An unknown solution may contain some of the cations listed below. One student preformed a series of experiments to determine what ions are in the solution. Based upon the experiments performed by the students, the results are as follows:
a) On addition of 6 M HCl, a white precipitate was observed. The white precipitate was then mixed with NH3 where it dissolved. The contents were then centrifuged and the supernatant was removed (S1).
b) On the addition of 1 ml (20 drops) of 1 M thioacetamide (CH3CSNH2) to (S1) the test tube was then heated in a boiling water bath for 5 mins. After the 5 mins, it was removed from the heat and left to cool. After the contents were cooled, they were then centrifuged and the supernatant removed (S2) and the precipitate (P1) was kept for further testing. The P1 was then rinsed in distilled water. 2ml of distilled water was then added to P1 followed by 15 drops of 6M potassium hydroxide (KOH). 1 drop of 1 M thioacetamide (CH3CSNH2) was then added to the precipitate and then heated in a water bath for 3 mins. The contents were then centrifuged and the supernatant (S3) was then removed. Distilled water was then added to P1 followed by 0.75 ml of 6 M NH3. The P1 dissolved giving a deep blue color.
c) 6 M HCl to S3 to acidify to solution. No reaction was observed.
d) 0.75 ml (15 drops) of 5M ammonium chloride (NH4Cl) and 6M NH3 were added to S2 until the solution turned basic, a precipitate (P2) was then observed. 1 ml (20 drops) of 1 M thioacetamide (CH3CSNH2), was then added to (P2), mixed thoroughly, then heated in a water bath for 5 mins. The solution was then cooled, centrifuged and the supernatant (S4) removed. The precipitate was then washed three times with distilled water. 3ml (60 drops) of sulfate/hydrogen sulfate (SO42-/HSO4-) buffer was then added and all of the precipitate dissolved. 1.0 ml (20 drops) of 6M NaOH was then added to the solution and a reddish-brown precipitate was observed. The contents were then centrifuged and the supernatant (S5) was removed. 2 ml (40 drops) of distilled water was then added to the reddish-brown precipitate, followed by 1 ml (20 drops) of 6 M HCl, then 3 drops of 1M potassium thiocyanate (KSCN) and a dark red solution was then observed.
e) 6M of HCl was then added to S5, followed by 3M NH3. The solution was then warmed in a water bath. No precipitate was observed.
Classify the following ions as present, absent, or undetermined from the observations made above. (input the whole word)
Silver:
Aluminium:
Barium:
Calcium Blank:
Zinc:
Iron (Fe3+):
Copper:
Antimony (Sb3+):
Nickel (Ni2+):
To determine the presence, absence, or undetermined status of each ion based on the given observations, let's go through each ion separately:
Silver (Ag+):
- In step a), when 6 M HCl was added, a white precipitate was observed. This suggests the presence of a chloride-containing compound.
- In step b), the precipitate obtained from step a) dissolved when NH3 was added. This confirms the presence of Ag+ ions because silver chloride (AgCl) dissolves in excess ammonia.
- In step c), when 6 M HCl was added to S3, no reaction occurred, indicating that Ag+ ions are not present in S3.
Conclusion: Silver (Ag+) is present.
Aluminium (Al3+):
- There is no specific evidence for the presence or absence of aluminium based on the given observations.
Conclusion: Aluminium (Al3+) is undetermined.
Barium (Ba2+):
- There is no specific evidence for the presence or absence of barium based on the given observations.
Conclusion: Barium (Ba2+) is undetermined.
Calcium (Ca2+):
- There is no specific evidence for the presence or absence of calcium based on the given observations.
Conclusion: Calcium (Ca2+) is undetermined.
Zinc (Zn2+):
- There is no specific evidence for the presence or absence of zinc based on the given observations.
Conclusion: Zinc (Zn2+) is undetermined.
Iron (Fe3+):
- There is no specific evidence for the presence or absence of iron based on the given observations.
Conclusion: Iron (Fe3+) is undetermined.
Copper (Cu2+):
- There is no specific evidence for the presence or absence of copper based on the given observations.
Conclusion: Copper (Cu2+) is undetermined.
Antimony (Sb3+):
- There is no specific evidence for the presence or absence of antimony based on the given observations.
Conclusion: Antimony (Sb3+) is undetermined.
Nickel (Ni2+):
- There is no specific evidence for the presence or absence of nickel based on the given observations.
Conclusion: Nickel (Ni2+) is undetermined.
In summary, the classification of the ions is as follows:
Silver: Present
Aluminium: Undetermined
Barium: Undetermined
Calcium: Undetermined
Zinc: Undetermined
Iron (Fe3+): Undetermined
Copper: Undetermined
Antimony (Sb3+): Undetermined
Nickel (Ni2+): Undetermined