9 - 1Chemistry for Allied Health: Chapter 10 Acids and Bases Acids & Bases Ionization of Water pH Acid-Base Reactions Salt Solutions BuffersDilutionsTitrations

9 - 1Chemistry for Allied Health: Chapter 10

Acids and BasesAcids and Bases

Acids & BasesAcids & Bases

Ionization of WaterIonization of Water

pHpH

Acid-Base ReactionsAcid-Base Reactions

Salt SolutionsSalt Solutions

BuffersBuffers

DilutionsDilutions

TitrationsTitrations


Remember ElectrolytesRemember Electrolytes

Na+

NaCl

Na+ Cl-

Cl-

C6H12O6

C6H12O6

C6H12O6

IonicIonic CovalentCovalent


AcidsAcids

H+

HC2H3O2

H+C2H3O2

1-

C2H3O21- H+

H-Cl

H+Cl-

Cl-

WeakWeak StrongStrong

Lots of IonsOnly a few Ions


AcidsAcids

AcidAcid = gives hydrogen ions in water

H+

H-Cl

H+Cl-

Cl-

HCl

H+ + Cl-

hydrogen ionhydrogen ion


AcidsAcids

H-Cl + H-O-H

+ Cl-

hydronium ionhydronium ion

HO

H

H+

HO

H

H+

Cl-

H-ClH-Cl

AcidAcid = gives hydrogen ions in water


CommonCommon AcidsAcidsBattery Acid Stomach Acid

Coca Cola Carbonated Water

Vinegar Citrus fruitsVitamin CGrapesAspirin

H2SO4

HCl

H3PO4

H2CO3

HC2H3O2

H3C6O7H8

HC6O6H7 H2C4O6H4 H2C9O4H8

Sulfuric AcidHydrochloric Acid

Phosphoric Acid

Carbonic AcidAcetic AcidCitric Acid Ascorbic Acid Tartaric AcidAcetyl Salicylic Acid


H2SO4

HCl

H3PO4

H2CO3

HC2H3O2

H3C6O7H8

HC6O6H7 H2C4O6H4 H2C9O4H8

CommonCommon AcidsAcidsBattery Acid Stomach Acid

Coca Cola Carbonated Water

Vinegar Citrus fruitsVitamin CGrapesAspirin

StrongStrong•100% ionization100% ionization•Strong electrolyteStrong electrolyte

WeakWeak•Partial ionizationPartial ionization•Weak electrolyteWeak electrolyte

•Taste sourTaste sour


AcidsAcidsH-Cl + H-O-H + Cl-

HO

H

H+

HO

H

H+

Cl-

H-ClH-Cl

H+

HC2H3O2

C2H3O21-

HC2H3O2

H-C2H3O2 + H-O-HH

OH

H+ + C2H3O2

-


BaseBase = gives hydroxide ions in water.(Arrhenius definition)

= takes hydrogen ions in water.(Bronsted-Lowry definition)

BasesBases

NaOH

Na+ + OH-OH-

OH-

Na+

Na+

NaOH


Common BasesCommon BasesLye, Drano Potash

Cleaners

Milk of MagnesiaBaking soda Tums /Rolaids Limestone, shellsSoaps Detergents

NaOH KOH

NH3 or NH4OH

Mg(OH)2

NaHCO3

CaCO3

NaC16O2H31 NaC12O4H25S

Sodium HydroxidePotassium Hydroxide

Ammonia

Magnesium HydroxideSodium BicarbonateCalcium Carbonate

Sodium Palmitate Sodium Lauryl

Sulfate


Common BasesCommon BasesLye, Drano Potash

Cleaners

Milk of MagnesiaBaking soda Tums /Rolaids Limestone, shellsSoaps Detergents

NaOH KOH

NH3 or NH4OH

Mg(OH)2

NaHCO3

CaCO3

NaC16O2H31 NaC12O4H25S

StrongStrong•100% ionization100% ionization•Strong electrolyteStrong electrolyte

WeakWeak•Partial ionizationPartial ionization•Weak electrolyteWeak electrolyte

•Taste bitterTaste bitter•Feel SlipperyFeel Slippery


HClO4

H2SO4

HIHBrHCl

HNO3

Perchloric AcidSulfuric AcidHydroIodic AcidHydrobromic AcidHydrochloric AcidNitric Acid

