112 CHM-153 Advance Study Assignment GENERAL UNKNOWN (pages 112-115) NAME DAT Re
ID: 556304 • Letter: 1
Question
112 CHM-153 Advance Study Assignment GENERAL UNKNOWN (pages 112-115) NAME DAT Refer to the procedures on pages 110 and 111 to answer the following questions... 1) The first thing you need to do with the general unknown is to precipitate the chlorides of Ag', Hg2 drops be enough to precipitate all the Group I cations? Explain. and Pb. We do this to a mixture of all the possible cations by adding 3 drops of 6M HCI solution. Will 3 2) If you did not get even a tiny bit of cloudiness with 3 drops of 6M HCI, what would you conclude? a) You do not have any silver or mercury, but might have lead. b) You do not have any Group I cations. c) You did not add enough 6M HCL. Explain your answer. 3) Give the steps in the procedure for the separation of the Group I cations from the Group I and lI cations.Explanation / Answer
Answer 1) The 6M HCl is more than enough to precipitate the cation of the group I. If you add more HCL or concentrated HCl on the contrary we risk to solubilize chloride. This is because we would allow formation of soluble chloride complex of our salt. As the concentration of Cl rise the soluble complex form. This complexes are soluble because they are charged molecule and therefore effectively solvated by water.
Answer 2) you do not have group I cation. As explain above 6M HCl is more then enough to precipitate group I cation.
Answer 3)
Group I cations
Add to the solution an excess of dilute HCl. If there is no change then other group is present. A white precipitate may contain Pb2+, Hg2 2+ or Ag+.
Filter and wash the precipitate and then add NH3 solution to the precipitate.
If the precipitate
does not change: Pb2+ present
turns black: Hg22+ present
dissolves: Ag+ present
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