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Dr. Woodward
Chemistry 123
Sample Quiz 1
Spring 2007
Quiz 5
20 Minutes
Name _____________________________________
Lab Inst. ___________
Two-Digit Section Number ___________
ALL WORK MUST BE SHOWN TO RECEIVE FULL CREDIT
1. The absorption maximum for the complex ion [Co(NH3)6]3+ occurs at 470 nm.
(a) [2 points] Predict the color of this complex. Orange
(b) [2 points] If the cobalt ion adopts a low spin
configuration draw the crystal-field energy-level
diagram and show the placement of the delectrons?
dx2-y2
dxy
dxz
dz2
dyz
(c) [4 points] Calculate the crystal field splitting energy, Δ, in eV.
E = hc/λ = (6.626 × 10–34 J-s)(3.00 × 108 m/s)/(470 × 10–9 m) = 4.23 × 10–19 J
E = (4.23 × 10–19 J) × (1 eV/1.602 × 10–19 J) = 2.64 eV
(d) [2 points] Would you expect the absorption maximum of [Co(H2O)6]3+ to fall at a longer
or at a shorter wavelength (assume low spin configuration is maintained)?
According to the spectrochemical series H2O is a weaker field ligand that NH3.
Therefore, the crystal field splitting Δ will be smaller and the absorption maximum
will be shifted to longer wavelengths.
2. [6 points] The following pictures show two molecular orbitals of the many that exist for a MoF6
molecule, which has octahedral geometry. For each MO, identify the atomic orbitals involved in
forming the molecular orbital (Mo 5s, 5p, 4d; F 2s, 2p), and classify the molecular orbital as
bonding, antibonding or non-bonding. [The Mo atom is at the center of the molecule, it is
surrounded by six fluorine atoms]
Error!
Mo 4d – O 2p
antibonding
O 2p
nonbonding
Q5-R 11:30
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3. Draw all stereoisomers (geometric and/or optical) for the following complexes:
(a) [4 points] octahedral [Co(NH)3Cl3]+
Two geometric isomers (fac- and mer-) as shown in problem 24.4 in the homework
exercises
(b) [4 points] square planar [PdBr2Cl2]2–
Two geometric isomers, cis- and trans-
4. [3 points] The figure below shows the absorption spectra for a transition metal complex
[M(NH3)6]2+ (where M is a transition metal ion). What would be the color of this complex? How
would the absorption peak at ~610 nm shift if the NH3 ligands were replaced with H2O?
2.0
1.8
1.6
absorbance
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
200
300
400
500
600
700
800
900
wavelength (nm)
This compound absorbs strongly yellow, orange and red light. Therefore it will appear to
the middle color of the remaining colors (violet, blue, green), so it’s color will be blue [this is
the [Cu(NH3)6]2+ discussed in the lab manual]
If the NH3 ligands are replaced with H2O the crystal field splitting will get smaller and the
absorption maximum will shift to longer wavelengths [see spectrum in the lab manual]
Q5-R 11:30
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