf we know one, other can be determined
If [HIf [H++
] > 10] > 10-7-7
, it is, it is acidicacidic and [OHand [OH--
] < 10] < 10-7-7
If [HIf [H++
] < 10] < 10-7-7
, it is, it is basicbasic and [OHand [OH--
] > 10] > 10-7-7

The pH concept – from 0 to 14The pH concept – from 0 to 14
pH =pH = pouvoir hydrogenepouvoir hydrogene (Fr.)(Fr.)
“hydrogen power”“hydrogen power”
definition:definition: pH = -log[HpH = -log[H++
]]
inin neutralneutral pH = -log(1 x 10pH = -log(1 x 10-7-7
)) = 7= 7
inin acidicacidic solution [Hsolution [H++
] > 10] > 10-7-7
pHpH << -log(10-log(10-7-7
))
– pH < 7 (from 0 to 7 is the acid range)
– in base, pH > 7 (7 to 14 is base range)

Calculating pOHCalculating pOH
pOH = -log [OHpOH = -log [OH--
]]
[H[H++
] x [OH] x [OH--
] = 1 x 10] = 1 x 10-14-14
MM22
pH + pOH = 14pH + pOH = 14
Thus, a solution with a pOHThus, a solution with a pOH
less than 7 is basic; with aless than 7 is basic; with a
pOH greater than 7 is an acidpOH greater than 7 is an acid
Not greatly used like pH is.Not greatly used like pH is.

pH and Significant FigurespH and Significant Figures
For pH calculations, the hydrogenFor pH calculations, the hydrogen
ion concentration is usuallyion concentration is usually
expressed in scientific notationexpressed in scientific notation
[H[H1+1+
] = 0.0010 M = 1.0 x 10] = 0.0010 M = 1.0 x 10-3-3
M, andM, and
0.000.001010 has 2 significant figureshas 2 significant figures
the pH = 3.the pH = 3.0000, with the two, with the two
numbers to the right of the decimalnumbers to the right of the decimal
corresponding to the two significantcorresponding to the two significant
figuresfigures

Measuring pHMeasuring pH
Why measure pH?Why measure pH?
Everyday solutions
we use - everything
from swimming pools,
soil conditions for
plants, medical
diagnosis, soaps and
shampoos, etc.
Sometimes we can useSometimes we can use
indicatorsindicators, other times, other times
we might need awe might need a pHpH
metermeter

How to measure pH with wide-range paperHow to measure pH with wide-range paper
1. Moisten the pH
indicator paper strip
with a few drops of
solution, by using a
stirring rod.
2.Compare the color
to the chart on the vial
– then read the pH
value.

Some of theSome of the
many pHmany pH
IndicatorsIndicators
and theirand their
pH rangepH range

Acid-Base IndicatorsAcid-Base Indicators
Although useful, there areAlthough useful, there are limitationslimitations
to indicators:to indicators:
–usually given for a certain
temperature (25 o
C), thus may
change at different temperatures
–what if the solution already has a
color, like paint?
– the ability of the human eye to
distinguish colors is limited

Acid-Base IndicatorsAcid-Base Indicators
AA pH meterpH meter may give more definitivemay give more definitive
resultsresults
–some are large, others portable
–works by measuring the voltage
between two electrodes; typically
accurate to within 0.01 pH unit of
the true pH
–Instruments need to be calibrated
–Fig. 19.15, p.603

Section 3Section 3
Strengths of Acids and BasesStrengths of Acids and Bases
–Define strong acids and
weak acids.

Section 3Section 3
–Describe how an acid’s
strength is related to the
value of its acid
dissociation constant.

Section 3Section 3
–Calculate an acid
dissociation constant (Ka)
from concentration and
pH measurements.

Section 3Section 3
–Order acids by strength
according to their acid
dissociation constants
(Ka).

Section 3Section 3
–Order bases by strength
according to their base
dissociation constants
(Kb).

