Your idiot lab mate has done it again-didn\'t label the beakers of ligands that
ID: 975964 • Letter: Y
Question
Your idiot lab mate has done it again-didn't label the beakers of ligands that you so carefully measured out for a lab involving cobalt complexes. You mixed each of these ligands with a dilute solution of Co(ll), and heated for a while with H2O2 to produce the Co(lll)U compounds. They are vividly colored! While excited by the chromatic feast before your eyes, now you have to sleuth out which beaker contained which ligand, and justify your choices with a brief explanation. Your explanation should detail the sigma/pi donor/acceptor properties of each ligand, and how those relate to the colors of the complex. Ligand solutions: NH_3, KCN, C_sF, H_2O Colors of solutions formed: colorless, green, orange, blue You may assume that all are low-spin complexes (not strictly true in one case, but it doesn't change the answer)Explanation / Answer
Spectrochemical series : F- < H2O < NH3 < CN-
CN- is a strong field -acceptor ligand => low spin [Co(CN)6]3- complex (no unpaired electrons) => highest o => absorps in UV region => appears colorless
F- is a weak-field -donor ligand => high spin [CoF6]3- complex (4 unpaired electrons) => lowest o => absorps red => appears green
NH3 is a -donor ligand => low spin [Co(NH3)6]3+ complex => higher o than [Co(H2O)6]3+ => absorps in blue region => appears orange
H2O is a -donor ligand => low spin [Co(H2O)6]3+ complex => lower o than [Co(NH3)6]3+ => absorps in orange region => appears blue
Thus the beakers have colorless, green, orange and blue solutions contained CN-, F-, NH3 and H2O ligands resepectively.
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