Acids and Acids and BasesBases

Acid and Base DefinitionsAcid and Base Definitions19.1

Acid PropertiesAcid Properties Water solutions of acids conduct electricityWater solutions of acids conduct electricity Acids often react with metal to produce Acids often react with metal to produce

hydrogen gashydrogen gas Acids change color indicatorsAcids change color indicators Acid + Base Acid + Base → Salt + Water→ Salt + Water Acids have sour taste—don’t try thisAcids have sour taste—don’t try this Acids react with carbonates to produce Acids react with carbonates to produce

carbon dioxidecarbon dioxide Acids sting skinAcids sting skin

BasesBases

Water solutions of bases conduct Water solutions of bases conduct electricityelectricity

Bases change color indicatorsBases change color indicators Acid + Base Acid + Base → Salt + Water→ Salt + Water Bases have a bitter taste—don’t try thisBases have a bitter taste—don’t try this Bases react with fat to make soapBases react with fat to make soap Bases have slippery feelBases have slippery feel Strong bases are caustic to skinStrong bases are caustic to skin

The pH scale.The pH scale.pH = -log [H+]pH = -log [H+]

Examples:Examples:

1.1. Find the pH of a solution if Find the pH of a solution if the hydrogen ion the hydrogen ion concentration is 0.027M.concentration is 0.027M.

2.2. Find the pH of a solution Find the pH of a solution where 0.03 moles of HCl is where 0.03 moles of HCl is dissolved into 0.2 liters of dissolved into 0.2 liters of water.water.

1313 Oven Cleaner/DranoOven Cleaner/Drano

12 12 Hair removerHair remover

11 Ammonia11 Ammonia

10 Soap10 Soap

99 Baking Soda, bleach, antacidsBaking Soda, bleach, antacids

88 ShampooShampoo

77 Water, blood, eggs, baby shampooWater, blood, eggs, baby shampoo

66 Urine, milk, salivaUrine, milk, saliva

55 Coffee, bread, rainwaterCoffee, bread, rainwater

44 TomatoesTomatoes

33 Vinegar, soda, beerVinegar, soda, beer

22 Stomach acid, lemon juiceStomach acid, lemon juice

11 Battery acidBattery acid

pHpH of Various solutions

Acid & Base StrengthAcid & Base Strength

Strong acids and bases completely Strong acids and bases completely ionize (separate) in solutionionize (separate) in solution• Acids: Nitric, sulfuric, hydrobromicAcids: Nitric, sulfuric, hydrobromic• Bases: sodium hydroxide, potassium Bases: sodium hydroxide, potassium

hydroxide hydroxide Weak acids and bases slightly ionizeWeak acids and bases slightly ionize

• Acids: Acetic, carbonic, hydrofluoricAcids: Acetic, carbonic, hydrofluoric• Bases: Ammonium hydroxideBases: Ammonium hydroxide

Common Aqueous Acids

Chapter 14Section 1 Properties of Acids and Bases

Acid and Base TypesAcid and Base Types Monoprotic acidsMonoprotic acids

• HClHCl Monobasic basesMonobasic bases

• NaOHNaOH Diprotic AcidDiprotic Acid

• HH22SOSO44,,HH22COCO33

Triprotic AcidTriprotic Acid• HH33POPO44

Dibasic BasesDibasic Bases• Ca(OH)Ca(OH)22, Mg(OH), Mg(OH)22

“polyprotic”

19.1

Acids and BasesAcids and Bases

Hydrochloric AcidHydrochloric Acid

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Some DefinitionsSome Definitions ArrheniusArrhenius

• An acid is a substance that, when An acid is a substance that, when dissolved in dissolved in water, increases the water, increases the concentration of hydrogen ions.concentration of hydrogen ions.

HCl → HHCl → H++ + Cl + Cl--

• A base is a substance that, when A base is a substance that, when dissolved in water, increases the dissolved in water, increases the concentration concentration of hydroxide ions.of hydroxide ions.

NaOH → NaNaOH → Na++ + OH + OH--

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Brønsted-Lowry Theory of Acids Brønsted-Lowry Theory of Acids and Basesand Bases

An acid is a proton donor.An acid is a proton donor. A base is a proton acceptor.A base is a proton acceptor.

HCl + HHCl + H22O → HO → H33OO++ + Cl + Cl--

HCl is an acid because it donates a HCl is an acid because it donates a proton to water.proton to water.

Hydronium Ion: HHydronium Ion: H33OO++ • This is a hydrated protonThis is a hydrated proton

Brønsted-Lowry Theory of Acids Brønsted-Lowry Theory of Acids and Basesand Bases

An acid is a proton donor.An acid is a proton donor. A base is a proton acceptor.A base is a proton acceptor. NaNa22COCO33 is a Bronsted-Lowry base because the is a Bronsted-Lowry base because the

carbonate ion accepts a proton from water.carbonate ion accepts a proton from water. Water is an acid because it donates a proton Water is an acid because it donates a proton

to the carbonate ion.to the carbonate ion.

