BackBack

Bires, 2010

Chapter 15-16Chapter 15-16

pHpHAcids and BasesAcids and Bases

Acids and Bases are all around us.Acids and Bases are all around us.

Our very existence relies upon the Our very existence relies upon the interactions of acidic and basic interactions of acidic and basic

substances.substances.

Pages 452-507

Burettes are used in titrations, page 498

In neutral water, there is a balance of equal concentrations of H3O+ and OH-. (1x10-7M of each)

Bires, 2010

BackBack

Slide 2

Properties of AcidsProperties of Acids AcidsAcids…… Taste sour (but don't taste them in lab!!) Taste sour (but don't taste them in lab!!) Form ElectrolytesForm Electrolytes React with bases to form salts and water. React with bases to form salts and water. Turn Turn Blue Litmus PaperBlue Litmus Paper to to RedRed React with metals, dissolving the metal atoms React with metals, dissolving the metal atoms

into ions, and releasing Hinto ions, and releasing H22 gas. gas.

Hydronium ion ( (HH33OO++) is the “acid ion”) is the “acid ion”

Aqueous Acids (strong and weak).mov

)()(32)( aqaqaq ClOHOHHCl

)(2)(2)( aqgaq ZnClHZnHCl

Bires, 2010

BackBack

Slide 3

Properties of BasesProperties of Bases BasesBases…… Feel slipperyFeel slippery Taste bitter (but don't taste them in lab!!) Taste bitter (but don't taste them in lab!!) Form electrolytesForm electrolytes React with acids to form salts and water React with acids to form salts and water Turn Turn Red Litmus PaperRed Litmus Paper to to BlueBlue Greater threat to Greater threat to biological material due to their due to their

hydrophilichydrophilic nature. nature. Hydroxide ( (OHOH--) “base ion”) “base ion”

Aqueous Bases (strong and weak).mov

)()()( aqaqaq OHNaNaOH

Bires, 2010

BackBack

Slide 4

Some examples of acids and basesSome examples of acids and bases HNO3 – can give up one Hcan give up one H++ to make H to make H33OO++

acidacid NaOH – will deposit the OH – will deposit the OH-- ion ion

basebase

HCl – can give up one H – can give up one H++ to form a Cl to form a Cl-- and H and H33OO++

ions.ions. acidacid

On your own, predict if each of the following is an acid or a base:

HIO4, HClO4, Ba(OH)2, H3PO4, Na3PO4..

Bires, 2010

BackBack

Slide 5

Strong AcidsStrong Acids Strong acids have a Strong acids have a very electronegative endvery electronegative end

opposite from the Hopposite from the H++ end. end. The more The more polarpolar an acid, the stronger it will be. an acid, the stronger it will be.

Strong acidsStrong acids dissociatedissociate completely completely

Diprotic, Triprotic, Polyprotic AcidsDiprotic, Triprotic, Polyprotic Acids can can give up more than one Hgive up more than one H++

HH22SOSO44 is a strong acid. is a strong acid. Why?Why?

HClOHClO44 is one of the strongest acids we can use is one of the strongest acids we can use Why?Why?

Bires, 2010

BackBack

Slide 6

Strong BasesStrong Bases Strong basesStrong bases

dissociate completelydissociate completely (dumping OH(dumping OH--)).. Weak basesWeak bases

take Htake H++ to leave OH to leave OH-- behind. behind.

Ca(OH)Ca(OH)22 is a strong base. is a strong base. Why?Why?

KK22COCO33 is a weak base.is a weak base. Why?Why?

Ammonia, Ammonia, NHNH33 is a weak base. is a weak base. How?How?

Bires, 2010

BackBack

Slide 7

Three ways to describe acids/basesThree ways to describe acids/bases Arrhenius Model of Acids and Bases: of Acids and Bases:

Acids shift a water solution toward HAcids shift a water solution toward H++ imbalance imbalance Bases remove HBases remove H++ ions from solution, leaving an OH ions from solution, leaving an OH--

imbalanceimbalance..

Bronsted-Lowry Model of Acids and Bases: Acids are proton donorsAcids are proton donors.. Bases are proton acceptorsBases are proton acceptors..

Lewis acid-base model:: Acid = e- pair acceptor Base = e- pair donor

Acid-Base reactions produce pairs of molecules, Acid-Base reactions produce pairs of molecules, known as known as conjugate pairsconjugate pairs..

