Unit VI Unit VI Acids, Bases & SaltsAcids, Bases & Salts

TextboTextbookok Chapter 15Chapter 15

Unit Outline Image taken from http://www.mhhe.com/physsci/chemistry/chang7/esp/

folder_structure/cr/m3/s3/assets/images/crm3s3_1.jpg on 8/14/09.

Image taken on 8/13/09.

ElectrolytesElectrolytes Dissolve in water, solution Dissolve in water, solution

formed will conduct formed will conduct electricity. electricity. Why conduct?Why conduct?

Conductivity due to Conductivity due to presence of free ions. presence of free ions. How How free ions?free ions?

Free ions can be created Free ions can be created from processes of from processes of dissociation or ionization.dissociation or ionization.

Acids, Bases & Salts are Acids, Bases & Salts are examples of electrolytes.examples of electrolytes.

Electrolytes Poem

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DissociationDissociation Occurs when ions of an Occurs when ions of an ionic solidionic solid are are

separatedseparated from the crystal latticefrom the crystal lattice structure. structure. Polar water molecules pull ions from lattice, Polar water molecules pull ions from lattice,

surround ions and form hydrated ions.surround ions and form hydrated ions. Examples: all ionic compounds (salts) such Examples: all ionic compounds (salts) such

as NaCl(aq), CuSOas NaCl(aq), CuSO44(aq), MgBr(aq), MgBr22(aq)(aq)

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Cations are positive.Anions are negative.

IonizationIonization

Occurs when a Occurs when a molecular solidmolecular solid is dissolved and is dissolved and creates ions in solution. creates ions in solution.

Unlike dissociation, ions were not present originally.Unlike dissociation, ions were not present originally. Common examples: AcidsCommon examples: Acids

HCHC22HH33OO22 H2OH2O> H> H++(aq) + C(aq) + C22HH33OO22--(aq)(aq)

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Weak or Strong Electrolyte?Weak or Strong Electrolyte? Depends on amount of ionization.Depends on amount of ionization. Reference Tables K & L list strong electrolytes Reference Tables K & L list strong electrolytes

closer to the top (stronger acids and bases)closer to the top (stronger acids and bases) KKeq eq values such as Kvalues such as Kaa or K or Kbb can indicate amount of can indicate amount of

ionization. (Remember Kionization. (Remember Keqeq’s ’s ΔΔ only w/ temp.)only w/ temp.) Large Ka Large Ka strong electrolyte (acid); many free strong electrolyte (acid); many free

ionsions Small Ka Small Ka weak electrolyte (acid); few free ions weak electrolyte (acid); few free ions

1. Complete ionization of HCl animation

2. Incomplete ionization of weak acid animation

3. Comparing HCl ionization to HF ionization animation

4. Conductivity of HCl vs. Acetic Acid video

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NonelectrolytesNonelectrolytes Do not conduct Do not conduct

electricity when in electricity when in solution.solution.

Examples: All organic Examples: All organic compounds except compounds except organic acids. organic acids.

Examples: Examples: CC1212HH2222OO1111(aq), (aq), CC22HH55OH(aq)OH(aq)

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AB(s) AB(aq) {no free ions}

How do you define How do you define something?something? OperationalOperational Definition- Definition-

list properties or list properties or behaviors. Include behaviors. Include observationsobservations from from experiments.experiments.

ConceptualConceptual Definition- Definition-tries to answer tries to answer “Why?” and “How?”. “Why?” and “How?”. Based on Based on interpretations or interpretations or conclusionsconclusions from from observed facts.observed facts.

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What is an Acid?What is an Acid?6 Operational Definitions of an 6 Operational Definitions of an

AcidAcid

#6Metallic oxides

#5Sour

#4Neutralization

#3Indicators

#2Metals H2(g)

#1Electrolyte

What is an Acid?

Bases

Acids: Op Def #1Acids: Op Def #11.1. Aqueous solutions Aqueous solutions

of acids conduct of acids conduct electricityelectricity Weak acidsWeak acidsweak weak

electrolyteelectrolytefew few ionsionsslight slight ionizationionization

Strong Strong acidsacidsstrong strong electrolyteelectrolyteMany Many ionsionsAlmost Almost complete ionizationcomplete ionization

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Chinese for strong electrolyte (strong acid) ???

