1. Acid- Base Titration.ppt

Titrated

2. Acid-BaseTitration
•Titrationisaprocedurefordeterminingthevolumeoftwosolution(acid&
base)whichwillexactlyneutralizeoneanother.Byusingasolutionofknown
concentration,(standardsolution)theconcentrationofanothersolutioncan
bedetermined.
•Anacid-basetitrationisaprocedureusedinquantitativechemicalanalysis
todeterminetheconcentrationofeitheracidorabase.
•Theequivalenceofanacid-basetitrationisthepointatwhichthereare
equalamounts(inmoles)ofH3O+andOH-intitrationflask.

3. •Endpointoftitration–thepointinatitrationatwhichtheindicator
changescolour.
•Theindicatorshouldchangecoloursharplyattheequivalencepoint.
•Attheendpointofthetitration,
•alltheacidhasbeenneutralizedbythealkali
•thesolutionintheconicalflaskcontainsaltandwateronly.
Fig.: Titrationapparatus
titrant
analyte

4. •Indicatorisasubstancethatisgenerallyaddedtothesolutioninthe
receivingvesselwhichundergoessomesortofcolorchangewhen
reactionisover.
•Acidbaseindicatorsareweakorganicacidsthatdissociateslightly
inaqueoussolutionstoformions.
•Theindicatorscanchangecolorbecausetheirionshavecolorsthat
aredifferentfromundissociatedmolecule.
Acid-BaseIndicators

5. Qualitative chemicalanalysis:
Determine the chemical compositionin a sample using chemical reactions and
interactions.
Example:Test for halideswith Beilstein test(green flame ifhalides are
present).
Quantitative chemical analysis:
Determine the content in a sample of one or more chemical substances using
chemical reactions and interactions.
Example: Vitamin C content in orange juice by titration.
Sample:
A small representative portion of the entity that should be analyzed.
Example: Orange juice

6. Analyte:
Thechemicalsubstancetobedeterminedwiththeanalysis.
Example:VitaminC.
Matrix:
Everythinginthesamplebesidestheanalyte(s).
Example:Water,pulp,sugar,...invitaminCanalysisoforangejuice.
Titrant:
Solutionofknownconcentrationwhichisaddedtothesample(titration)
andreactswiththeanalyte.Theanalytecontentiscalculatedfromthe
consumptionofthetitrant.

7. Acid-base reactionsExample
Strong acid withstrong base HCl and NaOH
Strong acid withweak base HCl and NH3
Weak acid withstrong base CH3COOH and NaOH
Weak acid withweak base CH3COOH and NH3

8. Indicator pH range
Colour change
Acid Alkali
Methyl orange 3.2-4.2 Red Yellow
Bromothymol blue 6.0-7.6 Yellow Blue
Phenolphtalein 8.2-10.0 Colorless Pink

9. Acid Base pH at equivalence
point
Indicators
Strong Strong = 7 (neutral)Methyl orange
Phenolphthalein
Strong Weak < 7 (acidic) Methyl orange
Weak Strong > 7 (basic) Phenolphthalein
Weak Weak pH depend on K
a and
K
b of acid & base
conc.
-

10. AtitrationcurveisaplotofpHvs.theamountoftitrantadded.Typically
thetitrantisastrong(completely)dissociatedacidorbase.Suchcurves
areusefulfordeterminingendpointsanddissociationconstantsofweak
acidsorbases.

11. H
2O
(l) + NaCl
(aq)
Base at the
end of the
titration
Acidic at the
start of the
titration
The titration curve for strong acid-strong basetitration

12. 1.ThepHstartsoutlow,reflectingthehigh[H3O+]ofthestrongacid
andincreasesgraduallyasacidisneutralizedbytheaddedbase.
2.SuddenlythepHrisessteeply.Thisoccursintheimmediatevicinityof
theequivalencepoint.ForthistypeoftitrationthepHis7.0atthe
equivalencepoint.
3.Beyondthissteepportion,thepHincreasesslowlyasmorebaseis
added.

13. CH
3COONa
(aq) + H
2O
(l)
At
equivalenc
e point (pH
>7):
The titration curve for weak acid-strong base titration

14. 1.TheinitialpHishigher.
2.Agraduallyrisingportionofthecurve,calledthebufferregion,
appearsbeforethesteeprisetotheequivalencepoint.
3.ThepHattheequivalencepointisgreaterthan7.00.
4.Thesteepriseintervalislesspronounced.

15. NH4Cl(aq)
At
equivalence
point (pH <
7):
NH
4+ +(aq)+ H2O(l) NH3(aq)+ H(aq)
The titration curve for strong acid-weak base titration

16. 1.TheinitialpHisabove7.00.
2.Agraduallydecreasingportionofthecurve,calledthebufferregion,
appearsbeforeasteepfalltotheequivalencepoint.
3.ThepHattheequivalencepointislessthan7.00.
4.Thereafter,thepHdecreasesslowlyasexcessstrongacidisadded.

17. Types of TitrationsEnd Point pH RangeSuitable Indicators
Strong Acid-Strong Base 3 –10 Any Indicator
Weak Acid-Strong Base 7 –11 Phenolphthalein,
thymol blue
Strong Acid-weak Base 3 –7 Methyl orange, methyl
red
Weak Acid-Weak Base - -
Choosing a SuitableIndicator
•Choose an indicator which the end point pH range lies on the steep part of the
titration curve.
•This choice ensures that the pH at the equivalent point will fall within the
range over which indicator changes color
Table: pH Ranges for Indicator

18. What is the colour of the solution when 3 drops of the below
indicators are added separately to water (pH = 7) ?
Indicator pH range colour change
Phenolphthalein8.2 –10.0 Colourlessreddish pink
Methyl orange 3.2 –4.2 RedYellow
Bromothymol
blue
6.0 –7.6 YellowBlue
phenol red 6.8 –8.4 Yellowred

19. Titrationisananalyticalmethodwhichiswidelyusedinmanydifferent
segmentsandformanydifferentsamples.
Chemicalindustry:Watercontentinsolvents,acidvalueinresinsand
polymers,hydroxylvalueinpolyols,surfactantcontentinrawmaterials,
…
Foodandbeverage:AcidandvitaminCcontentinfruitjuices,chloride
contentinspicysauces,nitritecontentinfoodproducts.
Electroplating:Nickelcontentinelectrolessbath,goldandsilver
contentinalloys,chromiumcontentinelectroplatingbaths,…
Application

20. •Pharmaceutical:Watercontentsinrawproducts,chondroitinsulfate
sodiumintablets,purityandcontentofdifferentactivepharmaceutical
ingredientslikebenzylnicotinate,clotrimazolanddiclofenacsodium.
•Petrochemical:Acidandbasenumberinoils,mercaptanesulfur
contentinkerosene,chloridecontentinmotoroil.
•Environmental:Totalhardnessofwater,coppercontentinaqueous
solution,residualchlorineinbleach,fluoridecontentinwater.
Application