Gravimetric Analysis
Gravimetric Analysis
CHEM 200-03
Fall Semester 2012
September 19, 2012
Jeff Marasigan
Abstract Gravimetric analysis is based on the quantitative isolation of the desired constituent the analyte of interest from the sample in highly pure form or in some combined form and weighing the isolated constituent. The desired constituent is usually isolated or separated by precipitation. From the weights of sample and precipitate, the percentage of the constituent in the original sample can be calculated. Precipitation is effected by inorganic or organic precipitating agents. Two common inorganic precipitating agents are silver nitrate, which is used to precipitate halide ions such as chloride, and barium chloride, which is used to precipitate sulfate ion. In all of these precipitation reactions, the product is a salt because it is formed by reactions between cations and anions.Thus the bonding is ionic or electrovalent. The three major requirements for a good gravimetric analysis are that (a) the reagent will react only with the analyte of interest to form a precipitate, (b) it forms one and only one product with the analyte and (c) that the analyte precipitates quantitatively from solution, that is, >99.99% In aqueous solution silver ion undergoes the following reaction with chloride:
Ag+(aq) + Cl-(aq) ?? AgCl(s)
Silver chloride is a relatively insoluble compound with a solubility product
Ksp =[Ag+][Cl-] = 1.8 x 10-10.
Introduction
Gravimetric analysis, which by definition is based upon the measurement of mass, can be generalized into two types; precipitation and volatilization. The quantitative determination of a substance by the precipitation method of gravimetric analysis involves isolation of an ion in solution by a precipitation reaction, filtering, washing the precipitate free of contaminants, conversion of the precipitate to a product of known composition, and finally weighing the precipitate and determining its mass by difference.
CHEM 200-03
Fall Semester 2012
September 19, 2012
Jeff Marasigan
Abstract Gravimetric analysis is based on the quantitative isolation of the desired constituent the analyte of interest from the sample in highly pure form or in some combined form and weighing the isolated constituent. The desired constituent is usually isolated or separated by precipitation. From the weights of sample and precipitate, the percentage of the constituent in the original sample can be calculated. Precipitation is effected by inorganic or organic precipitating agents. Two common inorganic precipitating agents are silver nitrate, which is used to precipitate halide ions such as chloride, and barium chloride, which is used to precipitate sulfate ion. In all of these precipitation reactions, the product is a salt because it is formed by reactions between cations and anions.Thus the bonding is ionic or electrovalent. The three major requirements for a good gravimetric analysis are that (a) the reagent will react only with the analyte of interest to form a precipitate, (b) it forms one and only one product with the analyte and (c) that the analyte precipitates quantitatively from solution, that is, >99.99% In aqueous solution silver ion undergoes the following reaction with chloride:
Ag+(aq) + Cl-(aq) ?? AgCl(s)
Silver chloride is a relatively insoluble compound with a solubility product
Ksp =[Ag+][Cl-] = 1.8 x 10-10.
Introduction
Gravimetric analysis, which by definition is based upon the measurement of mass, can be generalized into two types; precipitation and volatilization. The quantitative determination of a substance by the precipitation method of gravimetric analysis involves isolation of an ion in solution by a precipitation reaction, filtering, washing the precipitate free of contaminants, conversion of the precipitate to a product of known composition, and finally weighing the precipitate and determining its mass by difference.