StrengthStrength
Acids and Bases are classified acordingAcids and Bases are classified acording
to the degree to which they ionize into the degree to which they ionize in
water:water:
–Strong are completely ionized in
aqueous solution; this means they
ionize 100 %
–Weak ionize only slightly in aqueous
solution
StrengthStrength is very different fromis very different from
ConcentrationConcentration

StrengthStrength
Strong – means it formsStrong – means it forms manymany
ions when dissolved (100 %ions when dissolved (100 %
ionization)ionization)
Mg(OH)Mg(OH)22 is a strong base- it fallsis a strong base- it falls
completely apart (nearly 100%completely apart (nearly 100%
when dissolved).when dissolved).
–But, not much dissolves- so it
is not concentrated

Strong Acid DissociationStrong Acid Dissociation
(makes 100 % ions)(makes 100 % ions)

Weak Acid DissociationWeak Acid Dissociation
(only partially ionizes)(only partially ionizes)

Measuring strengthMeasuring strength
Ionization is reversible:Ionization is reversible:
HA + HHA + H22OO ↔↔ HH++
+ A+ A--
This makes an equilibriumThis makes an equilibrium
Acid dissociation constant = KAcid dissociation constant = Kaa
KKaa = [H= [H++
][A][A--
]]
[HA][HA]
Stronger acidStronger acid = more products (ions),= more products (ions),
thus athus a larger Klarger Kaa (Table 19.7, page 607)(Table 19.7, page 607)
(Note that water is NOT shown,
because its concentration is
constant, and built into Ka)
(Note that the arrow
goes both directions.)

What about bases?What about bases?
Strong bases dissociate completely.Strong bases dissociate completely.
MOH + HMOH + H22OO ↔↔ MM++
+ OH+ OH--
(M = a metal)(M = a metal)
Base dissociation constant = KBase dissociation constant = Kbb
KKbb = [M= [M++
][OH][OH--
]]
[MOH][MOH]
Stronger baseStronger base = more dissociated= more dissociated
ions are produced, thus aions are produced, thus a larger Klarger Kbb..

Strength vs. ConcentrationStrength vs. Concentration
The wordsThe words concentratedconcentrated andand dilutedilute telltell
how much of an acid or base ishow much of an acid or base is
dissolved in solution - refers to thedissolved in solution - refers to the
number of moles of acid or base in anumber of moles of acid or base in a
given volumegiven volume
The wordsThe words strongstrong andand weakweak refer to therefer to the
extent of ionization of an acid or baseextent of ionization of an acid or base
Is aIs a concentrated, weakconcentrated, weak acid possible?acid possible?

PracticePractice
Write the KWrite the Kaa expression for HNOexpression for HNO22
1) Equation: HNO2 ↔ H1+
+ NO2
1-
2) Ka = [H1+
] x [NO2
1-
]
[HNO2]
Write the KWrite the Kbb expression for NHexpression for NH33
(as NH(as NH44OH)OH)

Section 4Section 4
Neutralization ReactionsNeutralization Reactions
–Define the products of
an acid-base reaction.

Section 4Section 4
–Explain how acid-base
titration is used to
calculate the
concentration of an acid
or a base.

Section 4Section 4
–Explain the concept of
equivalence in
neutralization reactions.

Section 4Section 4
–Describe the relationship
between equivalence
point and the end point
of a titration.

Acid-Base ReactionsAcid-Base Reactions
Acid + BaseAcid + Base  Water +Water +
SaltSalt
Properties related to every day:Properties related to every day:
–antacids depend on neutralization
–farmers adjust the soil pH
–formation of cave stalactites
–human body kidney stones from
insoluble salts

Acid-Base ReactionsAcid-Base Reactions
Neutralization ReactionNeutralization Reaction - a reaction- a reaction
in which an acid and a base react inin which an acid and a base react in
an aqueous solution to produce aan aqueous solution to produce a
salt and water:salt and water:
HClHCl(aq)(aq) + NaOH+ NaOH(aq)(aq)  NaClNaCl(aq)(aq) + H+ H22OO(l)(l)
HH22SOSO4(aq)4(aq) + 2KOH+ 2KOH(aq)(aq)  KK22SOSO4(aq)4(aq) + 2H+ 2H22OO(l)(l)
–Table 19.9, page 613 lists some salts

TitrationTitration
TitrationTitration is the process of adding ais the process of adding a
known amount of solution of knownknown amount of solution of known
concentration to determine theconcentration to determine the
concentration of another solutionconcentration of another solution
Remember? - aRemember? - a balanced equationbalanced equation isis
aa mole ratiomole ratio
TheThe equivalence pointequivalence point is when the molesis when the moles
of hydrogen ions isof hydrogen ions is equalequal to the molesto the moles
of hydroxide ions (= neutralized!)of hydroxide ions (= neutralized!)