Strong AcidsStrong Acids

LiOHOHNaOH KOH Ca(OHOH)2

Lithium HydroxideSodium HydroxidePotassium HydroxideCalcium Hydroxide

Strong BasesStrong Bases


HNO3 + H2O H3O+ + NO3

-

Water is AmphotericWater is Amphoteric

AcidAciddonates a proton

BaseBasetakes

a proton

NHNH33 + H2O NH4+ + OH-

NHNH33


BaseBasetakes

a proton

HHNONO33


BaseBasetakes

a proton

AcidAcid BaseBase


NH3 + H2O NH4+ + OH- NH3 + H2O NH4+ + OH-


HH22COCO33 + H + H22O HO H33OO++ + + HCOHCO33--

Conjugate Acid - Base PairsConjugate Acid - Base Pairs

conjugate pairconjugate pair

AcidAcid BaseBase AcidAcid BaseBaseconjugate pairconjugate pair


HH22OO


Acid - Acid - BaseBaseHH22COCO33 HHCOCO33

1-1- COCO332-2-

HH33OO++ HOHO1-1-

HH33POPO44HH22POPO44

1-1- POPO443-3-HHPOPO44

2-2-

Acid - Acid - BaseBaseAcid - Acid - BaseBase

Acid - Acid - BaseBaseAcid - Acid - BaseBaseAcid - Acid - BaseBaseAcid - Acid - BaseBase

Acid - Acid - BaseBaseAcid - Acid - BaseBaseAcid - Acid - BaseBaseAcid - Acid - BaseBase Acid - Acid - BaseBase Acid - Acid - BaseBase



AcidAcid BaseBase AcidAcid BaseBase

Dissociation ConstantsDissociation Constants

KKeq = = [ [ HH33OO++ ] [ ] [HCOHCO33--]

[[HH22COCO33 ] [] [HH22O]O]

[[HH22O]O][[HH22O]O]

KKaa== [ [ HH33OO++ ] [ ] [HCOHCO33

--] [[HH22COCO33 ]]

Acid Dissociation ConstantAcid Dissociation Constant



ACIDACID BASEBASE conj acidconj acid conj baseconj base

Dissociation ConstantsDissociation Constants

KKaKKa == [ [ HH33OO++ ] [ ] [HCOHCO33

--] [[HH22COCO33 ]]

ACID Dissociation ConstantACID Dissociation ConstantACID Dissociation ConstantACID Dissociation Constant

Small KSmall Ka a (<1) Weak Acid (<1) Weak Acid [ reactant]>[product][ reactant]>[product]Small KSmall Ka a (<1) Weak Acid (<1) Weak Acid [ reactant]>[product][ reactant]>[product]

= 4.5 x 10= 4.5 x 10-7-7= 4.5 x 10= 4.5 x 10-7-7

Large KLarge Ka a (>1) Strong Acid (>1) Strong Acid [product]>[reactant][product]>[reactant]Large KLarge Ka a (>1) Strong Acid (>1) Strong Acid [product]>[reactant][product]>[reactant]


HH22O O + H + H22O O HOHO-- + + HH33OO++

Ionization of WaterIonization of Water


ACIDACID BASEBASE conj acidconj acidconj baseconj base




Ion product constant of WaterIon product constant of Water


0.000,000,1M0.000,000,1M= 1 x 10= 1 x 10-7-7MM

0.000,000,1M0.000,000,1M= 1 x 10= 1 x 10-7-7MM

Neutral: if [HNeutral: if [H33OO++] = [OH] = [OH--] ]

Acidic: if [HAcidic: if [H33OO++] > [OH] > [OH--] ]

Basic: if [HBasic: if [H33OO++] < [OH] < [OH--] ]



Ion product constant of WaterIon product constant of Water


0.000,000,1M0.000,000,1M= 1 x 10= 1 x 10-7-7MM

0.000,000,1M0.000,000,1M= 1 x 10= 1 x 10-7-7MM

KKww = [H = [H33OO++] [OH] [OH--] = ] = 1 x 101 x 10-14-14KKww = [H = [H33OO++] [OH] [OH--] = ] = 1 x 101 x 10-14-14

[H[H33OO++] [OH] [OH--] = ] = (1 x 10(1 x 10-7-7))(1 x 10(1 x 10-7-7)) = =1 x 101 x 10-14-14[H[H33OO++] [OH] [OH--] = ] = (1 x 10(1 x 10-7-7))(1 x 10(1 x 10-7-7)) = =1 x 101 x 10-14-14


pH pH pH pH

= 1 x 10 -pH pH = pH = - log [H+]