Bires, 2010

BackBack

Slide 8

Conjugate Acid - Base PairsConjugate Acid - Base PairsAcidsAcids conjugate basesconjugate bases. How?. How?

BasesBases conjugate acidsconjugate acids. . How?How?

3323 NOOHOHHNOConjugate

AcidBaseAcid Conjugate

Base

Bires, 2010

BackBack

Slide 9

Identify Conjugate pairs:Identify Conjugate pairs:

KClOHKOHHCl 2

OHPOHPOHOH 342432Acid

Acid

Base

Base Conjugate Acid

Conjugate Base

Conjugate Base

Conjugate Acid

Bires, 2010

BackBack

Slide 10

Strong vs WeakStrong vs Weak Strong Strong AcidAcid / / BaseBase: : dissociate completely.. Dissociation constant, K:

Numerical constant represents Numerical constant represents acid and base strength.acid and base strength. Large K = stronger acid/baseLarge K = stronger acid/base Small K = weaker acid/baseSmall K = weaker acid/base

Acid strength: Acid strength: KKaa

Base strength: Base strength: KKbb

To calculate To calculate KKaa oror KKbb, we use the , we use the concentrations of products divided by reactants at at equilibrium..

Bires, 2010

BackBack

Slide 12

The pH scaleThe pH scale The “The “pp” = “” = “negative log” (” (-log)) The “The “HH” = ” = hydronium ionhydronium ion [H [H33OO++] concentration.] concentration.

pH = pH = negative log of the hydronium ion concentration -log [H-log [H33OO++]]

Low pHLow pH high Hhigh H33O+O+ concentrationconcentration. “. “AcidsAcids””

High pHHigh pH low Hlow H33OO++ concentrationconcentration. “. “BasesBases””

When a solution When a solution increases in pHincreases in pH, does it , does it become become more acidicmore acidic, or , or more basicmore basic??

Bires, 2010

BackBack

Slide 13

The pH scaleThe pH scale Low pHLow pH high Hhigh H33OO++ concentration concentration. “. “AcidsAcids””

High pHHigh pH low Hlow H33OO++ concentration concentration. “. “BasesBases””

Bires, 2010

BackBack

Slide 14

pH calculations:pH calculations: Try These:Try These:

1.1. What is the pH of a solution whose [HWhat is the pH of a solution whose [H33OO++] is 1 ] is 1

x 10x 10-5-5 M? M?

2.2. What is the [HWhat is the [H33OO++] concentration of a solution ] concentration of a solution

with a pH of 9? with a pH of 9?

3.3. What is the pH of a solution with a [HWhat is the pH of a solution with a [H33OO++] ]

concentration of 1.0 x 10concentration of 1.0 x 10-12-12 M? M?

4.4. What is the pH of a solution whose [HWhat is the pH of a solution whose [H33OO++] ]

concentration is 3.0 x 10concentration is 3.0 x 10-3-3 M? M?

5.5. What is the [HWhat is the [H33OO++] concentration of a solution ] concentration of a solution

whose pH is 6.5? whose pH is 6.5?

5

1x10-9 M

2.5

12

3.2x10-7 M

“p” = -logarithm

Bires, 2010

BackBack

Slide 16

HH33OO++ and OH and OH-- In pure water:In pure water:

Perfect balance of HPerfect balance of H33OO++ and OH and OH--..

[H[H33OO++]] = = 1010-7 -7 MM and and [OH[OH--]] = = 1010-7 -7 MM

Acids and Bases:Acids and Bases: Shift balance towards Shift balance towards [H[H33OO++]] or or [OH[OH--]]

KKww:: Autoionization of water.Autoionization of water. = = [H[H33OO++]] x x [OH[OH--]] =1x10=1x10-14-14

pHpH + + pOHpOH = 14 = 14

Amphoteric:

Substances that can act as an acid or base

Bires, 2010

BackBack

Slide 17

Sample HSample H33OO++ and OH and OH-- Problems Problems Determine Determine hydroniumhydronium [ [HH33OO++] and ] and hydroxidehydroxide [ [OHOH--] ]

concentrations of the following solutions:concentrations of the following solutions: 1.0 x 101.0 x 10-4-4 M HCl M HCl