Acids: Op Def #2Acids: Op Def #22.2. Acids will react with certain active metals Acids will react with certain active metals

to liberate hydrogen gas.to liberate hydrogen gas. Think Rocket Lab! Think Rocket Lab! 2HCl(aq) + Zn(s) 2HCl(aq) + Zn(s) ZnCl ZnCl22(s) + H(s) + H22(g)(g) Use Ref Table J. Where are metals found on Use Ref Table J. Where are metals found on

table that will undergo this reaction?table that will undergo this reaction?

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Acids: Op Def #3Acids: Op Def #33.3. Acids cause color changes for acid-base indicators. Acids cause color changes for acid-base indicators.

See Ref Table M. See Ref Table M. Note from Table M that all indicators have their Note from Table M that all indicators have their

own pH range. Depends on the concentration of own pH range. Depends on the concentration of H+ in solution. Indicators do not change right at H+ in solution. Indicators do not change right at pH of 7.pH of 7.

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Acids: Op Def #4Acids: Op Def #44.4. Acids react with hydroxides (bases) Acids react with hydroxides (bases)

to form water and a salt. Called to form water and a salt. Called neutralization.neutralization.

Example: Example: HNOHNO33(aq) + NaOH(aq) (aq) + NaOH(aq) H H22O + NaNOO + NaNO33(aq)(aq)

Remember from Lab activity to make Remember from Lab activity to make salt!!!salt!!!

Neutralization simplified: Neutralization simplified: HH++(aq) + OH(aq) + OH--(aq) (aq) H H22OO

Try another example on next slide!Try another example on next slide!

What is a salt?

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Acids react with carbonates Acids react with carbonates to release carbon dioxide.to release carbon dioxide.

HCl(aq) + LiHCl(aq) + Li22COCO33(s) (s) complete this complete this rxnrxn

2HCl(aq) + Li2HCl(aq) + Li22COCO33(s) (s) LiCl(aq) + H LiCl(aq) + H22COCO33 Unstable and decomposesUnstable and decomposes

2HCl(aq) + Li2HCl(aq) + Li22COCO33(s) (s) LiCl(aq) LiCl(aq) + H+ H22O(l) + COO(l) + CO22(g)(g)

Acids: Op Def #5Acids: Op Def #55.5. Dilute aqueous Dilute aqueous

solutions of acids solutions of acids have a sour taste.have a sour taste.

Examples: vinegar Examples: vinegar (acetic acid) in (acetic acid) in pickles, citric acid in pickles, citric acid in lemonheads/sour lemonheads/sour candy or citrus candy or citrus fruits (lemons, fruits (lemons, limes, oranges, etc.)limes, oranges, etc.)

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graphics/ctpcs/ctpc10-011a.jpg on 8/14/09.

Acids: Op Def #6Acids: Op Def #66.6. Acids react with Acids react with

metallic oxides to metallic oxides to form salts and form salts and water.water.

Example: Example: 2HCl 2HCl + K+ K22O O 2KCl +H 2KCl +H22OO

Potassium Oxide

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What is a Base?What is a Base?5 Operational Definitions of a 5 Operational Definitions of a

BaseBase

#5Caustic

#4Bitter

#3Neutralization

#2Indicators

#1Electrolyte

What is a Base?

Conceptual Definitions

Bases: Op Def #1Bases: Op Def #11.1. Aqueous solutions of Aqueous solutions of

bases conduct bases conduct electricityelectricity

Weak basesWeak basesweak weak electrolyteselectrolytesfew few ionsionsslight dissociationslight dissociation

Strong basesStrong basesstrong strong electrolyteselectrolytesMany Many ionsionsAlmost complete Almost complete dissociationdissociation

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Bases: Op Def #2Bases: Op Def #22.2. Bases cause color Bases cause color

changes in acid-changes in acid-base indicators. base indicators. See Ref Table M.See Ref Table M.

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Bases: Op Def #3Bases: Op Def #33.3. Bases react with acids to form water Bases react with acids to form water

and a salt. Called neutralization.and a salt. Called neutralization. Example: Example:

HCHC22HH33OO22(aq) + NaOH(aq) (aq) + NaOH(aq) H H22O + NaCO + NaC22HH33OO22(aq)(aq)

Neutralization simplified: Neutralization simplified: HH++(aq) + OH(aq) + OH--(aq) (aq) H H22OO

What is a salt?

