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TITRIMETRIC TITRIMETRIC ANALYSIS ANALYSIS Lecturer: Dr. Hoang Le Son Course: Analytical Chemistry Group members: Nguyen Duy Dang BTIU08093 Nguyen Thanh Binh BTUN08006 Nguyen Duy Han BTUN08013 International University – Vietnam National University School of Biotechnology

TITRIMETRIC ANALYSIS12

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Page 1: TITRIMETRIC ANALYSIS12

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

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OutlineOutline

IntroductionTerms and definitionsGeneral procedureVolumetric calculationsClassificationApplications

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IntroductionIntroduction

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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

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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

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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

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The requirements of a titrationThe requirements of a titration

.

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Terms and Terms and DefinitionsDefinitions

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Terms and DefinitionsTerms and Definitions

Analyte:

Titrant:

Primary Standard Solution: Secondary Standard Solution:

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Terms and DefinitionsTerms and Definitions

Equivalent point: .

End point:

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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.

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Primary standard solution & secondary Primary standard solution & secondary standard solutionstandard solution

Primary standard solution◦ ◦ Example:

Sodium Chloride

Secondary standard solution◦

◦ Example:Potassium Permanganate

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General procedureGeneral procedure

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EquipmentsEquipments

Burette Erlenmeyer flask

Volumetric pipette

Beaker

Stirring rod

FunnelAmber bottle

Graduated cylinder

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General stepsGeneral steps

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Volumetric Volumetric calculationscalculations

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Volumetric calculationsVolumetric calculations

Express the concentration in several ways

Molarity (C), normality (CN) is used◦Molarity: ◦Normality:

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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

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Treating dataTreating data

2 types of volumetric calculations

◦Calculating molarities from standardization data

◦Calculating the quantity of analyte from titration data

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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

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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

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ClassificationClassification

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Classification of titrimetric Classification of titrimetric analysisanalysis

Acid – Base titrations

Precipitation titrations

Complexometric titrations

Redox titrations

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Acid – Base TitrationsAcid – Base Titrations

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Acid – base titrationsAcid – base titrations

.

The neutralization reaction

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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.

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Detection of the end point: Detection of the end point: IndicatorsIndicators

End point An indicator

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.

Example: Methyl OrangeHIn H+ + In+

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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-]

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Equivalence point, end point, Equivalence point, end point, and indicatorsand indicators

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Strong acid – strong baseStrong acid – strong base

The equivalence point pH be 7.00.

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Weak acid – strong baseWeak acid – strong base

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Weak base – strong acidWeak base – strong acid

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Complexometric titrationsComplexometric titrations

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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).

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Complexometric titrationsComplexometric titrations

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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

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Coordinate covalent bondCoordinate covalent bond

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Chelating Agents (ligands)Chelating Agents (ligands)

One of the most common ligands is: Ethylenediaminetetraacetic Acid (EDTA)

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Chelating Agents (ligands)Chelating Agents (ligands)

The effect of pH: the pH must be controlled carefully because: ◦ ◦

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Chelating Agents (ligands)Chelating Agents (ligands)

+ pH EDTA will influence distribution of: H4Y, H3Y-, H2Y2-, HY3-, Y4-

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Complex IonComplex Ion

Comlex Ion of EDTA with metal ions

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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.

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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)

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Types of Complexometric Types of Complexometric TitrationsTitrations

Direct Titration

Back Titration

Replacement Titration

Indirect Titration

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Types of Complexometric Types of Complexometric TitrationsTitrations

Direct Titration: ◦ It is the simplest and the most convenient

method is used.

◦ ◦ Limitations :

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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)

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Types of Complexometric Types of Complexometric TitrationsTitrations

Back Titration: ◦

◦ Ex: Determination of Mn:

◦ Mn can not be directly titrated with EDTA.

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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

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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

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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+

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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.

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Application: Application: determination water determination water hardness by Complexometric Titrationhardness by Complexometric Titration

The EDTA solution is titrantThe indicator is Eriochrome Black T

(EBT)

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The hardness of watter

Application: Application: determination water determination water hardness by Complexometric hardness by Complexometric TitrationTitration

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Redox titrationsRedox titrations

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Redox titrationsRedox titrations

Definition

Redox indicator

Half reaction

Titration involving Iodine

Common Redox reagents

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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.

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Oxidation - reduction reaction: ◦

Examples:

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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

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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

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pH independent Redox pH independent Redox IndicatorsIndicators

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pH dependent Redox IndicatorspH dependent Redox Indicators

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THANKS FOR THANKS FOR YOUR LISTENINGYOUR LISTENING