HCl

HC2H3O2

H2O

NaOH

0.000,000,1 M = 1 x 10 -7 M

[H+]

0.000,1 M = 1 x 10 -4 M

0.000,000,000,001 M = 1 x 10 -12 M

100 M = 1 x 10 2 M

77

44

1212

-2-2

990.000,000,001 M 0.000,000,001 M

= 1 x 10 = 1 x 10 -9-9 M MNHNH33

NeutralNeutral

AcidicAcidic

BasicBasic


pHpH pHpH = 1 x 10 -pH pH = pH = - log [H+]

HCl

HC2H3O2

H2O

NaOH

0.000,000,1 M = 1 x 10 -7 M

[H+]

0.000,1 M = 1 x 10 -4 M

0.000,000,000,001 M = 1 x 10 -12 M

100 M = 1 x 10 2 M

77

44

1212

-2-2

990.000,000,001 M 0.000,000,001 M

= 1 x 10 = 1 x 10 -9-9 M MNHNH33

NeutralNeutral

AcidicAcidic

BasicBasic

Citric AcidCitric Acid 0.000,76 M 0.000,76 M = 7.6 x 10 = 7.6 x 10 -4-4 M M


pH pH pH pH

= 1 x 10 -pH pH = pH = - log [H+]pH = pH = - log [H+]

HC2H3O2

[H+]

0.000,1 M = 1 x 10 -4 M 44

3 - 43 - 43 - 43 - 4

Citric AcidCitric Acid

0.001 M = 1 x 10 -3 M

0.000,76 M 0.000,76 M = 7.6 x 10 = 7.6 x 10 -4-4 M M

33

pH = pH = - log (7.6 x 10 -4)pH = pH = - log (7.6 x 10 -4)

= 3.1= 3.1= 3.1= 3.1


pH pH pH pH

[H[H++]] = 1 x 10 = 1 x 10 -pH-pH[H[H++]] = 1 x 10 = 1 x 10 -pH-pH pH = pH = - log [H+]pH = pH = - log [H+]

0.000,000,04 M = 4.0 x 10 4.0 x 10 -8-8 M M

9.39.3

8.58.58.58.5Baking Baking SodaSoda

= 1 x 10 -8.5 M= 3.2 x 10 3.2 x 10 -9-9 M M

pH = pH = - log (4.0 x 10 -8)pH = pH = - log (4.0 x 10 -8)

= 7.4= 7.4= 7.4= 7.4

CleanerCleaner = 1 x 10 -9.4 M= 5.0 x 10 5.0 x 10 -10-10 M M

BloodBlood


pH of somepH of somecommon materialscommon materials

Substance pH

1 M HCl1 M HCl 0.0

Lemon juiceLemon juice 2.3

CoffeeCoffee 5.0

Pure WaterPure Water 7.0

BloodBlood 7.35-7.45

MilkMilk of Magnesia 10.5

1M NaOH1M NaOH 14.0


pH meter:pH meter:

pH paperpH paper::

LitmusLitmus paperpaper::

Pigments:Pigments:Anthocyanins:Anthocyanins:

red cabbagered cabbage, , cranberriescranberries, , rosesroses……Phenolphthalein:Phenolphthalein:Turmeric:Turmeric:


Indicator examplesIndicator examplesAcid-base indicators undergo a color change

at a known pH.

bromthymol blue

phenolphthalein methyl red


AcidAcid--BaseBase Reactions Reactions

HClHCl + + NaOHNaOH

OHOH--

ClCl--

NaNa++

HH++

NaNaClCl + + HHOHOH

AcidAcid BaseBase SaltSalt WaterWater

Neutralization:Neutralization:Strong AcidStrong Acid

++Strong BaseStrong Base



HH22SOSO44 + + KOHKOH

OHOH--

SOSO44-2-2

KK++

HH++

KK22SOSO44 + + HHOHOHAcidAcid BaseBase SaltSalt WaterWater

2222



HCHC22HH33OO22 + + NaHCONaHCO33

HCOHCO331-1-

CC22HH33OO221-1-

NaNa++

HH++

NaNaCC22HH33OO22 + + HH22COCO33

AcidAcid BaseBase

SaltSalt

HH22OO + + COCO2(g)2(g)



Acid Rain on MarbleAcid Rain on Marble

Cream of Tartar & Baking SodaCream of Tartar & Baking Soda

Lemon on FishLemon on Fish


BuffersBuffers

HCHC22HH33OO22 NaCNaC22HH33OO22


Bronsted-Lowry theoryBronsted-Lowry theory

AcidAcid = a Proton donor donates a proton, H+, to solvent

Example: HClHCl

HCl + H2O H3O+ + Cl-

hydronium ion


Example: HNO3

HNO3 + H2O HH33OO++ + NO3-

HNO3 is the acid: it donates the proton.