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Bases: Op Def #4Bases: Op Def #44.4. Aqueous solutions Aqueous solutions

of bases feel of bases feel slippery and taste slippery and taste bitter.bitter.

Examples: soaps, Examples: soaps, cleanerscleaners

Image taken from http://www.carpages.co.uk/news/tyre-cleaner-14-07-05.asp on 8/14/09.

Armor All is great on tires and the dusty dashboard. Why never on the steering wheel?

Bases: Op Def #5Bases: Op Def #55.5. Strong bases have Strong bases have

a caustic action on a caustic action on the skin, corrosive the skin, corrosive to skin and to skin and poisonous.poisonous.

Examples: really Examples: really strong cleaners, strong cleaners, concentrated concentrated solutions of KOH or solutions of KOH or NaOH can cause NaOH can cause blindness if in eyesblindness if in eyes

Image taken from http://wpcontent.answers.com/wikipedia/commons

/thumb/0/09/Sodium_hydroxide_burn.png/180px-Sodium_hydroxide_burn.png on 8/14/09.

Burn from conc. NaOH

2 Conceptual Definitions of 2 Conceptual Definitions of Acids and BasesAcids and Bases

Remember conceptual definitions add Remember conceptual definitions add reasons to observations. Answer Why?reasons to observations. Answer Why?

1)1) Arrhenius TheoryArrhenius Theory2)2) BrBröönsted-Lowry Theory (AKA an nsted-Lowry Theory (AKA an alternate alternate

acid/base theoryacid/base theory according to NYSED) according to NYSED)

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Arrhenius’ Theory of an Acid Arrhenius’ Theory of an Acid (1887)(1887)

A substance that A substance that yields hydrogen yields hydrogen ions (Hions (H++) in ) in aqueous solutions.aqueous solutions.

Arrhenius said Arrhenius said properties of acids properties of acids in aqueous in aqueous solutions due to an solutions due to an excess of Hexcess of H++ or or HH33OO+ +

(hydrogen or hydronium ions)(hydrogen or hydronium ions)

Good definition but Good definition but limited to only (aq).limited to only (aq).

Examples:

HNO3 H2O H+(aq) + NO3

-(aq)

H2SO4 H2O 2H+(aq) + SO4

2-

(aq)

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Svante Arrhenius,The Nobel Prize in Chemistry 1903

Arrhenius’ Theory of a Base Arrhenius’ Theory of a Base (1887)(1887) A substance that yields hydroxide ions A substance that yields hydroxide ions

(OH(OH--) as the only negative ions in aqueous ) as the only negative ions in aqueous solutions.solutions.

Examples:

KOH H2O K+(aq) + OH-(aq)

Ba(OH)2 H2O Ba+2(aq) + 2OH-(aq)

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BrBröönsted-Lowry Theory of an Acid nsted-Lowry Theory of an Acid (1923)(1923)

Any species Any species (molecule or ion) (molecule or ion) that can donate a that can donate a proton to another proton to another species.species.

AKA: “a proton AKA: “a proton donor”donor”

BrBröönsted-Lowry does nsted-Lowry does not replace Arrhenius’ not replace Arrhenius’ theory, it just extends theory, it just extends it. Includes Arrhenius it. Includes Arrhenius examples of acids but examples of acids but adds other examples.adds other examples.

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Daris%20Qodarisman%20N_0605524/Gambar/Bronsted.gif on 8/14/09.

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/~ekatz/scientists/lowry1.JPGon 8/14/09.

Thomas Martin Lowry

Johannes Nicolaus Brønsted

BrBröönsted-Lowry Theory of a Base nsted-Lowry Theory of a Base (1923)(1923)

Any species(molecule or ion) that can accept a Any species(molecule or ion) that can accept a proton.proton.

AKA: “a proton acceptor”AKA: “a proton acceptor” Again BrAgain Bröönsted-Lowry does not replace Arrhenius’ nsted-Lowry does not replace Arrhenius’

theory, it just extends it. More species can accept theory, it just extends it. More species can accept a proton than just an OHa proton than just an OH--..

