Download pdf - Chemistry 12 Acid-Base Equilibrium VII• A graph that plots the pH of the solution vs. the volume of the titrant added. ... • Calculate pH of the solution resulting from the anionic

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Page 1: Chemistry 12 Acid-Base Equilibrium VII• A graph that plots the pH of the solution vs. the volume of the titrant added. ... • Calculate pH of the solution resulting from the anionic

Chemistry12Acid-BaseEquilibriumVII

Name:Date:Block:

1. Titrations2. Indicators

TitrationsTitrationisaformofvolumetricanalysiswherethenumberofmolesofsoluteinasolutionisdeterminedbyaddingasufficientvolumeofanothersolutionofknownconcentrationtojustproduceacompletereaction.

• ThereactioniscompletedwhenthenumberofmolesofH3O+equalsthetotalnumberofmolesofOH--thisiscalledtheequivalencepointorstoichiometricpointofthetitration.

• AnindicatorisusedthatwillindicatewhentheequivalencepointhasbeenreachedbychangingcolouratorverynearthepHassociatedwiththeequivalencepoint.

Wewillbedealingwith3scenarios:1.2.3.

(Chemistry11)Example1:AstudentstandardizingasolutionofNaOHfindsthat28.15mLofthatsolutionisrequiredtoneutralize25.00mLofa0.1072MstandardsolutionofHCl.Calculatethe[NaOH].

• Writethebalancedequation.

• WhatistheconcentrationofNaOH?

Page 2: Chemistry 12 Acid-Base Equilibrium VII• A graph that plots the pH of the solution vs. the volume of the titrant added. ... • Calculate pH of the solution resulting from the anionic

Example2:A20.0mLsampleof0.450MHNO2istitratedwitha0.500MNaOHsolution.Whatvolumeofbaseisaddedatexactlyhalfwaytotheequivalencepoint?

• Drawasketchoftheset-up:

• Whatisthebalancedreaction?

• WhatvolumeofNaOHwasneededatequivalencepoint?

• Whatishalfwaytoequivalencepoint?

TITRATIONCURVES:• AgraphthatplotsthepHofthesolutionvs.thevolumeofthetitrantadded.

Asthetitrantisadded,thepHisgradually(increasing/decreasing)whichmeansthat(acid/base)isthetitrant.HowmanymLoftitrantwasrequiredtoattainequivalencepoint?___________LookingattheequivalencepointpH,doyouthinkthereactionproducedanacidicorbasicsalt?

Whatdoyouthinkthegraphwouldlooklikeifanacidwasthetitrant?Explainyouranswer.

Page 3: Chemistry 12 Acid-Base Equilibrium VII• A graph that plots the pH of the solution vs. the volume of the titrant added. ... • Calculate pH of the solution resulting from the anionic

1.StrongAcid&StrongBase

HCl(aq)+NaOH(aq)àNaCl(aq)+H2O(l)

• Typicalstrongacid+strongbaseneutralizationtypeofquestion.(1)Dilution(2)Neutralization(3)Acidicorbasic?

2.WeakAcid&StrongBase

CH3COOH(aq)+NaOH(aq)àNaCH3COO(aq)+H2O(l)

50.0mLof0.100Maceticacidistitratedwith0.150MNaOH.WhatdoyouthinkthepHcurvewilllooklike?

BecausethepHmeterismeasuringfromthebeaker,wealwayshavetothinkabout__________________!

Wewillbecalculating(andcomparing)thepHat4pointsonthecurve:1. 2. 3. 4.

CalculatethepHofthesolutionproducedinthereactionflaskatthefollowingpoints:1) ThepHofthesolutionofaceticacidwhennoNaOHisyetadded.

• Thisisaweakacidcalculation.

Page 4: Chemistry 12 Acid-Base Equilibrium VII• A graph that plots the pH of the solution vs. the volume of the titrant added. ... • Calculate pH of the solution resulting from the anionic

2) When10.0mLof0.150MNaOHhasbeenadded.

• Actsverysimilarlytoabufferastheaddedhydroxideionsreactswithaceticacidtoproduceacetateions.

• Whatarethedilutedconcentrationsofreactantacidandbasebeforethereaction(initialconcentrations)?

• CreateanICEtable.

• CH3COOHandCH3COO-createsanacidbuffer.

• CalculatethepH.

Page 5: Chemistry 12 Acid-Base Equilibrium VII• A graph that plots the pH of the solution vs. the volume of the titrant added. ... • Calculate pH of the solution resulting from the anionic

3) Attheequivalencepointwhen______mLofNaOHhasbeenadded.

