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Gravimetric Analysis

Gravimetric Analysis. A History of Gravimetric Analysis

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Gravimetric Analysis

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  1. Gravimetric Analysis A History of Gravimetric Analysis Theodore W. Richards (1868 - 1928) …and his graduate students at Harvard developed or refined many of the techniques of gravimetric analysis of silver and chlorine. These techniques were used to determine the atomic weights of 25 of the elements by preparing pure samples of the chlorides of the elements, decomposing known weights of the compounds,and determining the chloride content by gravimetric methods. From this work Richards becamethe first American to receive theNobel Prize in Chemistry in 1914.

  2. Gravimetric analysis is the quantitative determination of analyte concentration through a process of precipitation of the analyte, isolation of the precipitate, and weighing the isolated product. Gravimetric methods are quantitative methods that are based on determining the mass of a pure compound to which the analyte is chemically related.

  3. Uses of gravimetric analysis… – Chemical analysis of ores and industrial materials – Elemental analysis of inorganic compounds

  4. Classifications of Gravimetric methods 1-Volatilization gravimetry, the analyte is separated from other constituents of a sample by conversion to a gas of known chemical composition. The weight of this gas then serves as a measure of the analyte concentration. 2-Precipitation gravimetry, the 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. 3-Electrogravimetry, the 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.

  5. Features or properties of Gravimetric Analysis 1- Traditional Method. 2- Cheap, easily available apparatus, simple to carry out. 3- Slow, especially when accurate results are required. 4- Wide range of sample concentrations (ng - kg). 5- No calibration required (except for the balance). 6- Accurate

  6. Volatilization Gravimetry The substance (analyte) to be determined is separated from the other constituents of a sample as a gas of known chemical composition, like H2O, CO2,….etc. A- Direct Method The volatile substance can be absorbed in a weighed quantity of a suitable medium (absorbent). B- Indirect Method The weight of the residue remaining after the volatilization of a sample is determined, and the amount of volatilized component is determined from the change in the weight.

  7. Applications of Volatilization Gravimetry 1: Determination of the percentage by mass of water in a hydrated salt. 2: determination of NaHCO3 in antacid tablets 3: Determining the inorganic ash content of an organic material, such as a polymer 4: determination of dissolved solids in natural waters and wastewaters.

  8. 1: Determination of the percentage by mass of water in a hydrated salt. • Hydrated Salt [ salt with water ] • Anhydrous Salt [ salt without water ] Some hydrated salts : CuSO4.5H2O, BaCl2.2H2O, MgSO4.7H2O The water molecules which are bound to the ions in the salt structure is called Water of Crystallization or Water of Hydration Percentage by mass of H2O

  9. 2: determination of NaHCO3 in antacid tablets 1- The analyte can be bicarbonate or a mixture of carbonate and bicarbonate. 2- placing the analyte in a solution containing an excess of H2SO4in a flask. 3-nitrogen gas gently bubbled through the solution as a carrier gas and does not take part in any reaction. 

  10. 4- Water vapor and carbon dioxide resulting from the reaction carried by nitrogen gas to the drying tubes. 5- the first tube contains CaSO4 to absorb the water vapor . 6- the second tube contains NaOH on asbestos to absorb the CO2.

  11. determination of NaHCO3 in antacid tablets

  12. 3: Determining the inorganic ash content of an organic material, such as a polymer This is an example of a direct volatilization gravimetric analysis. 1- Weighing the sample and placed in an appropriate crucible. 2- The organic material carefully removed by combustion, leaving behind the inorganic ash. 3- The crucible containing the residue is heated to a constant weight using either a burner or an oven before determining the mass of the inorganic ash.

  13. 4- Determination of dissolved solids in natural waters and wastewaters 1- In this method, a sample of water is transferred to a weighing dish and dried to a constant weight at either 103–105 oC or at 180 oC. 2- the residue is the weight of the TDS mass. TDS = total dissolved solids

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