Ex: HEx: H22O + HCl O + HCl ⇆⇆ H H33OO++ + Cl + Cl-- Water is base in forward rxn, accepts HWater is base in forward rxn, accepts H++ to become H3O to become H3O++

In reverse rxn, ClIn reverse rxn, Cl-- accepts proton and acts as base to form HCl accepts proton and acts as base to form HCl

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/science/chemistry/base.gif on 8/31/09.

I luv accepti

ng protons.

B-L Conjugate Acid-Base PairsB-L Conjugate Acid-Base Pairs Bronsted-Lowry acid-base rxn,Bronsted-Lowry acid-base rxn,

Transfer of proton (HTransfer of proton (H++) from acid to base) from acid to base To accept proton, must have pair of unshared electrons.To accept proton, must have pair of unshared electrons. An acid give a proton to form a conjugate base.An acid give a proton to form a conjugate base. A base gains a proton to form a conjugate acid.A base gains a proton to form a conjugate acid.

Ex: HSOEx: HSO44-- + H + H22O O H H33OO++ + SO + SO44

2-2-

Label reacting acid and base and conjugates formed.Label reacting acid and base and conjugates formed. Do Examples!Do Examples!

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Lewis A&B TheoryLewis A&B Theorydefined in terms of electron pairdefined in terms of electron pair

Lewis acids- electron-pair acceptorLewis acids- electron-pair acceptorLewis bases- electron pair donor.Lewis bases- electron pair donor.

Remember coordinate covalent bonds?

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Amphoteric(Amphiprotic) Amphoteric(Amphiprotic) SubstancesSubstances

Can act as either an acid or a base.Can act as either an acid or a base. Pick out the amphoteric substances in the Pick out the amphoteric substances in the

following:following:1)1) NHNH33 + H + H22O O ⇆ ⇆ NHNH44

++ + OH + OH--

2)2) HH22O + HCl O + HCl ⇆⇆ H H33OO++ + Cl + Cl--

3)3) NHNH33 + OH + OH-- ⇆⇆ NH NH22-- + H + H22OO

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Naming AcidsNaming Acids Binary acids (2 elements) use hydro……ic Binary acids (2 elements) use hydro……ic

acidacid ex: HCl hydroex: HCl hydrochlorchloric acidic acid Ternary acids (3 elements) use polyatomic Ternary acids (3 elements) use polyatomic

ion name and change endingion name and change endingateate ic ic ite ite ous ous

Ex: HEx: H22SOSO44

(sulfate) Sulfuric acid (sulfate) Sulfuric acid

Ex: HEx: H22SOSO33

(sulfite) Sulfurous acid(sulfite) Sulfurous acid

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Naming SaltsNaming Salts Binary saltsBinary salts

Change ending to ideChange ending to ide Use Roman numeral if Use Roman numeral if

necessary.necessary. Ex: CuClEx: CuCl22

Copper (II) chlorideCopper (II) chloride Ternary saltsTernary salts

Use polyatomic ion Use polyatomic ion namename

Use Roman numeral if Use Roman numeral if necessary.necessary.

Ex: CaEx: Ca33(PO(PO44))22 Calcium phosphateCalcium phosphate

What is a salt?

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Naming BasesNaming Bases What is the ion Arrhenius said all bases What is the ion Arrhenius said all bases

have?have? Use it to name bases. Use Roman Use it to name bases. Use Roman

numeral if necessary.numeral if necessary.Ex: Ba(OH)Ex: Ba(OH)22

Barium hydroxideBarium hydroxide

Ex: Fe(OH)Ex: Fe(OH)22

Iron (II) hydroxideIron (II) hydroxide

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NeutralizationNeutralizationA + B A + B water + salt water + saltComplete and balance the following Complete and balance the following

neutralization rxn: HNOneutralization rxn: HNO33 + Ca(OH) + Ca(OH)22 2HNO2HNO33 + Ca(OH) + Ca(OH)22 2H 2H22O + Ca(NOO + Ca(NO33))22

Name all compounds in this rxn.Name all compounds in this rxn.

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HydrolysisHydrolysisThe reverse of neutralization.The reverse of neutralization.Some salts in aqueous solutions Some salts in aqueous solutions

react with water and form solutions react with water and form solutions that are acidic or basic.that are acidic or basic.