COCO332-2- + H + H22O ↔ OHO ↔ OH-- + HCO + HCO33

--

Notice that we ignore the sodium ion because Notice that we ignore the sodium ion because it is neutral.it is neutral.

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Why Ammonia is a Base?Why Ammonia is a Base?

Brønsted-Lowry Acids and Brønsted-Lowry Acids and BasesBases

A water molecule that gains a hydrogen ion A water molecule that gains a hydrogen ion becomes a positively charged hydronium ion becomes a positively charged hydronium ion (H(H33OO++).).

19.1

19.1

© 2009, Prentice-Hall, Inc.

Lewis AcidsLewis Acids

Lewis acids are defined as electron-pair Lewis acids are defined as electron-pair acceptors.acceptors.

Atoms with an empty valence orbital can be Atoms with an empty valence orbital can be Lewis acids.Lewis acids.

© 2009, Prentice-Hall, Inc.

Lewis BasesLewis Bases

Lewis bases are defined as electron-pair Lewis bases are defined as electron-pair donors.donors.

Anything that could be a Brønsted-Lowry Anything that could be a Brønsted-Lowry base is a Lewis base.base is a Lewis base.

Lewis bases can interact with things other Lewis bases can interact with things other than protons, however.than protons, however.

Acid and Base DefinitionsAcid and Base Definitions19.1

•A A conjugate acid-base pairconjugate acid-base pair consists of consists of two substances related by the loss or two substances related by the loss or gain of a single hydrogen ion.gain of a single hydrogen ion.

19.1

Conjugate Acid-Base PairsConjugate Acid-Base Pairs

19.1

Conjugate Acids and Bases

The species that remains after a Brønsted-Lowry acid has given up a proton is the conjugate base of that acid.

aq + l aq + aq–2 3HF( ) H O( ) F ( ) H O ( )

Chapter 14

acid conjugate base

Conjugate Acids and Bases, continued

Brønsted-Lowry acid-base reactions involve two acid-base pairs, known a conjugate acid-base pairs.

aq + l aq + aq–2 3HF( ) H O( ) F ( ) H O ( )

Chapter 14

acid1 base2 base1 acid2

Conjugate Acids and Bases, continued

Strength of Conjugate Acids and Bases• The stronger an acid is, the weaker its

conjugate base

• The stronger a base is, the weaker its conjugate acid

g + l aq + aq–2 3HCl( ) H O( ) H O ( ) Cl ( )

Chapter 14

strong acid base acid weak base

Conjugate Acids and BasesStrength of Conjugate Acids and Bases

Proton transfer reactions favor the production of the weaker acid and the weaker base.

aq + l aq + aq–4 2 3 4HClO ( ) H O( ) H O ( ) ClO ( )

aq + l aq + aq–3 2 3 3CH COOH( ) H O( ) H O ( ) CH COO ( )

Chapter 14

stronger acid stronger base weaker acid weaker base

The reaction to the right is more favorable

weaker acid weaker base stronger acid stronger base

The reaction to the left is more favorable

Relative Strengths of Acids and Bases

Amphoteric Compounds

Any species that can react as either an acid or a base is described as amphoteric.

example: waterwater can act as a base

aq + l aq + aq–2 4 2 3 4H SO ( ) H O( ) H O ( ) HSO ( )

g + l aq aq–3 2 4NH ( ) H O( ) NH ( ) OH ( )

acid1 base2 acid2 base1

water can act as an acid

base1 acid2 acid1 base2

Oxyacids of ChlorineOxyacids of ChlorineChapter 14

Section 3 Acid-Base Reactions

pHpH

pH = -log [HpH = -log [H++]] (acid concentration)(acid concentration) pOH = -log [OHpOH = -log [OH--] ] (base concentration)(base concentration)

For aqueous solutions at 25 For aqueous solutions at 25 °C:°C:• [H[H++] [OH] [OH--] = 1.0 x 10] = 1.0 x 10-14 -14 = K= Kww

This is called the “ion product constant” for This is called the “ion product constant” for waterwater

• pH + pOH = 14pH + pOH = 14

19.2

Measuring pHMeasuring pH

Universal IndicatorsUniversal Indicators

19.2

Measuring pHMeasuring pH19.2

Neutralization ReactionsNeutralization ReactionsChapter 14

Amphoteric Compounds, continued–OH in a Molecule

• The covalently bonded IOH group in an acid is referred to as a hydroxyl group.

• Molecular compounds containing —OH groups can be acidic or amphoteric.

• The behavior of a compound is affected by the number of oxygen atoms bonded to the atom connected to the —OH group.