Base Base == a proton acceptor accepts a Proton, H+, from solvent

NHNH33 + H2O NH4+ + OH-

Accepted H+


NH3 is the Base: it takes the proton.


Hydroxide ions Hydroxide ions (OH-) form when water donates the proton.

NH3 + H2O NH4+ + OH-



In reverse rxn:

gives the HH++ back to HCOHCO33--

In forward rxn:H2CO3 gives the HH++ to H-O-HH-O-H..

HH22COCO33 + + HH22O O HH33OO++ + + HCOHCO33--

ACID ACID 11 BASE BASE 22 ACID ACID 22 BASE BASE 11


HH-O-H +


Polyprotic AcidsPolyprotic Acids

Polyprotic acidsPolyprotic acids = Acids that donate >1 H+:

H2SO4, H2CO3, and H3PO4.


HHPOPO442-2- + H + H22O POO PO44

3-3- + + HH33OO++

HH22POPO44-- + H + H22O O HHPOPO44

2-2- + + HH33OO++

H+’s donate 1 at a time. Example: Phosphoric acid

HH33POPO44 + H + H22O O HH22POPO44-- + + HH33OO++


THE COMMON THE COMMON -IC-IC ACIDS ACIDS

H2SO4 SULFURIC ACID

HNO3 NITRIC ACID

H2CO3 CARBONIC ACID

H3PO4 PHOSPHORIC ACID

HClO3 CHLORIC ACID


EXAMPLE:

HH22SOSO44 (S= +6) Sulfuric acid

HH22SOSO33 (S= +4) Sulfurous acid

HH22SOSO22 (S= +2) hyposulfurous acid


The highest of these four acids is prefixed with a per- (from hyper meaning above).

HClOHClO44 perperchlorchloricic acid acid

HClOHClO33 chloricchloric acid acid

HClOHClO22 chlorouschlorous acid acidHClOHClO hypohypochlorchlorous ous acidacid


Acid SaltsAcid Salts

When an acid has more than one H+ to donate (polyprotic acids), it may form anions with hydrogens still attached.Acid Anions

H2SO4 HSO4- SO4

2-

H2CO3 HCO3- CO3

2-

H3PO4 H2PO4- HPO4

2- PO43-

The anions are still capable of donating these protons, and the salts they form are called acid salts.


These anions are named by indicating the indicating the # of hydrogens left.# of hydrogens left.

HH22PO4- dihydrogendihydrogen phosphate ion

HHPO42- monohydrogenmonohydrogen phosphate

ionHHSO4

- hydrogenhydrogen sulfate

HHSO3- hydrogenhydrogen sulfite

HHCO3- hydrogenhydrogen carbonate


The prefix bi- bi- indicates 1 hydrogen is left from a dihydrogen acid.

HCO3- bicarbonatebicarbonate

HSO3- bisulfitebisulfite


WATERWATER

Water is important for many reasons:

Universal solventUniversal solvent Biological solventBiological solvent Small sizeSmall size Density of water is greater than iceDensity of water is greater than ice Very polarVery polar Hydrogen BondingHydrogen Bonding


Amphoteric SubstancesAmphoteric Substances

Water is amphotericamphoteric : Can act as an acidacid or a or a basebase,

HC2H3O2(aq) + HH22OO(l) HH33OO++ + CC22HH33OO22--((aq)

acid base acid base

HH22OO(l) + NHNH33(aq) NHNH44++

((aq) + OHOH--((aq)

acid base acid baseHERE WATER ACTS AS BOTH AN ACID AND A BASE


The Self-ionization of WaterThe Self-ionization of Water

H2O + H2O H3O+ + OH-

Acid BaseBase


At 25oC, this ionization involves only 1 out of every 550,000,000550,000,000 H2O molecules.