1.0 x 101.0 x 10-3-3 M HNO M HNO33

3.0 x 103.0 x 10-2-2 M NaOH M NaOH

1.0 x 101.0 x 10-4-4 M Ca(OH) M Ca(OH)22

MxOH 43 100.1][ MxOH 10100.1][

MxOH 33 100.1][

MxOH 133 103.3][

MxOH 113 100.5][ MxOH 4100.2][

MxOH 2100.3][

MxOH 11100.1][

Bires, 2010

BackBack

Slide 19

NeutralizationNeutralization Strong acidStrong acid + + strong basestrong base waterwater + a salt + a salt

OHNaNOHNaOHHNO 33

33 NaNOHOHOHNaNOH

Acid Base

Water Salt

Ions

Ions

Salt =

cation + anion

Water = HOH HOH = H+, OH-

Bires, 2010

BackBack

Slide 20

IndicatorsIndicators IndicatorsIndicators

Are one chemical in an acid, another in a base.Are one chemical in an acid, another in a base. Appear to Appear to change color when placed in different change color when placed in different

concentrations of acids and basesconcentrations of acids and bases.. Transition intervalTransition interval

the range of pH that they are effective.the range of pH that they are effective. PhenolPhenolphthaleinphthalein

colorless in the presence of an acid and colorless in the presence of an acid and magentamagenta in in the presence of a the presence of a basebase..

UniUniversversal Inal Indidicatorcator displays a displays a spectrumspectrum of colors, depending upon acid of colors, depending upon acid

and base concentration.and base concentration.

Natural Indicators.mov

Bires, 2010

BackBack

Slide 21

TitrationsTitrations TitrationsTitrations analytically determine an acid’s or base’s analytically determine an acid’s or base’s

concentrationconcentration ( (MM).). far more precise than indicators.far more precise than indicators. Titrations are performed by…Titrations are performed by…

Adding a Adding a known amount of a known-concentration known amount of a known-concentration acidacid to an to an unknown baseunknown base or… or…

Adding a Adding a known amount of a known-concentration known amount of a known-concentration basebase to an to an unknown acidunknown acid..

If the acid is diprotic or the base is (OH)If the acid is diprotic or the base is (OH)22……

bbaa VMVM basebaseacidacid VMVM or

M=molarity

V=volume

Titrations.mov

Bires, 2010

BackBack

Slide 22

Titration CurvesTitration Curves The The equivalence equivalence

pointpoint is the point is the point at which:at which: mole mole acidacid = =

mole mole basebase

Bires, 2010

BackBack

Slide 24

Acid / Base Buffers, Blood BuffersAcid / Base Buffers, Blood Buffers Buffers Buffers resist changes in pHresist changes in pH..

pairs or sets of compounds, similar to the acid or the base that is being pairs or sets of compounds, similar to the acid or the base that is being buffered.buffered.

When an When an acid is added:acid is added: the buffer the buffer absorbs the extra Habsorbs the extra H++ ion. ion.

When a When a base is added:base is added: the the buffer releases a Hbuffer releases a H++ ion to react with the OH ion to react with the OH-- of the base of the base

and produce Hand produce H22O.O. We have special buffers in our We have special buffers in our blood to stabilize the to stabilize the

pH of our pH of our blood.. protect delicate organ systems from pH imbalances from protect delicate organ systems from pH imbalances from

increased or decreased levels of increased or decreased levels of dissolved gasesdissolved gases and and mineralsminerals in our blood. in our blood.

Our normal blood pH is 7.4Our normal blood pH is 7.4

Bires, 2010

BackBack

Slide 26

Acid Rain and Stream Water pHAcid Rain and Stream Water pH Acid rainAcid rain

SOxSOx and and NOxNOx from air pollution react from air pollution react with water to produce acids.with water to produce acids.

The worst reported case of acid rain The worst reported case of acid rain was in West Virginia, measured at a was in West Virginia, measured at a pH of 1.5pH of 1.5, , slightly weaker than slightly weaker than stomach acidstomach acid..

24222 2 HSOHOHSO 2322 222 HHNOOHNO

Bires, 2010

BackBack

Slide 27

Effects of Acid Rain on structuresEffects of Acid Rain on structures The high acidity dissolves the The high acidity dissolves the calcium calcium

compoundscompounds use in bridges, building mortar, use in bridges, building mortar, pavement, foundations, weakening the material pavement, foundations, weakening the material and putting the and putting the structural integritystructural integrity of the of the buildings at risk.buildings at risk.

