Determination of Cations and Anions through Elimination and Confirmation Tests By: Symantha Resendiz
A topic of great importance to all scientists is the identification of compounds, which is relevant in all aspects of their work in some way shape or form. Weather it may be determining what is causing sickness or what is polluting the air, it is very prevalent in the science world. In project 2, identification of cations and anions was preformed through a series of confirmation and elimination tests that ultimately led to identifying an unknown ionic compound made of cations and anions. Materials and Methods
Part 1- Cation Tests
To begin, 5 centrifuge tubes were added 10 drops of one cation and labeled correspondingly, and the initial color of each solution was recorded. To being the metal hydroxide test, each tube was then added 6 M NaOH drop wise (about 20 drops) until a precipitate was seen. To each solution that formed a precipitate, 10 more drops of 6 M NaOH were added. This was to test to see if any solution was amphoteric, where any insoluble metal precipitate dissolved after the additional 6 M NaOH was added. The results were recorded and each solution was disposed of. To being the ammonia test, 5 new centrifuge tubes were each added 10 drops of one cation and labeled correspondingly. 15 M NH4OH was then added drop wise (about 20 drops) to each solution and the color of the solution and/or the color of the precipitate formed was recorded. 10 more drops of 15 M NH4OH was added to each solution and any changes were recorded, and the solutions were disposed of. To begin the flame confirmation tests, 20 drops of each cation were added to its labeled centrifuge tube. A Bunsen burner was then connected to the gas jet and lit to where a sharp blue cone was visible in the flame. A Nichrome loop was then soaked in HCl and placed in the flame until there was no color change in the flame. This insured there was no further solution on the loop. The loop was then placed in each metal solution and the color of the flame was recorded. This process was repeated for each of the solutions, using cobalt glass to view the color of the flame, and was then recorded. Part 2- Anion Tests
To begin, 4 centrifuge tubes were added 10 drops of one anion and labeled correspondingly, and the initial color of each solution was recorded. 0.1 M AgNO3 was added to each tube, drop wise, to begin the silver nitrate elimination test. The color of each precipitate was recorded, then additional 0.1 M AgNO3 was added until no further precipitate was formed and the results were recorded. Each solution that produced a precipitate was then centrifuged for 30 seconds, then the liquid layer was discarded and 5 drops of distilled water were added to the leftover precipitant. HNO3 was then added to each solution, mixing in between each drop, until it turned acidic by testing it with litmus paper. Solutions that their precipitate did not dissolve with HNO3 were then centrifuged for 30 seconds, the liquid layer was discarded and 5 drops of distilled water were added to the leftover precipitant. 6 M HNO3 was then added, mixing in between each drop, until the solution turned acid and all results were recorded. For the Chloride anion confirmation test, 10 drops of chloride was added to a clean centrifuge tube. 6 M HNO3 was added by drops, until blue litmus paper confirmed the solution turned acidic by turning red. 10 drops of 0.1 M AgNO3 was added, the solution was centrifuged for 30 seconds, and the liquid layer was discarded. 4 drops of 6 M NH4OH was added to the precipitant to dissolve it. 6 M HNO3 was then added until the precipitant reformed to confirm that the sample contained chloride. For the sulfate confirmation test, 10 drops of sulfate was added to a clean centrifuge tube. 6 M HNO3 was then drop wise until the litmus paper confirmed the solution was acidic. 0.1 M BaCL2 was added by drops until precipitate was observed and the results...
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