HH22OO(l)(l) + H + H22OO(l)(l) HH33OO++((aq)aq) + + OHOH--

((aqaq) (10-7M) (10-7M)

In 1L H2O, the number of H3O+ and OH- ions formed is 1 x 10-7 moles each.

[ H[ H33OO+ + ]] = 1 x 101 x 10-7 -7 moles/litermoles/liter[ OH[ OH- - ]] = 1 x 10 x 10-7-7 moles/liter moles/liter


In all aqueous solutions, the ion production product for H2O must always be equal to 1.0 x 10equal to 1.0 x 10-14-14

Kw = [ H[ H33OO+ + ]] [ OH[ OH- - ]]

Kw = 1.0 x 101.0 x 10-14-14 at 25 at 25ooCC

Note:Note: [H[H22O]O] is constant and is already included in Kw. (see pg. 260 in text)


If some acid is added to HIf some acid is added to H22OO, causing the [H+] to increase to 0.001 M (1 x 10-3 M), the the [OH[OH--] will decrease to keep Kw = 1 x 10] will decrease to keep Kw = 1 x 10-14-14..

Solving for the new OH- concentration:[H+] x [OH-] = 1 x 101 x 10-14-14

(1 x 10-3) x [OH-] = 1 x 10-14


[OH-][OH-] = = 1 x 101 x 10-11-11 or 0.00000000001M

[OH-][OH-] = 1 x 10-14

1 x 10-3


ProblemProblem: What is the [OH[OH--]] in a solution where [H[H++] is 0.035 M] is 0.035 M ?

Solution:1. Express [H+] in scientific notation.

[H[H++] = 3.5 x 10] = 3.5 x 10-2-2

2. Find [OH-] from Kw.[OH-] = Kw

[H+]


[OH[OH--]] = 1 x 101 x 10-14-14

3.5 x 103.5 x 10-2-2

Answer: [OH[OH--]] = = 2.86 x 102.86 x 10-13-13


pH and pOHpH and pOH

We need to measure and use acids and bases over a very large concentration range.

pH and pOH are systems to keep track of these very large ranges.

pH = -log[HpH = -log[H33OO++]]pOH = -log[OHpOH = -log[OH--]]

pHpH + pOHpOH = 1414


WEDNESDAYWEDNESDAYJANUARY 26, 2000JANUARY 26, 2000

http://terra.chemek.cc.or.us/faculty/mcnm/winter/webpage.htm


The pH ScaleThe pH Scale

Using scientific notation to express [H+] or [OH-] (ex. 3.1 x 103.1 x 10-6-6, 1.0 x 101.0 x 10-7-7, etc.), although simpler than decimal notation, can be cumbersome.

The pH method simplifiespH method simplifies expression of [H+].


pH = -log [HpH = -log [H++] or [H[H++] = 1 x 10] = 1 x 10-pH-pH

pH is the negative of the power which the number 10 must be raise to express the [H+].


Most naturally occurring acids have [H+] much less than 1M.

Orange juiceOrange juice, for example, has [H+] = 2.0 x 10-4 or 0.00020.0002.

Log 2.0 x 10-4 = -3.7

(i.e. 10-3.7 = 2.0 x 10- 4)


Although expressing the concentration in the form of an exponent simplifies it somewhat, the fact that it is almost always a negative number can be a problem.

This is why pHpH is defined as the negativenegative of this exponentexponent. It simply gives us a positivepositive number to work with.


Logarithms are exponents!! Logarithms are exponents!! Log 100 refers to the exponent that the number 10 must be raised to in order to obtain the number 100.

Log 100 = 2 (i.e. 10 2 = 100)Every number has a logarithm.Log 50 = 1.69 (i.e. 10 1.69 = 50)Log 0.0045 = -2.347 (i.e. 10-2.347 = 0.0045)




pOH examplespOH examples

Determine the following: pOH = -log[OH-]

or 14 - pH1. pOH of 1.7x10-4 M NaOH pOH = 3.8 pH = 10.2

2. pOH of 5.2x10-12 M H+

pH = 11.2 pOH = 2.8

3. [OH-] , if the pH is 4.5 pOH = 9.5 [OH-] = 3.2x10-10 M


pH scalepH scale

A log based scale used to keep track of the large change important to acids and bases.

14 7 0

10-14 M 10-7 M 1 MVery Neutral VeryBasic Acidic

When you add an acid, the pH gets smaller.

