GRAVIMETRIC ANALYSIS
Introduction to Gravimetric Analysis:
Gravimetric analysis is a quantitative method in which a substance is converted into an insoluble precipitate, separated, dried, and weighed to determine its amount in the original sample.
Since it is based on mass measurement, it is one of the most accurate analytical techniques used in laboratories.
Principles of Gravimetric Analysis:
Law of Mass Action:
The rate of reaction depends on concentration of reactants. Adjusting concentrations helps drive the reaction toward complete precipitation.
Solubility Product (Ksp):
Precipitation occurs when ionic product exceeds the solubility product constant (Ksp).
Common Ion Effect:
Addition of a common ion reduces solubility and increases precipitation efficiency.
Types of Gravimetric Analysis:
- Physical Gravimetry: Separation based on physical properties
- Thermogravimetry: Measures weight change on heating
- Electrodeposition: Metal deposited on electrode and weighed
- Precipitative Gravimetry: Formation and weighing of precipitate
Steps in Gravimetric Analysis:
- Sampling: Representative sample selection
- Precipitation: Formation of insoluble compound
- Digestion: Improves crystal size and purity
- Aging: Stabilizes precipitate
- Filtration: Separation of solid and liquid
- Washing: Removes impurities
- Drying/Ignition: Removes moisture and stabilizes form
- Weighing: Accurate mass measurement
- Calculation: Use gravimetric factor to determine analyte
Co-precipitation:
Contamination of precipitate due to adsorption or trapping of impurities during crystal formation.
Applications of Gravimetric Analysis:
- Chloride Estimation: As silver chloride (AgCl)
- Lead Estimation: As lead chromate
- Nickel Estimation: As nickel–dimethylglyoxime complex
