Post on 14-Mar-2020
Acids and Bases
• Acids– Sourtaste– Dissolvemanymetals– Turnlitmuspaperred.– Egs.Ace9cacid(vinegar),
citricacid(lemons)
• Bases– Bi>ertaste,slipperyfeel– Turnlitmuspaperblue.– Egs.Drano,ammonia,caffeine
Arrhenius Definition of Acids and Bases
BasedonH+orOH-Produc9oninWater• Acid:SubstancethatproducesH+ions(protons)inaqueoussolu9ons§ HCl(aq)àH+(aq)+Cl–(aq)
§ HNO3(aq)àH+(aq)+NO3–(aq)
• Base:SubstancethatproducesOH-(hydroxide)ionsaqueoussolu9ons§ NaOH(aq)àNa+(aq)+OH–(aq)
• Defnislimited–restrictedtoreac9onsinwateronly
Bronsted-Lowry Definition of Acids and Bases
BasedonProtonTransfer:• Acids:Protondonors HClàH++Cl-
• Bases:Protonacceptors NH3+H+àNH4
+
Number of Acidic Protons on a Molecule
• Anacidmoleculecanbemonopro9c,dipro9c,ortripro9c(basedonnumberofacidicprotons).
Water Acts as Both Acid and Base (Amphoteric)
• Watercanactasabase,accep9ngaprotonfromanacidàFormshydroniumionH3O+.
• Watercanactasanacid,dona9ngaprotontoabaseàFormshydroxideionOH-
The Proton in Water
• AH+ioninwaterisnotisolated!AH+ioninwatera>ractsthenega9vepoleofwatermoleculesostronglythatitformsacovalentbondtowater.
HCl(aq)+H2O(l)àH3O+(aq)+Cl–(aq) hydroniumion(hydratedproton)
*Alsowri>enas:HCl(aq)àH+(aq)+Cl–(aq)
Bronsted-Lowry Acid and Base Work Together
• Anacidandbasemustalwaysworktogethertotransferaproton!
Inaqueoussolu9onsofacidsorbases,wateractsasthebaseoracid“partner”:
§ HCl+H2OàCl-+H3O+(HClàCl-+H+)
acid base§ NH3+H2OàNH4
++OH-(NH3àNH4++OH-)
baseacid
Acid-Base Reactions Don’t Have to Involve Water
• ABronsted-Lowryacid-basereac9ondoesnotalwaysoccurinwater.
ExProbs
List of Common Acids and Bases
StrongAcids HCl hydrochloricacidHBr hydrobromicacidHI hydroiodicacidHNO3 nitricacid H2SO4 sulfuricacid HClO4 perchloricacid
StrongBases:MetalHydroxidesofGroup1Aca9onsLiOH,NaOH,KOH,etc.andHeavierGroup2Aca9ons:Ca(OH)2,Sr(OH)2,Ba(OH)2
CommonWeakAcids HC2H3O2orCH3COOH ace9cacidH2CO3carbonicacid
CommonWeakBaseNH3ammonia
Conjugate Acid-Base Pair
• NH3andNH4+areaconjugateacid-basepair.
• H2OandOH–areaconjugateacid-basepair.
Conjugateacid-basepair:twosubstanceswhoseformulasdifferbyonlyahydrogenion
Conjugate Acid-Base Pair
• H2SO4andHSO4–areaconjugateacid-base
pair.• H2OandH3O+areaconjugateacid-basepair.
Example Problems
Whichofthefollowingrepresentconjugateacid-basepairs?a. HF,F-b. NH4
+,NH3
c. HCl,H2Od. HClO4,ClO4
-
e. HCl,ClO-
f. H2PO4-,HPO4
2-
g. HNO3,NO3-
✔
✔
✔
✔
✔ExProbs
Acid-Base Reaction: Neutralization
Neutraliza9on:areac9oninwhichanacidandbasereactquan9ta9velywitheachother
Acid-Base Reaction: Acid + Strong Base
Whenanacidandastrongbase(metalhydroxide)react,theyformwaterandasalt(ioniccompound).
• HCl(aq)+NaOH(aq)àH2O(l)+NaCl(aq)
Netioniceqn:H+(aq)+OH-(aq)àH2O(l)
Acid-Base Reaction: Gas-Forming
Whenanacidandabicarbonate(HCO3–)or
carbonate(CO32–)react,waterandgasareformed.
• HCl(aq)+KHCO3(aq)àKCl(aq)+[H2CO3(aq)]à
KCl+H2O(l)+CO2(g)H+(aq)+HCO3
–(aq)à[H2CO3(aq)]àH2O(l)+CO2(g)
• 2HCl(aq)+K2CO3(aq)à2KCl(aq)+[H2CO3(aq)]à 2KCl(aq)+H2O(l)+CO2(g)
2H+(aq)+CO32–(aq)à[H2CO3(aq)]àH2O(l)+CO2(g)
Reaction of Acids with Metals (Redox Rxn)
• Acidsdissolvemanymetals:Acidsoxidizemetals,causingmetalstogointosolu9on.
