THE GRAVIMETRIC DETERMINATION
To determine the amount of Sulfate in an Unknown sulphate sample. 2. To perform and develop skills in precipitation Gravimetric method of quantitative analysis.
Gravimetric analysis is one of the oldest analytical techniques and for this reason is referred to as a "classical method." Gravimetric procedures are usually very accurate, but more tedious than other methods. The only major equipment needed for gravimetric analysis is an accurate balance.
Sulfur can be determined gravimetrically. Sulfur is found in minerals such as iron pyrite, gypsum and coal. Coal may contain as much as 4% sulfur in various forms: pyritic sulfur (as S 2 2-), sulfur in sulfates (as SO42-) and in a variety of organic forms, such as thiophenols and thiophenes. When coal with high sulfur content is burned sulfur dioxide is formed which is a major primary air pollutant. Obviously the value of coal as a fuel decreases as the sulfur content increases. For this reason, the analysis of coal for sulfur is extremely important. The American Society for Testing and Materials (ASTM) has developed a standard analysis method for sulfur as sulfate in coal, which is the basis for this experiment.
In any precipitation gravimetric analysis, the species to be determined is reacted with a reagent to yield a product that is: a) of known composition, b) is relatively pure, and c) of low solubility. Knowing the mass of the dried product and the mass of the original sample and their formula weights (to create a gravimetric factor), the percent of the species to be determined can be calculated.
In the analysis for sulfate, the sample to be analyzed is brought into solution and reacted with a solution of BaCl2, a source of Ba2+, to yield BaSO4 as a white precipitate. In the procedure, the solution is first acidified with HCl(aq) to: a) prevent the precipitation of BaCO3 and Ba(OH)2, and b) aid the formation...
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