• WhatvolumeofNaOHisneededatequivalencepoint?

• Whatarethedilutedconcentrationsofreactantacidandbasebeforethereaction(initialconcentrations)?

• CreateanICEtable.

• Theanionofthedissociatedsalt,NaCH3COO,istheconjugatebaseofaweakacidandisthuscapableofacceptingprotonsfromwaterinahydrolysisreaction.

• Whatisthehydrolysisreaction?

• CreateanICEtable.

• CalculatepHofthesolutionresultingfromtheanionichydrolysisoftheacetateion.

Page 6: Chemistry 12 Acid-Base Equilibrium VII• A graph that plots the pH of the solution vs. the volume of the titrant added. ... • Calculate pH of the solution resulting from the anionic

4) Beyondtheequivalencepointwhen60.0mLofNaOHadded

Page 7: Chemistry 12 Acid-Base Equilibrium VII• A graph that plots the pH of the solution vs. the volume of the titrant added. ... • Calculate pH of the solution resulting from the anionic

Practice:A20.0mLsampleof0.450MHNO2istitratedwitha0.500MNaOHsolution.WhatwillthepHbeinthereactionflaskatthefollowingpoints:

a) 2.0mLbeforeexactlyhalfwaytotheequivalencepoint?

Page 8: Chemistry 12 Acid-Base Equilibrium VII• A graph that plots the pH of the solution vs. the volume of the titrant added. ... • Calculate pH of the solution resulting from the anionic

b) Atequivalencepoint?

Page 9: Chemistry 12 Acid-Base Equilibrium VII• A graph that plots the pH of the solution vs. the volume of the titrant added. ... • Calculate pH of the solution resulting from the anionic

3.StrongAcid&WeakBase

NH3(aq)+HCl(aq)àNH4+(aq)+Cl-(aq)100.0mLof0.050MNH3istitratedwith0.10MHCl.CalculatethepHofthesolutionproducedinthereactionflaskatthefollowingpoints:

1) BeforeanyHClisadded.2) Atthemidpointofthetitration.

Page 10: Chemistry 12 Acid-Base Equilibrium VII• A graph that plots the pH of the solution vs. the volume of the titrant added. ... • Calculate pH of the solution resulting from the anionic

3) Attheequivalencepointwhen_______mLofHClhasbeenadded.

Page 11: Chemistry 12 Acid-Base Equilibrium VII• A graph that plots the pH of the solution vs. the volume of the titrant added. ... • Calculate pH of the solution resulting from the anionic

4) When60.0mLofHClhasbeenadded.

Page 12: Chemistry 12 Acid-Base Equilibrium VII• A graph that plots the pH of the solution vs. the volume of the titrant added. ... • Calculate pH of the solution resulting from the anionic

Practice:CalculatethepHofthesolutionproducedinthereactionflaskwhen13.00mLof0.100MHClO4hasbeenaddedto25.00mLof0.100MNaNO2.(Thisisjustbeyondhalfwaytotheequivalencepoint.)

Page 13: Chemistry 12 Acid-Base Equilibrium VII• A graph that plots the pH of the solution vs. the volume of the titrant added. ... • Calculate pH of the solution resulting from the anionic

IndicatorsWemeasurepHusingeitheranacid-baseindicatororapHmeter.Acid-baseindicatorsareweakorganicacidswhoseconjugatepairsdisplaydifferentandnormallyintensecolours.Acid-baseindicatorsarecomplexorganicmoleculesandrefertothemassimply“HIn.”

HIn+H2O⇋In-+H3O+

Ka=Example:Considermethylredindicator.

pH:Colour:

• ThepHvalueatwhichtheindicatorexhibitsacolourchangeshouldbeclosetothepHatequivalencepoint.(____________à____________ß____________).

• Whenthecolourchanges,(reached_______________________point)itisanindicationthatthetitrationhasreachedequivalencepoint.

pHatequivalence

point[H3O+] Indicator Colourexhibited

Alizarinyellow

6.8

Lightpink

Thymolblue Green

2.0

Page 14: Chemistry 12 Acid-Base Equilibrium VII• A graph that plots the pH of the solution vs. the volume of the titrant added. ... • Calculate pH of the solution resulting from the anionic

When1.0MNH3istitratedwith1.0MHCl,themostsuitableindicatoris:

A.methylviolet. C.phenolphthalein. B.indigocarmine. D.bromcresolgreen.

Themostappropriateindicatorforthetitrationof0.50MCH3COOHwith0.50MNaOHis

A.methylviolet. C.phenolphthalein. B.indigocarmine. D.bromcresolgreen.

HebdenWorkbookPg.162#108-116


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