1. Titrimetry

2. Titration is an analytical method that uses accurate and precise volume delivery of one solution of known concentration to determine the concentration of another solution through a monitored reaction.

3. Titration is an analytical method that uses accurate and precise volume delivery of one solution of known concentration to determine the concentration of another solution through a monitored reaction.

4. There are three essential parts of a titration experiment: (1) Titrant, (2) Analyte, (3) Indicator
Titrant – solution of known concentration which is accurately delivered using a buret
Analyte – solution of unknown concentration which reacts with the titrant
Indicators – compounds which do not participate in the general reaction between analyte and titrant, but are indirectly affected by the reaction producing notable changes. They are used to monitor the reaction.
Some reactions also produce self-indicators.

5. End point ≠ Equivalence Point Indicator error
The goal of titration is be able to deliver a stoichiometrically equivalent amount of titrant to an analyte solution
Equivalence point – is reached when the quantity of titrant added is the exact amount necessary for reaction with analyte
End point – is marked by a sudden change in a physical property of the solution
End point ≠ Equivalence Point
Indicator error
End point ≈ Equivalence Point
(use of blank titration)

6. The goal of titration is be able to deliver a stoichiometrically equivalent amount of titrant to an analyte solution
Example I have 5 mmol oxalic acid reacts with 2 moles of permanganate

7. How does one design a titration experiment?
The reaction of the titrant and analyte must proceed according to a definite chemical equation
The reaction should proceed to completion at the equivalence point
Some method must be available to determine equivalence point
Indicators
Electrochemical monitoring
Must be rapid
Example I have 5 mmol oxalic acid reacts with 2 moles of permanganate

8. There are several types of titration according to the reactions of the analyte
Acid-Base Neutralization reaction – utilizes the reactions of acids with bases. Reaction is monitored using pH changes.
Ex: CH3COOH + NaOH  CH3COO- + H2O + Na+
Precipitation Titration – forms insoluble salts which also serves as a monitor of reaction completion.
Ex: Volhard Methods and Fajans Method
RedOx Titrations – involves species which undergo redox reactions. The reaction is monitored by RedOx indicators or thru Electrochemical methods.
Ex: 2 MnO C2O H+  2 Mn CO2 + 8 H2O
Complexometric Titrations – reactions involving chelating/complexing agents.
Ex. EDTA titrations and Leibig Method

9. The concentration of the titrant must be known to a high accuracy in order for the results to be useful
Standardization – is the process by which the concentration of titrant is determined to a high degree of accuracy.
Primary standards are highly purified compounds that serve as REFERENCE MATERIAL for all titrimetric methods
Must satisfy most, if not all, of the criteria listed:
High purity
High air stability
Non-hygroscopic
Readily available at modest cost
Highly soluble
Large molar mass

10. The concentration of the titrant must be known to a high accuracy in order for the results to be useful
Standardization – is the process by which the concentration of titrant is determined to a high degree of accuracy.
Secondary standards are compounds whose purity is established by chemical analysis using primary standards.
Must satisfy most, if not all, of the criteria listed:
High purity
High air stability
Non-hygroscopic
Readily available at modest cost
Highly soluble
Large molar mass

11. There are two ways of performing a titration experiment
Analyte
Titrant
DIRECT TITRATION +
Until equivalence is reached
Analyte
Titrant 1
Excess Titrant 1
Titrant 2 + +
Until equivalence is reached
BACK TITRATION

12. Precipitation Titration

13. Precipitation titration involves the formation of insoluble salts.
RECALL: Factors affecting solubility
Temperature
Solvent
Common-ion effect
Activity/Ionic strength pH
Complexation

14. Common methods involve silver ion (Ag+) and are called ARGENTOMETRIC TITRATIONS
Volhard titration – involves the formation of a soluble, colored complex at the end point
Add an excess of standard AgNO3
Solid AgCl is removed
Analyte
(ex. Cl-) +
Excess
Ag+
Titrate with KSCN with Fe3+ as indicator
Ag+ + SCN-  AgSCN (s)
After all Ag+ is exhausted…
Fe3+ + SCN-  FeSCN2+ (aq)
(RED SOLUTION) +

15. Common methods involve silver ion (Ag+) and are called ARGENTOMETRIC TITRATIONS
Species Analyzed
Notes
VOLHARD METHOD
Br-, I-, SCN-, CNO-, AsO43-
Precipitate removal is unnecessary
Cl-, PO43-, CN-, C2O42-, CO32-, S2-, CrO42-
Precipitate removal is required

16. Common methods involve silver ion (Ag+) and are called ARGENTOMETRIC TITRATIONS
Fajans titration – involves the adsorption of a colored indicator on the precipitate at the end point.
In 2-
Ag+ + Cl-  AgCl (s) + + + - - + - + - + - - + - + - + - + - + - + - + - + - + - - + - + - + - + - + - + -
In 2- - - - + - + - + +

17. Common methods involve silver ion (Ag+) and are called ARGENTOMETRIC TITRATIONS

18. Common methods involve silver ion (Ag+) and are called ARGENTOMETRIC TITRATIONS
Species
Titrant
Indicator
FAJANS
Cl-, Br-, I-, SCN-, Fe(CN)64-
Ag+
Fluoresceine, Dichlorofluorescein, eosin, bromophenol blue F-
Th(NO3)4 to produce ThF4
Alizarin Red S
Zn2+
K4Fe(CN)6 to produce K2Zn3[Fe(CN)6]2
Diphenylamine
SO42-
Ba(OH)2 in 50% v/v MeOH
Hg22+
NaCl to produce Hg2Cl2
Bromophenol blue
PO43-, C2O42-
Pb(Ac)2 to give Pb3(PO4)2 and PbC2O4.
Dibromofluorescein or fluorescein

19. EXAMPLES
A Fajans titration of a g sample required mL of M AgNO3. What is the %Cl of the sample?
The bismuth in g of an alloy was precipitated as BiOCl and separated from the solution by filtration. The washed precipitate was dissolved in nitric acid to convert all chlorine to Cl-. This was then treated with mL of M AgNO3, causing the precipitation of AgCl. The excess AgNO3 required mL of M KSCN for titration. Calculate % Bi in the sample

20. Acid-Base Titrations

21. change occurs over ~2 pH units
Acid-base indicators are usually weak acids (HIn) which have different color than its conjugate base (In-).
basic
change occurs over ~2 pH units
acidic

22. Acid-base indicators are usually weak acids (HIn) which have different color than its conjugate base (In-).