When you add a base, the pH gets larger.


pH of somepH of somecommon materialscommon materials

Substance pH

1 M HCl1 M HCl 0.0

Lemon juiceLemon juice 2.3

CoffeeCoffee 5.0

Pure WaterPure Water 7.0

BloodBlood 7.35-7.45

MilkMilk of Magnesia 10.5

1M NaOH1M NaOH 14.0


HCl + NaOH NaCl + H2O

NeutralizationNeutralization

The reaction of an acid with a base to produce a salt and water.

We do this when we use antacids.

Neutralization can be used to Determine the amount of acid or base in a sample.

titrationstitrations


Analytical methods based on measurment of volumemeasurment of volume.

• If the concentration of an acid is concentration of an acid is knownknown, the concentration of the base concentration of the base can be found.can be found.

• If we know the concentration of the base, then we can determine the amount of acid.

• All that is needed is some calibrated calibrated glasswareglassware and either an indicatorindicator or pH pH meter.meter.

TITRATIONSTITRATIONS


BuretBuret - volumetric glasware used for titrations.

It allows you to add a known amount of your titrant to the solution you are testing.

If a pH meter is used, the equivalence point can be measured.

An indicator will give you the endpoint.


Indicator examplesIndicator examples

Acid-base indicators are weak acids that undergo a color change at a known pH.

bromthymol blue

phenolphthalein methyl red


HCl(aq) + NaOH(aq) H2O(l) + NaCl(aq)

All of these reactions occur in solution where the acid and base are separated into their ions.

Na+(aq) + OH-(aq) + H+(aq) + Cl-(aq) H2O(l) + Na+(aq) + Cl-(aq)

The salt is usually in the form of its dissolved ions.


It is the formation of H2O that actually allows the reaction to proceed.

HH++((aq) + OHOH--((aq) HHOHOH(l)(l)

This is the “net ionic”“net ionic” equation for almost all acid/base neutralizationacid/base neutralization reactions.


H2CO3 + 2NaOH Na2CO3 + 2H20

HCL + NaOH NaCl + H20

Salts Salts are formed from neutralization neutralization reactionsreactions.

Acid Base Salt Water


Salts are named after the metalmetal and the acid acid anionanion.

Na2CO3 sodium carbonate

NaClO sodium hypochloriteKH2PO4 potassium dihydrogen phosphate

NaHCO3 sodium bicarbonate


Common laboratoryCommon laboratoryacids and basesacids and bases

Molarity

AcidsAcids Formula (undiluted)nitric HNO3 16

hydrochloric HCl 12sulfuric H2SO4 18acetic HC2H3O2 18

BasesBasesammonium hydroxide NH4OH 15sodium hydroxide NaOH solid


Properties of acidsProperties of acids

• Sour taste.

• Produce H3O+ when dissolved in water.

• Undergo double replacement reactions with solid oxides, hydroxides, carbonates and bicarbonates.

HCl + NaOH NaCl + H2O

2 HCl + CaCO3 CaCl2 + CO2 + H2O

HCl + NaHCO3 NaCl + CO2 + H2O

2 HCl + CuO CuCl2 + H2O


Properties of acidsProperties of acids

Another property is the ability to react with metals, producing hydrogen gas.

Zn + 2 HCl ZnCl2 + HH22(g)(g)

Some metals react better with acids than others. We can show the reactivity using an

activity seriesactivity series


Activity series of metalsActivity series of metals

potassiumsodium

potassiumsodium

calciumcalcium

magnesiumaluminum

zincchromium

magnesiumaluminum

zincchromium

ironnickel

tinlead

ironnickel

tinlead

coppersilver

platinumgold

coppersilver

platinumgold

incr

easi

ng

rea

ctiv

ity

Reacts violently with cold water

Reacts slowly with cold water

Reacts very slowly with steambut quite reactive in acid

Reacts moderately with highlevels of acid

Unreactive in acid


Activity series of metals -Activity series of metals -various metals in HClvarious metals in HCl

Iron Zinc Magnesium


Properties of basesProperties of bases

• Solutions have a slippery or soapy feel.• Will react with acids to produce a salt.

Neutralization reactionNeutralization reaction

NaOH + HCl NaCl + H2O

Neutralization of fatty acids in the skin produce soap. This is why bases feel slippery.


