Gravimetry is a quantitative analytical technique in chemistry for determining the concentration or quantity of a specific substance in a sample by measuring either the mass of a precipitate or the change in mass of a sample before and after a chemical reaction. This method is based on the principle that the mass of a substance is directly proportional to its quantity, making it a highly accurate and reliable method for chemical analysis.
In gravimetric analysis, a known amount of the sample undergoes a chemical reaction that results in the formation of a solid precipitate. Separate this precipitate from the solution, typically by filtration, and precisely measure its mass using a sensitive balance. To calculate the concentration or quantity of the substance of interest in the original sample, you measure the mass of the precipitate and apply stoichiometry to the chemical reaction.
Gravimetry finds extensive use in various applications, including the analysis of metal ions, organic compounds, and minerals. It is especially valuable when demanding high precision and accuracy and when other analytical techniques may not offer the same level of reliability or sensitivity.
Gravimetric analysis is a quantitative analytical method that determines the concentration or quantity of a specific substance in a sample by measuring the mass of a precipitate formed during a chemical reaction. It relies on the fundamental principle that the mass of a substance is directly proportional to its quantity. Here is a detailed overview of the principles and steps involved in gravimetric analysis:
Principles of Gravimetric Analysis:
Gravimetric analysis relies on the fundamental principle of the law of conservation of mass, which states that matter cannot be created or destroyed in a chemical reaction. When a specific chemical reaction occurs in a solution, it produces a solid precipitate. We then isolate and dry the precipitate and accurately measure its mass. By knowing the reaction’s stoichiometry, one can calculate the quantity or concentration of the analyte in the original sample.
Steps Involved in Gravimetric Analysis:
1. Sample preparation:
The first step in gravimetric analysis is to prepare a representative material sample. The sample should be homogeneous and free of impurities that could interfere with the analysis.
2. Dissolution:
Dissolve the sample in an appropriate solvent or a solvent mixture to create a solution. Typically, we conduct this dissolution process in a beaker or flask.
3. Precipitation:
Add a carefully selected reagent (precipitating agent) to the solution, resulting in the formation of a solid precipitate. The selection of the reagent depends on the analyte to be determined and its compatibility with the precipitating agent.
4. Digestion:
Once the precipitate has formed, heat the mixture or let it stand for a specific period to ensure complete and uniform precipitation. This step is referred to as “digestion.”
5. Filtration:
Separate the solid precipitate from the liquid (filtrate) by employing filtration techniques, which may involve vacuum or gravity. The precipitate is retained on a filter paper, and the filtrate is collected separately.
6. Washing:
Wash the precipitate with an appropriate solvent, usually distilled water, to eliminate any remaining soluble impurities or unwanted ions. Collect the washings separately, often combining them with the original filtrate.
7. Drying:
Place the filter paper with the precipitate in an oven and dry it to eliminate any remaining moisture. Weigh the filter paper and precipitate both before and after drying.
8. Weighing:
Precise weighing of the filter paper and dried precipitate is performed using an analytical balance. The difference in mass before and after drying represents the mass of the precipitate.
9. Calculation
Calculate the quantity or concentration of the analyte in the original sample by taking into account the stoichiometry of the reaction and utilizing the mass of the precipitate. This calculation often involves molar ratios and the molar mass of the precipitate.
10. Reporting Results:
Report the analysis results, including the concentration or quantity of the analyte in the sample, in the desired units.