Salt + HSalt + H22O O Acid + Base Acid + Base

Image taken from http://www.elmhurst.edu/~chm/vchembook/182bases.html on 8/14/09.

Examples of HydrolysisExamples of Hydrolysis Salt made from strong acid and weak base give Salt made from strong acid and weak base give

aq solutions that are acidic.aq solutions that are acidic. Ex: NHEx: NH44Cl + HCl + H22O O HCl + NH HCl + NH44OHOH

Salts from weak acids and strong bases give aq Salts from weak acids and strong bases give aq solutions that are basic.solutions that are basic. Ex: NaCEx: NaC22HH33OO22 + H + H22O O HC HC22HH33OO22 + NaOH + NaOH

Salts from strong acid and strong base usually Salts from strong acid and strong base usually do not hydrolyze. If they do, form neutral pH of do not hydrolyze. If they do, form neutral pH of 7.7. Ex: NaOH and HClEx: NaOH and HCl

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Acid-Base Titration:Acid-Base Titration:a very precise a very precise neutralizationneutralization

The molarity (strength) of The molarity (strength) of an acid (or base) of an acid (or base) of unknown concentration can unknown concentration can be determined by slowly be determined by slowly combining it with a base (or combining it with a base (or acid) of known molarity acid) of known molarity (standard solution).(standard solution).

A titration is finished when A titration is finished when the the equivalence or end equivalence or end pointpoint is reached, this is reached, this indicates neutralization and indicates neutralization and is determined from color is determined from color changes of indicators.changes of indicators.

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manuals/114/images/ABTitr01.gif on 8/14/09.

Buret

Titration FormulaTitration FormulaRef Table TRef Table T

Show derivation of Show derivation of formula on formula on overhead.overhead.

Before using Before using titration formula, titration formula, determine mole determine mole ratio of acid:base ratio of acid:base from balanced from balanced equation.equation.

Practice Examples!Practice Examples!

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MAVA = MBVB

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Ionization ConstantsIonization Constants Remember KRemember Keqeq from last from last

unit?unit? In this unit we deal mainly In this unit we deal mainly

with ionization of acids (Kwith ionization of acids (Kaa) ) and bases (Kand bases (Kbb))

KKaa & K & Kbb provide method for provide method for comparing relative strength comparing relative strength of acids or bases.of acids or bases.

Example below:Example below:CHCH33COOH COOH H20H20> H> H++(aq) + CH(aq) + CH33COOCOO--

(aq)(aq)

Size of Ka value tells strength of acid

NYS Chem Reference Table pre-2002

Ionization Constant for Water Ionization Constant for Water (K(Kww))

HH22OO H H++ + OH + OH- - oror 2H2H220 0 H H33OO++ + OH + OH--

Since concentration of H2O is relatively constant, Keq expression can be simplified to ….

Image taken from http://www.elmhurst.edu/~chm/vchembook/images2/184waterequi.gif on 8/31/09.

At STP only 1.0 X 10-7 moles/L of H2O will ionize into equal amts of H+ & OH- so therefore….

KKww = [H = [H++][OH][OH--]]KKww = [1.0X10 = [1.0X10-7-7][1.0X10][1.0X10-7-7]**]**KKww = 1.0X10 = 1.0X10-14-14****

** This is why water is neutral. Because acidity (H+) ** This is why water is neutral. Because acidity (H+) and basicity (OH-) are in equal concentrations.and basicity (OH-) are in equal concentrations.

KKww = 1.0X10 = 1.0X10-14-14 @ 25 @ 25ooC w/standard pressure.C w/standard pressure.

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Sample ProblemWhat happens to [H+] if [OH-]

concentration jumps to 1.0X10-5 @ STP?

Kw = [H+][OH-]

1.0X10-14 = [H+][1.0X10-5][1.0X10-14]/ [1.0X10-5] = [H+][H+] = [1.0X10-9]

[OH-] got bigger, [H+] got smaller

What do you know about the pH What do you know about the pH scale?scale? 0-140-14

7 is neutral7 is neutral Acids below 7, Bases above 7.Acids below 7, Bases above 7. Stronger the acid or base the further away from Stronger the acid or base the further away from

neutral.neutral.

