Chemistry12Acid-BaseEquilibriumVII

Name:Date:Block:

1. Titrations2. Indicators

TitrationsWarmup…1.Balancethefollowingneutralizationequation:

_____H2SO4+_____NaOHà_____H2O+_____Na2SO4

2.WritetheformulasfortheacidandbasethatwillreacttogiveK2CO3andwater.

Thesaltbreaksuptobecome:Acid: Base:

Acid-BaseTitration:

• Amethodtodeterminethe__________________concentrationofasolutionbyreactingitwithanothersubstanceof______________concentration.

• Thesolutionwhoseconcentrationisknowniscalledthe_______________________________solution.

• Thegeneralsetup:

ü Makesuretoreadthebottomofthemeniscus

ü Takedatafromat

least_______trials.ü Yourvaluesfromeach

trialshouldbeclosetogether(+/-0.50mL).Iftheyarenot,takeanotherreadingtodoublecheck!

TheequivalencepointpHisfoundonthesteepestpointinthecurve.Indicatetheequivalencepointonthecurve

above.

WhatisthepH?_________

Whatvolumeoftitrantwasneeded?_________

AvarietyofindicatorsareavailabletoindicatethataparticularpHhasbeenreached.Whatindicatorwouldbemostappropriateforthetitration?_________________________

Whatcolourwouldyouexpecttosee?______________

Whenthecolourchangeoccurs,thetitrationhasreachedtheendpoint.Whenthemolof_______________________andmolof_______________________arestoichiometricallyequal,youhavereachedequivalencepoint!Example1.

Astudentcompletelytitrated10.0mLofHClwith18.25mLof0.100MNaOH.Calculatethe[HCl].Þ Balancedequation:

Þ [HCl]=

Practice1:If46.2mLof2.50MNaOHisrequiredtoneutralize1.54Mofaphosphoricacidsolution,H3PO4,whatvolumeofphosphoricacidwasneededtoreachtheequivalencepoint?

Practice2:If8.60mLof0.0994MHNO3isrequiredtoneutralize25.00mLofastrontiumhydroxidesolution,whatisthemolarityofthestrontiumhydroxide?

Practice3:Calculatethemolarityofanaceticacidsolution(CH3COOH)if34.57mLofthissolutionareneededtoneutralize25.19mLof0.1025Msodiumhydroxide.Practice4:25.0mLofcitricacidistitratedwithsodiumhydroxideandproducesthefollowingreaction.

_____C3H5O(COOH)3(aq)+_____NaOH(aq)à_____Na3C3H5O(COO)3(aq)+_____H2O(l)If5.12mLof0.500MNaOHisneededforthetitration,whatistheconcentrationoftheacid?

Practice5:Considerthefollowingresultsfromatitrationlab.

5.00gofNaOHwasdissolvedtomakea200.mLsolutionBelowisthevolumeoftheNaOHsolutionneededtoneutralize25.0mLH3PO4.

Trial#1 Trial#2 Trial#3

Initialreadingofburette

(mL)0.00 12.45 24.94

Finalreadingofburette(mL) 12.45 24.94 37.36

a) Whatisthebalancedequation?

b) Whatistheconcentrationofthestandardizedsolution?

c) Whatistheaveragevolumeofthestandardizedsolutionused?

d) Whatistheconcentrationoftheacid?

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

HIn+H2O⇋In-+H3O+

Ka=Example:Considermethylredindicator.

pH:Colour:

• ThepHvalueatwhichtheindicatorexhibitsacolourchangeshouldbeclosetothepHatequivalencepoint.(____________à____________ß____________).

• Whenthecolourchanges,(reached_______________________point)itisanindicationthatthetitrationhasreachedequivalencepoint.

pHatequivalence

pointIndicator Colourexhibited

Alizarinyellow

6.8

Lightpink

Thymolblue Green

2.0

Practice1.Whatwouldbeasuitableindicatorforthefollowing?

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

50.0mLof0.100Maceticacidistitratedwith0.150MNaOH.

Practice2.A20.0mLsampleof0.450MHNO2istitratedwitha0.500MNaOHsolution.Whatindicatorwouldbesuitableforthistitration?

Practice3.When1.0MNH3istitratedwith1.0MHCl,themostsuitableindicatoris:

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

Practice4.Themostappropriateindicatorforthetitrationof0.50MCH3COOHwith0.50MNaOHis

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

HebdenWorkbookPg.162#108–112,117,118