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TITRIMETRIC TITRIMETRIC ANALYSISANALYSIS
Lecturer: Dr. Hoang Le SonCourse: Analytical ChemistryGroup members:Nguyen Duy Dang BTIU08093Nguyen Thanh Binh BTUN08006Nguyen Duy Han BTUN08013
International University – Vietnam National University
School of Biotechnology
OutlineOutline
IntroductionTerms and definitionsGeneral procedureVolumetric calculationsClassificationApplications
IntroductionIntroduction
Introduction to titrimetric Introduction to titrimetric analysisanalysis
The most useful and accurate analytical technique
Capable of rapid and convenient analyte determinations with high accuracy and precision
Introduction to titrimetric Introduction to titrimetric analysisanalysis
based on the complete reaction between the analyte and a reagent
generic chemical reaction◦aA +tT → products◦A: analyte contained is sample◦T: titrant in titrant solution
TitrationTitration
a standard laboratory method of chemical analysis
used to determine the concentration of unknown reactant
the analyte in a flask reacts with a reagent that is added from a buret as a known concentration solution – standard solution or titrant
The requirements of a titrationThe requirements of a titration
.
Terms and Terms and DefinitionsDefinitions
Terms and DefinitionsTerms and Definitions
Analyte:
Titrant:
Primary Standard Solution: Secondary Standard Solution:
Terms and DefinitionsTerms and Definitions
Equivalent point: .
End point:
Terms and DefinitionsTerms and Definitions
Back titration: a process in which the excess of a standard solution used to consume an analyte is determined by titration with a second standard solution.
Indicators: are often added to the analyte solution to produce an observable physical change ( the end point) at or near the equivalence point.
Primary standard solution & secondary Primary standard solution & secondary standard solutionstandard solution
Primary standard solution◦ ◦ Example:
Sodium Chloride
Secondary standard solution◦
◦ Example:Potassium Permanganate
General procedureGeneral procedure
EquipmentsEquipments
Burette Erlenmeyer flask
Volumetric pipette
Beaker
Stirring rod
FunnelAmber bottle
Graduated cylinder
General stepsGeneral steps
Volumetric Volumetric calculationscalculations
Volumetric calculationsVolumetric calculations
Express the concentration in several ways
Molarity (C), normality (CN) is used◦Molarity: ◦Normality:
Volumetric calculationsVolumetric calculations
Some useful Algebraic relationships: base on 2 pairs of simple equations:
◦nA = mA / MA
nA: amount of A; mA: mass of A; MA: molar mass of A
◦CA = nA / V or nA = V x CA V: volume of solution; CA: molarity of A
Treating dataTreating data
2 types of volumetric calculations
◦Calculating molarities from standardization data
◦Calculating the quantity of analyte from titration data
Calculating molarities from Calculating molarities from standardization datastandardization data
A 50.00mL portion of HCl solution required 29.71ml of 0.01963M Ba(OH)2 to reach an end point with bromocresol green indicator .Calculate the molarity of the HCl.
2 2 2
22
2
2
( ) 2 2
( )( ) 29.71 0.01963 0.583
( )
2(29.71 0.01963) 1.166
1 ( )
(29.71 0.01963 2)0.023328
50.0HCl
Ba OH HCl BaCl H O
mmol Ba OHBa OH ml mmol
mLBa OH
mmolHClHCl mmol
mmolBa OH
C Mml
Calculating the quantity of Calculating the quantity of analyte from titration dataanalyte from titration data
A 100.0ml sample of brackish water was made ammoniacal , and the sulfide it contained was titrated with 16.47 ml of 0.02310M AgNO3. The analytical reaction is
2Ag++S2-→Ag2S(s)
33
3
22
3
322
2
3
2
16.47 0.02310 0.3804
1(16.47 0.02310) 0.1902
2
1(16.47 0.02310 ) 0.034802 6.620 10
2
6.620 10
100.0 1.000
mmolAgNOamountAgNO ml mmol
mLAgNO
mmolH SamountH S mmol
mmolAgNO
gH SmassH S g
mmolH S
gconcH S
gml
6210 6.62ppm ppmH S
ml
ClassificationClassification
Classification of titrimetric Classification of titrimetric analysisanalysis
Acid – Base titrations
Precipitation titrations
Complexometric titrations
Redox titrations
Acid – Base TitrationsAcid – Base Titrations
Acid – base titrationsAcid – base titrations
.
The neutralization reaction
The titrant is always a strong acid or a strong base.
The analyte may be either a strong acid or base or a weak base or acid.
Detection of the end point: Detection of the end point: IndicatorsIndicators
End point An indicator
.
Example: Methyl OrangeHIn H+ + In+
We consider Ka expression for the dissociation of an acid type indicator:
Ka =
lead to [H+] = Ka
At the equivalent point: [HIn] = [In-], then[H+] = Ka ,but we have: pKa=-log(Ka) and pH=-log(H+): pKa = pH
The pKa of the indicator should be close to the pH of the equivalent point.
[H+][In-]
[HIn]
[HIn]
[In-]
Equivalence point, end point, Equivalence point, end point, and indicatorsand indicators
Strong acid – strong baseStrong acid – strong base
The equivalence point pH be 7.00.
