Gravimetric Analysis and Precipitation Equilibria


1. Precipitation gravimetry (oldest)

2. Electrogravimetry

3. Volatilization gravimetry and Thermogravimetry

4. Gravimetric titrimetry

5. Particulate gravimetry

When signal is mass of a precipitate, the method is called precipitation gravimetry. For example, determination of Cl– by precipitating it as AgCl.

Electrogravimetry: the analyte is deposited on one electrode in an electrochemical cell. For example

• oxidation of Pb2+, and its deposition as PbO2 on a Pt anode or

• reduction of Cu2+ to Cu and its electrodeposition on a Pt cathode, for direct analysis for Cu2+.

Volatilization gravimetry: when thermal or chemical energy is used to remove a volatile species. For example, determining moisture content using thermal energy to vaporize H2O. Also carbon and hydrogen in an organic compound may be determined by combustion with O2 to CO2 and H2O.

Gravimetric titrimetry, mass of titrant intead of its volume is measured. (Mass measurements are much more accurate and precise)

Finally, in particulate gravimetry the analyte is determined following its re-moval from the sample matrix by filtration or extraction. The determination of sus-pended solids is oneexample of particulate gravimetry.

Precipitation Gravimetric Analysis

• Gravimetric Analysis – one of the most accurate and precise methods of macro-quantitative analysis.

• Analyte is selectively converted to an insoluble form and precipitated quantitatively from its solution.

• Precipitate is treated to make it easily filterable and then filtered, dried and finally its mass is measured.

• Analyte mass is then calculated on the basis of the chemical composition of ppt and its mass.

Why use gravimetric analysis?

– Conducted with simple apparatus.

– Interpretation of results is easy – readings are directly related to analyte amount.

– Provides very accurate and precise results – in fact gravimetric results are used to check the accuracy of other methods.

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