PHA6116 LAB: UNIT #1.4-1.5: TITRATION AND TITRIMETRIC METHODS OF ANALYSIS

TITRATION

Those analytical methods which the volume of a solution of known concentration consumed during an analysis is taken as a measure of the amount of active constituent in a sample being analyzed

TITRANT

A solution of known concentration

ANALYTE

A substance being analyzed

STANDARD

Used to prepare a standard solution

STANDARD

A solution of known concentration

INDICATOR

• A chemical that changes color at or very near the equivalence point 

END POINT

Physical change

EQUIVALENCE POINT

Where equivalent quantities of analyte and titrant have reacted

For assay procedure

Acid-Base Titration

standardization procedure

Phenolphthalein Indicator

acidic

Red

basic

Yellow

Neutral endpoint

Peach/salmon

TITRIMETRIC METHODS OF ANALYSIS

Based upon measuring the amount of reagent of known concentration (T) - titrant that is consumed by the analyte (A)

TITRIMETRIC METHODS OF ANALYSIS

Widely used for routine analyses because they are rapid, convenient, accurate and readily automated

VOLUMETRIC TITRIMETRY

Performed by slowly adding a standard solution from a burette to a solution of the analyte until the reaction between the two is judged complete

difference

Volume of reagent needed to complete the titration is determined from the _ between the initial and final volume readings

EQUIVALENCE POINT

amount T = amount A

END POINT

A physical change associated with the condition of chemical equivalence occurs during titration

INDICATOR

Often added to the analyte solution in order to give an observable physical change (the end point) at or near the equivalence point

INDICATOR

• Typical indicator changes: 

  • Appearance/disappearance of color,

  • A change in color, 

  • Appearance/disappearance of turbidity

INDICATOR

Weaker than the analyte, kept at a minimum amount, intensely colored and react last with the titrant

INSTRUMENTS TO DETECT END POINTS

• Voltmeters

• Ammeters

• Ohmmeters

• Colorimeters 

• Temperature recorders and 

• Refractometers

PRIMARY STANDARD

A highly purified compound that serves as a reference material in all volumetric methods

PRIMARY STANDARD

Accuracy of a method is critically dependent on the properties of this compound

PRIMARY STANDARD

• High purity 

• Stability toward air

PRIMARY STANDARD

Absence of hydrate water

PRIMARY STANDARD

Ready availability at modest cost

PRIMARY STANDARD

Reasonably large molar mass

SECONDARY STANDARD

Standard solution / standard titrant

SECONDARY STANDARD

A reagent of known concentration that is used to carry out a titrimetric analysis

SECONDARY STANDARD

Expressed in terms of molarity and normality

SECONDARY STANDARD

• Be sufficiently stable 

• React rapidly with the analyte

SECONDARY STANDARD

React more or less completely with the analyte

DIRECT METHOD

A carefully weighed quantity of a primary standard is dissolved in a suitable solvent and diluted to an exactly known volume in a volumetric flask

Standardization

process of determining the exact concentration of a solution

STANDARDIZATION

A weighed quantity of a primary standard

STANDARDIZATION

A measured volume of another standard solution/secondary standard

DIRECT TITRATION METHOD

Titrant reacts directly with analyte

DIRECT TITRATION METHOD

A simple relationship exist between the titrant used and the analyte present

INDIRECT TITRATION METHOD

Replacement Titration Method

INDIRECT TITRATION METHOD

Employs a preliminary reaction in which the analyte is replaced by an equivalent amount of another substance which is then determined by titration

RESIDUAL TITRATION METHOD (BACK TITRATION METHOD)

A known excess of the titrant is added to the analyte solution

RESIDUAL TITRATION METHOD (BACK TITRATION METHOD)

Amount of analyte is found by difference

ACID-BASE

Many compounds, both inorganic and organic, are either acids or bases and can be titrated with a standard solution of a strong base or a strong acid

ACID-BASE

End points of these titrations are easy to detect, either by means of an (1) indicator or by (2) following the change in pH with a pH meter

PRECIPITATION

The titrant forms an insoluble product with the analyte

PRECIPITATION

• (1) Indicators can be used to detect the end point or the (2) potential of the solution can be monitored electrically

• Analyte + Titrant

COMPLEXOMETRIC

The titrant is a reagent that forms a water-soluble complex with the analyte, a metal ion

chelating agent ; EDTA

COMPLEXOMETRIC

The titrant is often a _

COMPLEXOMETRIC

Reverse titration may be carried out also

COMPLEXOMETRIC

Indicators can be used to form a highly colored complex with metal ion

REDOX

Involves the titration of an oxidizing agent with a reducing agent or vice-versa

difference

REDOX

There must be a sufficiently large _ between the oxidizing and reducing capabilities

REDOX

End points detected by (1) appropriate indicators or by (2) various electrometric means