Week 11-14 Classical and Instrumental Methods of Analysis

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Cards (43)

Gravimetry 
Techniques in which we measure mass or a change in mass
Gravimetric methods 
Quantitative methods that are based on determining the mass of a pure compound to which the analyte is chemically related
Precipitation gravimetry 
Analyte is separated from a solution of the sample as a precipitate and is converted to a compound of known composition that can be weighed
Volatilization gravimetry 
Analyte is separated from other constituents of a sample by converting it to a gas of known chemical composition. The mass of the gas then serves as a measure of the analyte concentration
Electrogravimetry 
Analyte is separated by deposition on an electrode by an electrical current. The mass of this product then provides a measure of the analyte concentration
Properties of precipitates and precipitating reagents 
Reagent should react specifically or at least selectively with the analyte
Precipitate should be easily filtered and washed free of contaminants
Precipitate should have sufficiently low solubility that no significant loss of the analyte occurs during filtration and washing
Precipitate should be unreactive with constituents of the atmosphere
Precipitate should be of known chemical composition after it is dried or, if necessary, ignited
Methods for homogeneous generation of precipitating agents
1. Urea
2. Trimethyl phosphate
3. Ethyl oxalate
4. Dimethyl sulfate
5. Trichloroacetic acid
6. Thioacetamide
7. Biacetylhydroxylamine
8. 8-Acetoxyquinoline
Titrimetry 
Any method in which volume is the signal
Titrant 
The reagent added to a solution containing the analyte and whose volume is the signal
Equivalence point 
The point in a titration where stoichiometrically equivalent amounts of analyte and titrant react
End point 
The point in a titration where we stop adding titrant
Indicator 
A colored compound whose change in color signals the end point of titration
Titration error 
The determinate error in a titration due to the difference between the end point and the equivalence point
Standard solutions 
Should be sufficiently stable so that it is necessary to determine its concentration only once
Should react rapidly with the analyte so that the time required between additions of reagent is minimized
Should react more or less completely with the analyte so that satisfactory end points are realized
Should undergo a selective reaction with the analyte that can be described by a balanced equation
Primary standard 
A highly purified compound that serves as a reference material in titrations and in other analytical methods
Requirements for a primary standard
High purity
Atmospheric stability
Absence of hydrate water so that the composition of the solid does not change with variations in humidity
Modest cost
Reasonable solubility in the titration medium
Reasonably large molar mass so that the relative error associated with weighing the standard is minimized
Neutralization titrations 
Widely used to determine the amounts of acids and bases, and to monitor the progress of reactions that produce or consume hydrogen ions
Common standard reagents used in acid/base titrations
HCl
HClO4
H2SO4
NaOH
KOH
Important acid-base indicators 
Thymol blue
Methyl yellow
Methyl orange
Bromocresol green
Methyl red
Bromocresol purple
Bromothymol blue
Phenol red
Cresol purple
Phenolphthalein
Thymolphthalein
Alizarin yellow GG
VOLUMETRIC METHOD OF ANALYSIS: Titrations are widely used in analytical chemistry to determine acids, bases, oxidants, reductants, metal ions, proteins, and many species.
Gravimetric Method is the mass of the analyte or some compounds chemically related to is being determined. Ex: Precipitation Gravimetry Volatilization Gravimetry
Volumetric (Titrimetric) Method: the amount of analyte is determined by measuring the volume of a solution of known concentration. Ex: Acid-Base Titration, Precipitation Titration, Complexometric Titration
Gravimetric methods 
Quantitative methods that are based on determining the mass of a pure compound to which the analyte is chemically related
Precipitation gravimetry 
1. Analyte is separated from a solution of the sample as a precipitate
2. Precipitate is converted to a compound of known composition that can be weighed
Volatilization gravimetry 
1. Analyte is separated from other constituents of a sample by converting it to a gas of known chemical composition
2. Mass of the gas then serves as a measure of the analyte concentration
Electrogravimetry 
1. Analyte is separated by deposition on an electrode by an electrical current
2. Mass of this product then provides a measure of the analyte concentration
Precipitation gravimetry 
The analyte is converted to a sparingly soluble precipitate
Precipitation gravimetry  
where analyte is converted to a sparingly soluble precipitate, is filtered, washed free of impurities, converted to product of known composition by heat treatment, and weighed
Neutralization titrations are widely used to determine the amounts of acids and bases.
Titrations are based on a reaction between analyte and a standard reagent known as the titrant.
1. acid base titrations, in which an acidic or basic titrant reacts with an analyte that is a base or an acid
2. complexometric titration involving a metal-ligand complexation reaction
4. redox titrations - where titrant is an oxidizing or reducing agent
3.) precipitation titrations, in which the analyte and titrant react to form a precipitate
The two most common gravimetric methods based on volatilization are those for determining what?
water , carbon dioxide
Titrimetry 
Any method in which volume is the signal
Titrant 
The reagent added to a solution containing the analyte and whose volume is the signal
Equivalence point 
The point in a titration where stoichiometrically equivalent amounts of analyte and titrant react
End point 
The point in a titration where we stop adding titrant
Indicator 
A colored compound whose change in color signals the end point of titration