Chemistry 12 Acid-Base Equilibrium VII
Transcript of Chemistry 12 Acid-Base Equilibrium VII
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.