Section 3 Acid-Base Reactions

Other Acid Base FactsOther Acid Base Facts

Water is able to self ionizeWater is able to self ionize

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

When H+ ion are in solution, they When H+ ion are in solution, they always join with a water molecule to always join with a water molecule to form a hydronium ionform a hydronium ion

HH++ + H + H22O O H H33OO++

KKaa Acid Ionization Constant Acid Ionization Constant

KKaa = [H = [H++] [A] [A--]]

[HA] [HA]A 0.1M solution of ethanoic acid is found to have A 0.1M solution of ethanoic acid is found to have [H+]=4.2 x 10[H+]=4.2 x 10-3-3. Calculate the acid dissociation . Calculate the acid dissociation constant.constant.

KKaa = [H = [H++] [A] [A--]] [HA] [HA]

KKa a = (4.2 x 10= (4.2 x 10-3-3)(4.2 x 10)(4.2 x 10-3-3) = 1.8 x 10) = 1.8 x 10-4-4

0.1 - 4.2 x 100.1 - 4.2 x 10-3-3

Buffer SolutionsBuffer Solutions Solutions that resist change in pH when acids or Solutions that resist change in pH when acids or

bases are added to them.bases are added to them. Formed by mixing a weak acid and its saltFormed by mixing a weak acid and its salt

• HCHC22HH33OO22 + NaC + NaC22HH33OO22

When NaOH is added to the solution, HCWhen NaOH is added to the solution, HC22HH33OO2 2

reacts and consumes the OHreacts and consumes the OH-- ions ions When HCl is added to the solution, the HWhen HCl is added to the solution, the H++ ions ions

react with the acetate ions from the saltreact with the acetate ions from the salt

Results: buffer solution resist changes in pH!Results: buffer solution resist changes in pH! Buffer solutions are important in maintaining Buffer solutions are important in maintaining

blood pH.blood pH.

Amphoteric SubstancesAmphoteric Substances

Substances that can act as acids or basesSubstances that can act as acids or bases• Remember:Remember:

Acids are proton donorsAcids are proton donors Bases are proton acceptorsBases are proton acceptors

Ex. Bisulfate ion: HSOEx. Bisulfate ion: HSO44--

HSOHSO44- - ++ HH+ + →→ H H22SOSO44

HSOHSO44- - ++ OHOH- - →→ H H22O + SOO + SO44

2-2-

19.2

TitrationTitration

Titration is the process of determining the Titration is the process of determining the concentration of an unknown solution concentration of an unknown solution through volumetric analysisthrough volumetric analysis

When an acid and base are mixed, for When an acid and base are mixed, for neutralization to occur:neutralization to occur:

nnAA=n=nBB

MMacidacid x V x Vacid acid = M = Mbasebase x V x Vbasebase

Microscopic viewMicroscopic viewof the solutions of the solutions

in the titration of in the titration of 0.200 0.200 MM HNO HNO33

with 0.100 with 0.100 M M NaOH.NaOH.

End point is when the color change occurs

Macid x Vacid = Mbase x Vbase

0.2M x 50mL = 0.1M x Vbase

Vbase = 100mL

The pH curve for the titration of 50.0 mL of The pH curve for the titration of 50.0 mL of 0.200 0.200 MM HNO HNO33 with 0.100 with 0.100 M M NaOH.NaOH.

Titration ProblemsTitration Problems

A solid mixture contains NaOH and A solid mixture contains NaOH and NaCl. If 10 ml of 0.1 M HCl is required NaCl. If 10 ml of 0.1 M HCl is required to titrate a 0.1 g sample of this to titrate a 0.1 g sample of this mixture to its end point, what is the mixture to its end point, what is the percent NaOH in the sample? percent NaOH in the sample?

1 mole of HCl neutralizes 1 mole of 1 mole of HCl neutralizes 1 mole of NaOHNaOH

How many moles of HCl are How many moles of HCl are required to complete titrationrequired to complete titration

Titration ProblemsTitration Problems

20 ml of an aqueous base Ca(OH)20 ml of an aqueous base Ca(OH)22 is used is used in titration with a color indicator. If 25 ml in titration with a color indicator. If 25 ml of 0.05M HCl is required to reach the end of 0.05M HCl is required to reach the end point, what is the concentration of the point, what is the concentration of the Ca(OH)Ca(OH)22??

Balance Equation:Balance Equation:2HCl + Ca(OH)2HCl + Ca(OH)2 2 → CaCl→ CaCl22 + 2H + 2H22OO

moles of acid = 2 x moles of basemoles of acid = 2 x moles of base• Therefore Therefore MMacidacid x V x Vacid acid = 2 x M = 2 x Mbasebase x V x Vbasebase

Titration Curve for NaOHand HCLTitration Curve for NaOHand HCLpH13121110987654321

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Volume HCl