Sulfate Experiment

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Summary
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
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During this process, using an asheless filter paper is extremely important because if ordinary filter papers were used, some ash would remain with the barium sulfate precipitate. This would cause the final mass of the precipiate to appear higher than normal. The resulting percent sulfate would be falsely higher. To calculate the percent sulfate, the difference in the mass of empty crucible and the crucible containing the precipitate is calculated to find the mass of barium sulfate precipitate. The mass of barium sulfate is then converted to moles and multiplied by a 1:1 mole ratio followed by multiplying the molar mass of sulfate to determine the mass of sulfate in the unknown sample. Finally, the mass of sulfate is divided by the initial sample mass of 0.3500 and multiplied by 100 to determine the % sulfate in the original …show more content…
The supernatants were decant into the filter papers and the precipitate was rinsed and decant into the filter paper three times with warm DI water. The precipitate was then transferred into the filter paper with a stream of water of the wash bottle. After all of the precipitate was transferred, the material in the filter paper was washed three times with 5mL of hot DI water. A few drops of each washing were collected into a watch glass and tested with two drop of silver nitrate to determine whether there are still chloride ion contaminants. If the solution in the watch glass turn cloudy after silver nitrate is added, then the precipitate are still contaminated with chloride ion and need further washing with hot DI water. If the solution is clear and colorless, then no further washing is needed. The three precipitate sample was then folded within the filter paper and stored for 2 days inside the crucible until the next lab day. The following lab day, each crucible is heated on a Bunsen burner on a ring stand. The flame was moved around to avoid excessive initial heating and that the crucible is heated evenly. Once the filter paper was charred, the temperature of the flame was increased. When all of the black carbon residue has been removed, the temperature of the flame was maximized so that the tip of the blue flame cone is right below the wall of the crucible. The

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