Weak acid – strong baseWeak acid – strong base
Weak base – strong acidWeak base – strong acid
Complexometric titrationsComplexometric titrations
Complexometric titrationsComplexometric titrations
Complexometric titrations are useful for the determination of a mixture of different metal ions in solution
The titrant is a complexing agent (chelating agent).
Complexometric titrationsComplexometric titrations
•
•
•
Coordinate covalent bondCoordinate covalent bond
A covalent chemical bond between two atoms that is produced when one atom shares a pair of electrons with another atom
Coordinate covalent bondCoordinate covalent bond
Chelating Agents (ligands)Chelating Agents (ligands)
One of the most common ligands is: Ethylenediaminetetraacetic Acid (EDTA)
Chelating Agents (ligands)Chelating Agents (ligands)
The effect of pH: the pH must be controlled carefully because: ◦ ◦
Chelating Agents (ligands)Chelating Agents (ligands)
+ pH EDTA will influence distribution of: H4Y, H3Y-, H2Y2-, HY3-, Y4-
Complex IonComplex Ion
Comlex Ion of EDTA with metal ions
Indicators in Complexometric Indicators in Complexometric TitrationsTitrations
Common indicator: Eriochrome Black T (EBT)
Eriochrome Black T is blue, but turns red in the presence of metals.
Indicators in Complexometric Indicators in Complexometric TitrationsTitrations
EX: The indicator (EBT) can be used for the titration of Mg2+ with EDTA
MgIn- + H2Y2- MgY2- + HIn2- + H+
(Red) (Blue)
Types of Complexometric Types of Complexometric TitrationsTitrations
Direct Titration
Back Titration
Replacement Titration
Indirect Titration
Types of Complexometric Types of Complexometric TitrationsTitrations
Direct Titration: ◦ It is the simplest and the most convenient
method is used.
◦ ◦ Limitations :
Ex: titration of Mg2+ with EDTA+ The indicator is used is EBT+ Mg(II)-EBT complex is formed+ Addition of EDTA displaces
ammonia with corresponding color change
MgIn- + H2Y2- MgY2- + HIn2- + H+
(Red) (Blue)
Types of Complexometric Types of Complexometric TitrationsTitrations
Back Titration: ◦
◦
◦ Ex: Determination of Mn:
◦ Mn can not be directly titrated with EDTA.
Types of Complexometric Types of Complexometric TitrationsTitrations
◦ An excess of EDTA is added to an solution of Mn salt
◦ EDTA + Mn2+ Mn-EDTA
◦ Then the excess EDTA is back titrated with a standard Mg solution kept in burette using Eriochrome blackT as indicator
◦ excess EDTA + Mg2+ Mg-EDTA
Types of Complexometric Types of Complexometric TitrationsTitrations
Replacement Titration◦
◦ Ex: Determination of M metal by Mg-EDTA-2
M + Mg-EDTA-2 Mg+2 + M-EDTA-2
◦ The Mg+2 is then directly titrated with a standard EDTA solution
Types of Complexometric Types of Complexometric TitrationsTitrations
Indirect Titration◦
◦ Ex: determination of SO42-
SO42- + excess Ba2+ BaSO4
◦ The precipitate (BaSO4) and boil with excess EDTA Ba(EDTA)2-
◦ Using excess EDTA is back titration with Mg2+
Application: Application: determination water determination water hardness by Complexometric Titrationhardness by Complexometric Titration
What is hard water?◦ Metal ions (minerals)
include Ca2+, Mg2+, Fe3+, SO42-, and HCO3- that are dissolved in the ground water.
◦ Hard water does cause soap scum, clog pipes and clog boilers.
Application: Application: determination water determination water hardness by Complexometric Titrationhardness by Complexometric Titration
The EDTA solution is titrantThe indicator is Eriochrome Black T
(EBT)
The hardness of watter
Application: Application: determination water determination water hardness by Complexometric hardness by Complexometric TitrationTitration
Redox titrationsRedox titrations
Redox titrationsRedox titrations
Definition
Redox indicator
Half reaction
Titration involving Iodine
Common Redox reagents
DefinitionDefinition
.
Ared + Tox Tred + Aox
Ared: the analyte in a reduced state
Tox: the titrant in an oxidized state
The end point can be determined by a visual indicator.
Oxidation - reduction reaction: ◦
Examples:
Redox titrationsRedox titrationsNernst equation:
◦ Simple equation: aOx + ne- bRed
◦ E: redox potential at specific concentrations (V)
◦ E0: standard potential (equivalent point potential)
◦ R: Constant of gas (8,311 J)◦ T: Absolute temperature◦ F: Faraday constant (96500c)◦ n: number of changed e
aox
d
AredA
nF
RTEE ln0
IndicatorsIndicators
Redox indicators undergo a definite color change at a specific electron potential
There are two types:◦ Metal-organic complexes (ex. Phenanthroline)◦ True organic redox systems (ex. Methylene
blue)
You can control indicators using factors like pH
pH independent Redox pH independent Redox IndicatorsIndicators
pH dependent Redox IndicatorspH dependent Redox Indicators
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