Acid and Base StrengthAcid and Base Strength

Strong acidsStrong acids dissociate completely in water HCl, HBr, HI, HClOHCl, HBr, HI, HClO33, HNO, HNO33, , HClOHClO44, H, H22SOSO44..

Weak acids Weak acids partially dissociate in water. most acids are weak.

Strong basesStrong bases dissociate completely in water NaOH, LiOH, KOH

strong bases are metal hydroxides.

Weak basesWeak bases partially dissociate in water.


DissociationDissociation

Strong acids and basesStrong acids and bases• considered to dissociate completely.

HCl(aq) + H2O(l) H3O+ (aq) + Cl-

(aq)

NaOH(aq) + H2O(l) Na+(aq) + OH-

(aq)

Weak acids and basesWeak acids and bases• do not dissociate completely.

HC2H3O2 (aq) + H2O(l) H3O+(aq) +C2H3O2

-(aq)

NH3 (aq) + H2O(l) NH4+ (aq)+ OH-

(aq)


Acid dissociation constant, KAcid dissociation constant, Kaa

The strength of a weak acid can be expressed as an equilibrium.

HA (aq) + H2O(l) H3O+(aq) + A-

(aq)

The strength of a weak acid is related to its equilibrium constant, Ka.

Ka = [A-][H3O+] [HA]

We omit water.It’s alreadyincluded in

the constant.

We omit water.It’s alreadyincluded in

the constant.


Dissociation of bases,Dissociation of bases,KKbb

The strength of a weak base can also be expressed as an equilibrium.

B (aq) + H2O(l) BHBH++((aq) +OHOH-

(aq)

The strength of a weak base is related to its equilibrium constant, Kb.

Kb = [OH[OH--][BH][BH++]] [B]


KKaa and K and Kbb values values

For weak acids and bases

Ka and Kb always have values that are smaller than one.

• Acids with a larger Ka are stronger than ones with a smaller Ka.

• Bases with a larger Kb are stronger than ones with a smaller Kb.

Most acids and bases are considered weak.


The strengthstrength of an acid is predicated on its ability to dissociate and release Hability to dissociate and release H++,, not on the number of H+ it has available.

Example:Example: Hydrochloric acid (HCl) with only one hydrogen per molecule is a very strong acid whereas Boric acid (H3BO3) with 3X the number of hydrogen’s per molecule is a very weak acid.


*Acids are a lot like peopleAcids are a lot like people: it’s not what you’ve got but what you do with it that really counts.


Some Representative Acids

NAME FORMULA CLASSI-FICATION

H30+ FROM 1,000,000

MOLECULES

IN 0.01M

Sulfuric H2SO4 Strong 1,220,000

Nitric HNO3 Strong 920,000

Hydrochloric HCl Strong 920,000

Phosphoric H3PO4 Moderate 270,000

Lactic Acid CH3CHOHCO2H Weak 87,000

Acetic Acid CH3COOH Weak 13,000

Boric Acid H3BO3 Weak Less Than 1

Hydrocyanic Acid

HCN Weak Less Than 1

Less Than 1

Less Than 1


*No matter how dilute a strong acid may be, it is still a strong acid.

0.001 M HNO3 is a strong acid solution even though dilute.

18 M H2CO3 is a weak acid solution even though concentrated.

DON’T CONFUSE CONCENTRATION WITH DON’T CONFUSE CONCENTRATION WITH STRENGTH !!STRENGTH !!


HYDROLYSIS REACTIONSHYDROLYSIS REACTIONS

The conjugate base of a weak acid is one that has a strong attraction for H+. If a conjugate base of a weak acid is put into H2O, it will try to reform the weak acid by taking a H+ from H2O.

COCO332-2- + H2O HCO3

- + OHOH--





- + OHOH--





- + OHOH--





- + OHOH--





- + OHOH--





- + OHOH--





- + OHOH--


This is why washing soda (Na2CO3) is added to water. The conjugate base reforms the weak acid molecule producing OH- ions and making the water alkaline. Clothes get cleaner in alkaline water.

COCO332-2- + H + H22O HCOO HCO33

-- + + OHOH--


BuffersBuffers

BUFFERS: Control of pH

Our bodies are acid factories.• STOMACH: produces Hydrochloric acid. • MUSCLES: produce Lactic Acid.• STARCHES and SUGARS: Metabolize to

pyruvic acid• CO2 from RESPIRATION: produces

Carbonic acid in the blood


• Our bodies must eliminate or neutralize these acids, because excess acidity in the wrong place will kill us.

