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How are Cations Identified

With a flow chart made every step could be followed

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determined the unknown can then be easily determined. With a flow chart made every step could be followed to discover the unknown cation. 20 drops (approximately 1.0 mL) of the first reagent was added to the unknown solution. When a precipitate formed it was a given that a cation from the flow chart was present in the unknown solution. When a precipitate formed, the solution was centrifuged to separate all the precipitate from the solution. The unknown solution was then decanted into a separate 20.0 mL test tube and another 1.0 mL of the next reagent was added to the unknown solution. This was repeated with the remaining reagents that formed precipitate. Using the flow chart it was clear which cation separated or stayed with the excess regent, and with this information it was possible to figure out if the unknown substance contained the specific cation. One reason the regent was added, was because if it had not been it could have possibly been overlooked. For this cation,
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another 1.0 mL was added to the unknown solution. After this step, the last reagent was added and followed the standard steps for reagents. Once all the data from the unknown solution was compiled in a chart, it could be determined which cations were present in the unknown aqueous solution. Results Week 1 Figure #1: Original Physical State for the Metal Cations Hg 2 (NO 3 ) 2 Clear Fe(NO 3 ) 3 Very light yellow Cd(NO 3 ) 2 Dark yellow Pb(NO 3 ) 2 Clear Figure #2 Metal Cation (20 drops ~ 1.0 mL) Reagent Added (10 drops ~0.5 mL) Hg 2 (NO 3 ) 2 Pb(NO 3 ) 3 Fe(NO 3 ) 2 Cd(NO 3 ) 2 HCl – 6M White precipitate milky No change Color change yellow No change H 2 SO 4 – 3M White precip. milky White/ milky clear No change NH 3 – 6M Black color residue Milky White ppt Red/brown ppt No change HNO 3 – 6M Clear, no change clear no change Yellow No change NaOH – 6M Black color residue No change Red/brown ppt Cloudy milky
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When 10 drops of the HCl was added a cloudy, white precipitate formed in the Hg 2 (NO 3 ) 2 and changed the Fe color from a light yellow color, to a bright yellow. The precipitate that formed in this step was HgCl (S) . following the HCl, When NH 3 was added, a red precipitate was formed in Fe(NO 3 ) 3 (aq) There was also a precipitate also formed in excess of the reagent in the Cd(NO 3 ) 2 (aq). The two precipitates formed from these reactions are Fe(OH) 3 (s) and Cd(OH) 2 (s). Hg 2 (NO 3 ) 2 (aq) solution where the color changed from clear, to black that left a little residue or powder substance. When 10 drops of the H 2 SO 4 was added a white precipitate formed with the Hg 2 (NO 3 ) 2 with a foggy/ cloudy shape too it. The sulfuric acid also changed the Fe(NO 3 ) 3 from a yellowish, to a clear color. When 20 drops of HNO 3 (aq) was added to the cation solutions, Fe(NO 3 ) 3 (aq) went from a yellow solution to a clear color. Nothing else had change, so NaOH (aq) had to be added. When 20 drops of NaOH (aq) was added to the cation solutions, a black precipitate formed in Hg 2 (NO 3 ) 2 (aq), a red precipitate formed in Fe(NO 3 ) 3 (aq), and a cloudy/ white precipitate formed in excess when added to Cd(NO 3 ) 2 (aq). The precipitates that formed in
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