Date Name oulution is known to contain either Cu ion, Bi\" ion, or both ions. De
ID: 556540 • Letter: D
Question
Date Name oulution is known to contain either Cu ion, Bi" ion, or both ions. Describe a single test that would identify the ionls) Group II Cations Unknown: Post-lab Questions the ioo(s) present. State what would be observed if (a) both ions were presemt ion was present. (b) if only Cu ion was ion was present, (c) if only Bi tain either CP. ion or [SnCI ion. Give a two-step procedure that ch ion is present. What would you expect in each step? 2. A solution is known to con would allow the determination of whi s ther Bi" ion or Cd ion. Describe a single test that would Explain what you would expect in each case. determine which ion is present. The experimental procedure presented in this experiment was used to analyze a solution containing Bi', Cu, Cd, and Sn'" ions. For each of the following changes in the procedure, predict the effect on the separation of the involved cations: 4. (b) The Group II precipitation was carried out at pH 5.0 instead of pH 0.5Explanation / Answer
1) Add 15 drops of 6M NH3•H2O to test tube containing Cu2+ and Bi3+ stir and centrifuge for two minutes.
Ammonia solution is somewhat basic, both Cu2+ and Bi3+ will precipitate as insoluble hydroxides
Cu2+ + 2 NH3 + 2 H2O --> Cu(OH)2(s) + 2 NH4+
Bi3+ + 3 NH3 + 3 H2O --> Bi(OH)3(s) + 3 NH4+
As more NH3 solution is added, the insoluble Cu(OH)2 will dissolve forming the dark blue [Cu(NH3)4]2+ complex ion, but the solid Bi(OH)3 will remain.
Cu2+ + 4 NH3 (aq) ----> [Cu(NH3)4]2+(aq)
Filtration will give copper in the filtrate as the tetra amine copper (II) ion while retaining bismuth on filter paper. Wash the precipitate and add 10 drops of 0.1M SnCl2 and 10 drops of 3M NaOH to it and stir. If a black precipitate is formed, it confirms the presence of Bi3+.
2Bi(OH)3 (s) + 3[Sn(OH)4]–(aq) 2Bi(s) + 3[Sn(OH)6]2–(aq)
To one-half of the filtrate, add 10 drops of 6 MNH3·H2O. A dark blue solution confirms the presence of Cu2+.
To the other half of the filtrate, add 4 drops of 0.1 M K4[Fe(CN)6]. A reddish-purple precipitate confirms the presence of Cu2+.
2Cu2+(aq) + K4[Fe(CN)6](aq) Cu2[Fe(CN)6](s) + 4K+
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