CPC Inorganic Chemistry & Coordination Compounds 1 — Questions and Answers
Question 1: What is the coordination number of the central metal ion in [Co(NH3)6]3+?
- 3
- 6 (Correct answer)
- 4
- 2
Correct answer: 6
The coordination number equals the number of ligands directly bonded to the central metal; in [Co(NH3)6]3+, six NH3 molecules coordinate to cobalt.
Question 2: Which of the following best describes a chelating ligand?
- A ligand that donates only one electron pair to the metal
- A ligand that binds to the metal at two or more donor atoms, forming a ring (Correct answer)
- A ligand that accepts electron pairs from the metal via backbonding
- A monodentate ligand with a high formal charge
Correct answer: A ligand that binds to the metal at two or more donor atoms, forming a ring
Chelating (polydentate) ligands coordinate through two or more donor atoms simultaneously, forming a ring structure with the metal center.
Question 3: What is the ground-state electron configuration of Fe2+?
- [Ar] 3d6 4s2
- [Ar] 3d5 4s1
- [Ar] 3d6 (Correct answer)
- [Ar] 3d4 4s2
Correct answer: [Ar] 3d6
Neutral Fe is [Ar] 3d6 4s2; losing two electrons removes the 4s electrons first, yielding [Ar] 3d6 for Fe2+.
Question 4: In an octahedral crystal field, which d-orbitals constitute the eg set?
- dxy and dx²−y²
- dxz and dyz
- dx²−y² and dz² (Correct answer)
- dxy and dz²
Correct answer: dx²−y² and dz²
The eg set (dx²−y² and dz²) points directly toward the six ligands along the axes and is destabilized more than the t2g set.
Question 5: What type of isomerism is exhibited by [Co(NH3)4Cl2]NO2 and [Co(NH3)4ClNO2]Cl?
- Geometric isomerism
- Optical isomerism
- Ionization isomerism (Correct answer)
- Linkage isomerism
Correct answer: Ionization isomerism
Ionization isomers produce different ions in solution; the first complex releases NO2− while the second releases Cl− as the counter ion.
Question 6: The color of transition metal coordination compounds arises primarily from which electronic transition?
- n→π* transitions
- d-d transitions (Correct answer)
- π→π* transitions
- f-f transitions
Correct answer: d-d transitions
Visible color in transition metal complexes typically results from d-d transitions, where electrons are promoted between crystal-field-split d-orbital levels.
Question 7: What is the oxidation state of manganese in KMnO4?
- +4
- +6
- +7 (Correct answer)
- +5
Correct answer: +7
With K at +1 and four oxygens at −2 each (total −8), the sum must equal zero, requiring Mn to be +7.
CPC Inorganic Chemistry & Coordination Compounds 1
What is the coordination number of the central metal ion in [Co(NH3)6]3+?