Analytical ChemistryHard
Question
A solution containing SCN- ions can be used to test one or more out of : Fe3+, Co2+ , Cu2+, Ag+ and Hg2+.
Options
A.Fe3+ and Co2+ only
B.Co2+, Cu2+, Ag+ and Hg2+
C.Fe3+ , Cu2+, Co2+ and Hg2+
D.All
Solution
CoCl2 + 4NH4SCN 
(NH4)2 [Co(SCN)4] (blue colour in ethereal layer) + 2NH4Cl.
Cu2+ + 3SCN- → CuSCN↓ (white) + (SCN)2.
FeCl3 + 3NH4SCN
Fe(SCN)3 (blood red colour) + 3NH4Cl.
Ag+ + SCN- → AgSCN ↓ (white).
Co2+ + 4SCN- + Hg2+ → Co[Hg(SCN)4] ↓ (deep blue).
(NH4)2 [Co(SCN)4] (blue colour in ethereal layer) + 2NH4Cl.Cu2+ + 3SCN- → CuSCN↓ (white) + (SCN)2.
FeCl3 + 3NH4SCN
Fe(SCN)3 (blood red colour) + 3NH4Cl.Ag+ + SCN- → AgSCN ↓ (white).
Co2+ + 4SCN- + Hg2+ → Co[Hg(SCN)4] ↓ (deep blue).
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