TitrationTitration
The concentration of acid (or base)The concentration of acid (or base)
in solution can be determined byin solution can be determined by
performing a neutralization reactionperforming a neutralization reaction
–An indicator is used to show
when neutralization has occurred
–Often we use phenolphthalein-
because it is colorless in neutral
and acid; turns pink in base

Steps - Neutralization reactionSteps - Neutralization reaction
#1. A measured volume of acid of#1. A measured volume of acid of
unknown concentration is added tounknown concentration is added to
a flaska flask
#2. Several drops of indicator added#2. Several drops of indicator added
#3. A base of known concentration is#3. A base of known concentration is
slowly added, until the indicatorslowly added, until the indicator
changes color; measure thechanges color; measure the
volumevolume
–Figure 19.22, page 615

NeutralizationNeutralization
The solution of knownThe solution of known
concentration is called theconcentration is called the
standard solutionstandard solution
–added by using a buret
Continue adding until theContinue adding until the indicatorindicator
changes colorchanges color
–called the “end point” of the titration
–Sample Problem 19.7, page 616

Section 5Section 5
Salts in SolutionSalts in Solution
–Describe when a
solution of a salt is acidic
or basic.

Section 5Section 5
Salts in SolutionSalts in Solution
–Demonstrate with
equations how buffers
resist changes in pH.

Salt HydrolysisSalt Hydrolysis
AA saltsalt is an ionic compound that:is an ionic compound that:
–comes from the anion of an acid
–comes from the cation of a base
–is formed from a neutralization
reaction
–some neutral; others acidic or basic
““Salt hydrolysisSalt hydrolysis”” - a- a saltsalt that reactsthat reacts
with water to produce an acid or basewith water to produce an acid or base

Hydrolyzing salts usually come from:Hydrolyzing salts usually come from:
1. a strong acid + a weak base, or
2. a weak acid + a strong base
Strong refers to theStrong refers to the degree ofdegree of
ionizationionization
A strong Acid + a strong Base = Neutral Salt
How do youHow do you knowknow if it’s strong?if it’s strong?
– Refer to the handout provided
(downloadable from my web site)

To see if the resulting salt isTo see if the resulting salt is
acidic or basic, check theacidic or basic, check the
“parent” acid and base“parent” acid and base thatthat
formed it. Practice on these:formed it. Practice on these:
HCl + NaOH
H2SO4 + NH4OH
CH3COOH + KOH
NaCl, a neutral salt
(NH4)2SO4, acidic salt
CH3COOK, basic salt

BuffersBuffers
BuffersBuffers are solutions in which theare solutions in which the
pH remains relatively constant,pH remains relatively constant,
even when small amounts of acideven when small amounts of acid
or base are addedor base are added
–made from a pair of chemicals:
a weak acid and one of it’s
salts; or a weak base and one
of it’s salts

BuffersBuffers
A buffer system is better able toA buffer system is better able to
resist changes in pH than pure waterresist changes in pH than pure water
Since it is aSince it is a pairpair of chemicals:of chemicals:
–one chemical neutralizes any acid
added, while the other chemical
would neutralize any additional
base
–AND, they produce each other
in the process!!!

BuffersBuffers
Example: Ethanoic (acetic) acidExample: Ethanoic (acetic) acid
and sodium ethanoate (alsoand sodium ethanoate (also
called sodium acetate)called sodium acetate)
Examples on page 621 of theseExamples on page 621 of these
TheThe buffer capacitybuffer capacity is theis the
amount of acid or base that canamount of acid or base that can
be added before a significantbe added before a significant
change in pHchange in pH

BuffersBuffers
The two buffers that are crucial toThe two buffers that are crucial to
maintain the pH of human blood are:maintain the pH of human blood are:
1. carbonic acid (H2CO3) & hydrogen
carbonate (HCO3
1-
)
2. dihydrogen phosphate (H2PO4
1-
) &
monohydrogen phoshate (HPO4
2-
)
–Table 19.10, page 621 has some
important buffer systems
–Conceptual Problem 19.2, p. 622

Aspirin (which
is a type of
acid)
sometimes
causes
stomach
upset; thus by
adding a
“buffer”, it
does not
cause the
acid irritation.
Bufferin is
one brand of
a buffered
aspirin that
is sold in
stores.
What about
the cost
compared to
plain
aspirin?

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