• A buffer solution is one in which the pH remains relatively constant even if an acid or base is added.


Chemically, a buffer solution contains a weak acid and one of its’ salts (conjugate base) or a weak base and one of its’ salts (conjugate acid).

HHAA(aq)(aq) + H + H22OO(l)(l) H H33OO++(aq)(aq) + + AA--

((aq)aq)

Add OH- Add H+

shift to right shift to left

Based on LeChatelier’s Principle.


Ex. H2CO3 + H20 HCO3- + H30+

H2PO4- + H20 HPO4

-2 + H30

NH3 + H20 NH4+ + OH-

H2CO3 / HCO3-

Acid Conjugate base (salt)

H2PO4- / HPO4

-2

Acid Conjugate base (salt)

NH3 / NH4+

Base Conjugate acid (salt)


How does a buffer work?How does a buffer work?

The salt portion (conjugate baseconjugate base) of the pair combines with H+ to form the acid molecule.

H+ + HCO3- H2CO3


If the acidity starts to drop too much, the acid portion of the buffer pair dissociates to provide H+.

H2CO3 HH++ + HCO3-


Example: Physiological salinePhysiological saline is equivalent to a 0.15 M NaCl solution and its pH is 7.0.

Blood plasmaBlood plasma would be like this solution but it has a buffer of HCOHCO33

--/H/H22COCO33 in a 20:1 ratio that pushes the pH to 7.4.

If 1 ml of 10.0 M HCl was added to 1 liter of the unbuffered saline, the pH value of 7.0 would immediately drop to a pH = 2.0. (An increase in acidity of 100,000.)


In the blood, the H+ is absorbed by HCO3-.

ex. H+ + HCO3- H2CO3

This prevents the pH from drastically changing.

If we had added 1 ml of 10 M HCl to our buffered blood, the pH would go from 7.4 to 7.2.


This small increase in our blood of the H2CO3 is still a problem. A pH of 7.2 is far too low and would create a condition called acidosis.

But our body is capable of removing this H2C03 from the blood through hyperventilation (increased breathing rate).

HOW????


1. H2CO3 is formed in the blood

((HCOHCO33-- + H + H++ HH22COCO33))

2. It is carried to the lungs where it will decompose to form CO2.

((HH22COCO33 HH220 + CO0 + CO22))

3. Rapid breathing expels the CO2.


When the pH of our blood goes up (alkalosis), the other partner in the buffer pair goes to work.

OH- + H2CO3 H20 + HCO3-

Now we are losing H2CO3 and getting too much HCO3

- in the blood. To return the HCO3

-/H2CO3 to normal, our body goes into action.


1. CO2 is kept in body by slower and shallower breathing (hypoventilation).(Breathing into a paper bag helps.)(Breathing into a paper bag helps.)

2. This allows more H2CO3 to form (CO2 + H20 H2CO3).

3. Kidneys remove excess HCO3- and

release more H+ to blood.


DiabetesDiabetes MellitusMellitusTransport of glucose (blood sugar) across cell membranes is interrupted.

Sugar thus remains in blood (hyperglycemiahyperglycemia).

Most body tissues must switch over to fat metabolism. (Low carbohydrate diets also Low carbohydrate diets also cause this to happen.)cause this to happen.)


Acetyl Coenzyme AAcetyl Coenzyme A is formed at excessive rate.

This overloads the Krebs Cycle and body tries to dispose of it by conversion to ketones.ketones. (Often observed as release of acetoneacetone via the breath.)

These ketone bodies are acidic.AcidosisAcidosis soon follows. (pH drops)


Acidic bloodAcidic blood cannot transport oxygen very well.

Breathing becomes labored and painful.

DiabeticDiabetic comacoma can follow.


StarvationStarvation:: Body's glycogen stores are depleted rapidly and the body calls on its fat reservesfat reserves. Fat is taken first from around the kidneys and the heart. Then it is removed from other parts of the body, eventually even the bone marrowbone marrow is depleted.

By the same mechanism discussed above, starvationstarvation also leads to ketosis ketosis which rapidly develops into acidosis.acidosis.

Documents

9 - 1Chemistry for Allied Health: Chapter 10 Acids and Bases Acids & Bases Ionization of Water pH Acid-Base Reactions Salt Solutions BuffersDilutionsTitrations