Determining Weight % Of Sulfate Inside An Unknown Sample Essay

1840 Words Sep 25th, 2015 8 Pages
The goal of the experiment was to determine weight % of sulfate inside an unknown sample compose of Na2SO4. The sample was dried, weighed and dissolved in water and hydrochloric acid. Barium chloride was then added in excess to drive the precipitation process to completion. Heat was use to digest the precipitate before it was filtered through an ashless filter paper and ignited to constant weight. From mass of the sample and mass of the precipitate, the percentage of sulfate in the unknown sample was calculated.

Background and Theory
In gravimetric precipitation analysis, an insoluble compound is formed when a precipitating reagent is added to react with the analyte. The resulting precipitant with a known composition can then be filtered and weighed to determine information about the analyte. In this experiment, an unknown sample containing Na2SO4 was dissolved and BaCl was added as a precipitating agent. The overall reaction is Ba2+ + SO42- → BaSO4. Barium Chloride was chosen as the precipitating agent because the resulting product BaSO4 has a very low Ksp. According to the Handbook of Chemistry and Physics, the solubility of barium sulfate at 25° C and 100° C is 0.000246 and 0.000413 g/100mL solution respectively. This mean that the resulting precipitant is extremely insoluble even at 100 degree. The amount of precipitate that remain dissolved would not make a significant difference in the result. In addition, excess amount of barium chloride was used…

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