Question

Write equations for the following separations. Indicate any conditions required for the reactions to occur, such as pH 5. a) Group III cations from Groupe IV cations b) Fe2+ and Cr3+ ions from Ni2+ ion. c) Fe2+ ion from Cr3+ ion. d) Ba2+ ion from Ca2+ ion. please help!!!

Answer 1

a) The separation of the Group III cations from the Group IV & V cations, the precipitate is treated with 6 M HCl which puts all the cations except for Ni2+ and Co2+ in solution. The precipitate of NiS and CoS is dissolved in aqua regia (12 M HCl and 6 M HNO3) and the two ions are identified by interactions with their specific reagent. The HCl solution of the other cations is made basic and treated with sodium hypochlorite which oxidizes Fe2+ to Fe3+. Following treatment with NH3, the precipitate contains Fe(OH)3 and Ni(OH)2 and the supernatant contains Al(OH)4 - and Zn(OH)4 2- . The precipitate is dissolved in H2SO4 and the presence of Fe3+ can be confirmed.

b)   Add excess concentrated NH4OH to Fe 2+ and Cr 3+ ions from Ni 2+ ion

& pour off the nickel from the ppts
Fe+2 & 2NH4OH --> Fe(OH)2 (s) & 2NH4+
Cr+3 & 3NH4OH --> Cr(OH)3 (s) & 3NH4+

Ni+3 & 6 NH3 --> [Ni (NH3)6]+3 (aq)

c) Add NaOH to Fe 2+ ion from Cr 3+ ion, pour off the solution of chromium from the Iron ppt

2 NaOH & Fe+2 --> Fe(OH)2 (s) & 2 Na+

4 NaOH & Cr+3 --> [Cr (OH)4]-1 (aq) & 4 Na+

d) In principle, the ions Ba2+ and Ca2+ can be separated by the difference in solubility of their fluorides, BaF2 and CaF2. If you have a solution that is 0.10 M in both Ba2+ and Ca2+, CaF2 begins to precipitate first as fluoride ion is added slowly to the solution.