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pHpH pH is the logarithm of the reciprocal of the pH is the logarithm of the reciprocal of the

HH++ concentration concentration pH of a solution tells the concentration of pH of a solution tells the concentration of

HH++ (how acidic it is) (how acidic it is) Ex: [HEx: [H++]=1.0 X 10]=1.0 X 10-9-9

pH = 9pH = 9 pH is absolute value of exponent for [HpH is absolute value of exponent for [H++]]

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pH scalepH scale What does a logarithmic scale mean?What does a logarithmic scale mean? Each Each ΔΔ in pH # by 1 = in pH # by 1 = ΔΔ in [Hin [H++] or [H] or [H33OO++] ]

by 10by 10

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Powers of 10 videoScale of Universe (powers of 10)

Remember water at 25Remember water at 25ooC!C! [H[H++]= 1.0 X 10]= 1.0 X 10-7 -7 same as [OH-], balancedsame as [OH-], balanced

pH= 7, neutralpH= 7, neutral

Image taken from http://packerpedia.wiki.packer.edu/file/view/pH_Scale.jpg on 8/31/09.

pH sample problemspH sample problemsWhat is the pH in each of the following What is the pH in each of the following

examples?examples?a)a) [H[H++]=1.0 X 10]=1.0 X 10-3-3

pH = 3pH = 3

b)b) [OH[OH--]=1.0 X 10]=1.0 X 10-11-11

KKww=[H=[H++][OH][OH--]] 1.0X101.0X10-14 -14 = [H= [H++][1.0X10][1.0X10-11-11]] 1.0X101.0X10-14-14/1.0X10/1.0X10-11 -11 = [H= [H++]] [H[H++] = 1.0X10] = 1.0X10-3-3

pH=3pH=3

pH sample problemspH sample problemsWhat is the pH in each of the following What is the pH in each of the following

examples?examples?c)c) 0.001M HCl solution0.001M HCl solution

0.001M 0.001M 1.0X10 1.0X10-3-3 = = [H[H++] ] pH=3 pH=3

d)d) 0.01M NaOH solution0.01M NaOH solution 0.01M 0.01M 1.0X10 1.0X10-2-2 = [OH = [OH--] ] KKww = [H = [H++][OH][OH--]] 1.0X101.0X10-14-14 = [H = [H++][1.0X10][1.0X10-2-2]] 1.0X101.0X10-14-14/1.0X10/1.0X10-2-2 = [H = [H++]] [H[H++] = 1.0X10] = 1.0X10-12-12

pH=12 pH=12 basic basic

pOHpOH

pOH = -log [OH-]pOH = -log [OH-]pH + pOH = 14.0pH + pOH = 14.0

Taken from sciencegeek.net on 7/29/11.

BuffersBuffersSolutions used to minimize ( not Solutions used to minimize ( not

prevent) a change in pH when an prevent) a change in pH when an additional acid or base is introduced additional acid or base is introduced into solution.into solution.

Buffers consist of a conjugate pair of a Buffers consist of a conjugate pair of a weak acid and weak base in an weak acid and weak base in an equilibrium system.equilibrium system.

Taken from boughen.com.au on 7/28/11.

Calculating the pH of BuffersCalculating the pH of Buffers

The Henderson-Hasselbalch The Henderson-Hasselbalch equation:equation:

SaltsSalts

An ionic compound containing positive ions other An ionic compound containing positive ions other than H+ and negative ions other than OH-than H+ and negative ions other than OH-

Ionic compound, bonding?Ionic compound, bonding? Ionic bondingIonic bonding

Many salts are strong electrolytes.Many salts are strong electrolytes. Completely dissociate in solution into free ions and Completely dissociate in solution into free ions and

resulting solution will conduct electricity. “Break crystal resulting solution will conduct electricity. “Break crystal lattice.”lattice.”

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5 Methods for Preparing a 5 Methods for Preparing a SaltSalt

1.1. NeutralizationNeutralization

2.2. Single Replacement ReactionSingle Replacement Reaction

3.3. Direct Combination of ElementsDirect Combination of Elements

4.4. Double ReplacementDouble Replacement

5.5. Reaction of a metallic oxide with a nonmetallic oxide.Reaction of a metallic oxide with a nonmetallic oxide.