5. A 0.5664 g ore sample is dissolved in nitric acid and then filtered. The aluminum is present in solution as Al3+. The solution is made basic with ammonium hydroxide, NH4OH, and the aluminum hydroxide, Al(OH)3 (FW 78.004), precipitates. This gel is filtered in a porous glass crucible, rinsed with dilute ammonium hydroxide, ignited, cooled in a desiccator, and weighed. The resulting alumina, Al2O3 (FW 101.94), weighed 0.1605 g. Why is the solution filtered after acid dissolution? To remove insoluble matrix material (like sand, etc.) 6. In #5, why rinse with ammonium hydroxide solution? To avoid peptization or loss of precipitate. Ammonium hydroxide is a volatile electrolyte. 7. In #5, what chemical transformation takes place during ignition? (Show the balanced chemical equation) 2Al(OH)3 -> Al2O3 + 3H2O 8. In #5, why use a desiccator during cooling? To avoid weight gain by adsorption of atmospheric water. 9. In #5, calculate the weight percent Al (AW 26.9815) in the sample.
5. A 0.5664 g ore sample is dissolved in nitric acid and then filtered. The aluminum is present in solution as Al3+. The solution is made basic with ammonium hydroxide, NH4OH, and the aluminum hydroxide, Al(OH)3 (FW 78.004), precipitates. This gel is filtered in a porous glass crucible, rinsed with dilute ammonium hydroxide, ignited, cooled in a desiccator, and weighed. The resulting alumina, Al2O3 (FW 101.94), weighed 0.1605 g. Why is the solution filtered after acid dissolution? To remove insoluble matrix material (like sand, etc.)
6. In #5, why rinse with ammonium hydroxide solution? To avoid peptization or loss of precipitate. Ammonium hydroxide is a volatile electrolyte.
7. In #5, what chemical transformation takes place during ignition? (Show the balanced chemical equation) 2Al(OH)3 -> Al2O3 + 3H2O
8. In #5, why use a desiccator during cooling? To avoid weight gain by adsorption of atmospheric water.
9. In #5, calculate the weight percent Al (AW 26.9815) in the sample.
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