• 2HCl(aq)+Mg(s)àH2(g)+MgCl2(aq)acid metalH2gassalt
• H2SO4(aq)+Zn(s)àH2(g)+ZnSO4(aq)acid metalH2gassalt
Titration
• Titra9on:Determina9onoftheconcentra9onofasolu9onwithanunknownconcentra9on(analyte)bycombiningitwithastandardsolu9onofknownconcentra9on(9trant).
Acid-Base Titration • Equivalencepoint:thepointwhereenough9tranthasbeenaddedtoreactexactlywiththeanalytepresent
• Indicatorforacid-base9tra9on:Compoundwhosecolorisdifferentinacidthaninbase
• Endpoint:thepointatwhichtheindicator’ssignalistriggered(Theendpointmayormaynotcomeexactlyatequivalencepoint).
moleH+=moleOH–
Acid-Base Titration
• Acid-base9tra9onproblemsarestoichiometryproblems(solu9onstoichiometry).
ExProbs
Acid Strength
• Strongacid:Completelyionized(dissociated).HCl(aq) H+(aq)+Cl-(aq)
• Weakacid:Mostoftheacidmoleculesremainintact.
CH3COOH(aq) H+(aq)+CH3COO-(aq) equilibriumarrow
Strong Acid Solutions
• Strongacidsionizecompletely: HCl à H+ + Cl-
So:0.01MHClà 0.01MH+ + 0.01MCl-
0.5MHClà 0.5MH+ + 0.5MCl-
• Weakacidsdonotionizecompletely:
Acids as Electrolytes
Electrolyte:asolu9onoffreeions,conductselectricity
WeakacidWeakelectrolyte
StrongacidStrongelectrolyte
List of Common Acids and Bases
StrongAcids HCl hydrochloricacidHBr hydrobromicacidHI hydroiodicacidHNO3 nitricacid H2SO4 sulfuricacid HClO4 perchloricacid
StrongBases:MetalHydroxidesofGroup1Aca9onsLiOH,NaOH,KOH,etc.andHeavierGroup2Aca9ons:Ca(OH)2,Sr(OH)2,Ba(OH)2
CommonWeakAcids HC2H3O2orCH3COOH ace9cacidH2CO3carbonicacid
CommonWeakBaseNH3ammonia
Water as an Acid and Base
• Waterisamphoteric:canreactaseitheranacidorbase
• Waterundergoesauto-ioniza9on:H2O(l)+H2O(l)àH3O++OH-
• Forpurewater,25°C:[H3O+]=[OH–]=1.0×10–7M
• Ion-productconstantforwater(Kw)Kw=[H3O+][OH–]=1.0×10–14at25°C *Trueforpurewaterandallaqueoussolu9ons!
Relationship between [H+] and [OH-]
Wecanrelate[H+]and[OH-]throughKw: Kw=[H+][OH–]=1.0x10-14
forwaterandallaqueoussolu9ons
Definitions: Neutral, Acidic, Basic
• Neutralsolu9on:[H+]=[OH–]• Acidicsolu9on:[H+]>[OH–]• Basicsolu9on: [H+]<[OH–]
Ineachcase,however,Kw=[H+][OH–]=1.0×10–14 forwaterandallaqueoussolu9ons
ExProbs
pH Range
pH7 [H+]=[OH-] NeutralpH<7 [H+]>[OH-] AcidicpH>7 [H+]<[OH-] Basic
• LowerthepH,moreacidicthesolu9on.• HigherthepH,morebasicthesolu9on.
Calculating pH and [H+]
• TogetpHfrom[H+]:pH=-log[H+]
• Toget[H+]frompH:pH=-log[H+]-pH=log[H+]Inverselog(-pH)=inverselog(log[H+])Inverselog(-pH)=[H+]OR10-pH=[H+]
ExProbs
Calculating pOH and [OH-]
• TogetpOHfrom[OH-]:pH=-log[OH-]
• Toget[OH-]frompOH:
Inverselog(-pOH)=[OH-]OR10-pOH=[OH-]
ExProbs
Relationship Between pH and pOH
1.0x10-14=[H+][OH–]
log1.0x10-14=log[H+]+log[OH–] -14.00=–log[H+]–log[OH–]
14.00=log[H+]+log[OH–]
14.00=pH+pOH
ExProbs
Equations for pH Calculation Problems
1. pH=-log[H+] (analogousforpOH)2. Invlog[-pH]=[H+](analogousfor[OH–])3. 1.0×10–14=[H+][OH–]4. 14.00=pH+pOH
Exprobs
Buffers
• Buffer:asolu9onthatcontainsbothanacidandabase,thusresistspHchange
• Bufferscontainsignificantamountsofbothaweakacidanditsconjugatebase.
• Theweakacidneutralizesaddedbase. Theconjugatebaseneutralizesaddedacid.
• Eg.ofbuffer:CH3COOHandCH3COO-
(CH3COO-comesfromNaCH3COO)