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How are Cations Identified

Precipitate formed in hg 2 no 3 2 aq a red

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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 these reactions are Hg(OH) (s), Fe(OH) 3 (s), and Cd(OH) 2 (s). Week 2 – 6b Unknown Solution Reagent Added (20 drops ~ 1.0 mL) Reaction Significance HNO 3 White precipitate Hg present NaOH No precipitate Pb not present NH 3 Red/Brown precipitate Fe present NaOH White precipitate Cd present When 20 drops of HCl was added to the unknown solution, a white precipitate formed in the solution. What was formed should have been HgCl (s). When 20 drops of NaOH was added nothing had happened and there was no reaction meaning the Pb was missing. When 20 drops of 6M NH 3 was added to the unknown solution, a red/ brown precipitate was formed in the middle
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close to the bottom. An additional 20 drops of the reagent were added to form a solid brown precipitate at the bottom of the test tube which was Fe(OH) 3 (s). When 20 drops of 6M NaOH was added to the unknown solution, another white precipitate was formed which was Cd(OH) 2 (s). Equations 1) HCl (aq) + Hg (aq) HgCl (s) + H + (aq) 2) H 2 SO 4 (aq) + Ba 2+ (aq) BaSO 4 (s) + 2H + (aq) 3) NH 3 OH + Fe Fe(OH) 3 + 3NH 3 + (aq) 4) HNO 3 (aq) + Cd 2+ Cd(NO 3 ) 2 (aq) + H + (aq) 5) Cd(NO 3 ) 2 (aq) + H + (aq) + NaOH (aq) Cd(OH) 2 (s) + Na(NO 3 ) 2 (aq) + H + (aq) Flow Chart: Analysis of Cations Flow Chart Discussion The experiments main purpose was to identify cations in unknown solutions using the properties of the cations to figure it out. The individual analysis of each Nitrate salt and the cation it contained was extremely important when testing the unknown solution. Without the individual analysis, the flow chart could not have been compiled, and the unknown solution testing would have been unsuccessful. The flow chart was the reason behind the experiment to follow every step that we took to get to the next part and piece it all together. The selective precipitation and qualitative analysis were the processes behind the logic of the flow chart. The spot-plate was referenced during the formation of this chart. HCl was added first because it was shown to only react with the Hg I cation in Hg 2 (NO 3 ) 2 (aq) Nitrate salt. The order of the regents was very much important because if they were not done in order some may not have been taken out from the very beginning. As well as past cations, the next one needs to react with those that
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were left. With the removal of those two cations, the next step was determined to be NH 3 because it was observed to react with the Fe III and Cd II cations. The Fe III cations were able to be isolated and separated because the Cd II cations were dissociated back into the solution when excess reagent was added. Since NH 3 is a base, the solution was turned basic. The final reagent left to be added was NaOH . This woulc take care of the Cd II, and it would then be removed and the solution would be left without cations in it. The first cation to be separated from the known solution was Hg I. In the
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precipitate formed in Hg 2 NO 3 2 aq a red precipitate...

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