Marble and granite used in very old statues is at a greater risk due to the absence of modern compounds used to reduce mineral dissolution.

The thin layers of The thin layers of automotive paintautomotive paint suffer suffer substantial damage from acid rain with only substantial damage from acid rain with only small amount of exposure.small amount of exposure.

24

2)(2)(2)(42)(3 SOCaOHCOSOHCaCO lgaqs

Bires, 2010

BackBack

Slide 28

Effects of Acid Rain on HumansEffects of Acid Rain on Humans Acidic water vapor in the air we breath causes Acidic water vapor in the air we breath causes

inflammation in the lungsinflammation in the lungs and deterioration of and deterioration of lung tissue. In those already at risk for lung tissue. In those already at risk for respiratory disruption, the effect can be fatal.respiratory disruption, the effect can be fatal.

The CDC estimates that strict reductions in acid The CDC estimates that strict reductions in acid rain and treatment under the rain and treatment under the Public Health Acid Rain Program will save the will save the US $50 billion by the year 2010.US $50 billion by the year 2010.

Another effect of acid rain is Another effect of acid rain is reduced visibility - -acidic particles in the air react to produce acidic particles in the air react to produce photochemical smogphotochemical smog – a haze that reflects or – a haze that reflects or blocks light like a strong mist on the horizon.blocks light like a strong mist on the horizon.

Bires, 2010

BackBack

Slide 29

Effects on Forest EcosystemsEffects on Forest Ecosystems The reduced pH of soilsThe reduced pH of soils

dramatically reduces the ability of trees and dramatically reduces the ability of trees and underbrush to grow.underbrush to grow.

As pH decreases in aqueous systemsAs pH decreases in aqueous systems metals and other positive ions are dissolved more metals and other positive ions are dissolved more

readily and bound up in complex molecules.readily and bound up in complex molecules. As the soils grow more As the soils grow more acidicacidic

valuable minerals are dissolved and bound up, , made unavailable to the plants that normally draw made unavailable to the plants that normally draw

the minerals from the soils through their roots.the minerals from the soils through their roots.

Bires, 2010

BackBack

Slide 30

Effects of Acid Rain on Stream waterEffects of Acid Rain on Stream water Acid rain is Acid rain is most devastating to aquatic lifemost devastating to aquatic life.. Some metal ions will not dissolve into ions above a Some metal ions will not dissolve into ions above a

certain pH. For Aluminum, that pH is about 5.0.certain pH. For Aluminum, that pH is about 5.0. When the pH of a lake drops below this pH, Al lying at When the pH of a lake drops below this pH, Al lying at

the bottom of the lake goes into solution as ions.the bottom of the lake goes into solution as ions. When the ion-containing acidic water enters the When the ion-containing acidic water enters the

higher-pH gills, higher-pH gills, the metal ions come out of solution, the metal ions come out of solution, forming a forming a film on the gillsfilm on the gills that that suffocatessuffocates the fish. the fish.

Bires, 2010

BackBack

Slide 31

Reduction of Acid RainReduction of Acid Rain Due to Due to multinational cooperationmultinational cooperation, acid rain is on , acid rain is on

the decline.the decline. Coal-burning power plants and industrial Coal-burning power plants and industrial

manufacturing plants must have installed manufacturing plants must have installed elaborate (and expensive) “elaborate (and expensive) “scrubbersscrubbers” to ” to absorb absorb SOxSOx before it can be released.before it can be released.

Due to Due to costscosts of pollutant-reducing equipment, of pollutant-reducing equipment, developing nations still release large amounts developing nations still release large amounts of of SOxSOx pollutants. pollutants.

Further, basic compounds and acid-base Further, basic compounds and acid-base buffers are being added to main lake waters to buffers are being added to main lake waters to protect aquatic wildlife.protect aquatic wildlife.

For more info: Page 493, or EPA’s Clean Air Program: http://www.epa.gov/airmarkets/acidrain/

Bires, 2010

BackBack

Slide 32

Scrubbers!Scrubbers! We can add limestone, CaCOWe can add limestone, CaCO33 to coal-burning power to coal-burning power

plants to react with plants to react with sulfur compoundssulfur compounds before they are before they are released.released.

)(2)()(3 gss COCaOCaCO

)(3)(2)( sgs CaSOSOCaO

End of chapter 15-16