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

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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