MChem Master of Chemistry Master of Chemistry: Inorganic Chemistry 3 — Questions and Answers
Question 1: Which of the following is an example of a hypervalent compound that violates the octet rule?
- BF₃
- NH₃
- PCl₅ (Correct answer)
- H₂O
Correct answer: PCl₅
PCl₅ has 10 electrons around phosphorus (5 bonding pairs), making it a hypervalent molecule that invokes d-orbital or 3-center bonding descriptions.
Question 2: The 18-electron rule predicts that which of the following complexes is coordinatively unsaturated?
- [Cr(CO)₆]
- [Fe(CO)₅]
- [Mn(CO)₅]⁺
- [V(CO)₆] (Correct answer)
Correct answer: [V(CO)₆]
V has 5 valence electrons; six CO ligands donate 12 electrons, giving 17 total electrons—one short of the 18-electron count, making [V(CO)₆] coordinatively unsaturated.
Question 3: In solid-state chemistry, the rock salt structure adopted by NaCl can be described as:
- Na⁺ in tetrahedral holes of an FCC Cl⁻ lattice
- Na⁺ in octahedral holes of an FCC Cl⁻ lattice (Correct answer)
- Na⁺ in tetrahedral holes of a BCC Cl⁻ lattice
- Na⁺ in trigonal prismatic holes of an HCP Cl⁻ lattice
Correct answer: Na⁺ in octahedral holes of an FCC Cl⁻ lattice
In NaCl, Cl⁻ ions form an FCC lattice and Na⁺ ions occupy all octahedral holes, giving each ion a coordination number of 6.
Question 4: Which property distinguishes a Type II (high-Tc) superconductor from a Type I superconductor?
- Type II has a single critical field (Hc) below which it is fully diamagnetic
- Type II exhibits two critical fields (Hc1 and Hc2) with a mixed Abrikosov vortex state between them (Correct answer)
- Type II superconductors only occur in pure elemental metals
- Type II shows the Meissner effect only above Tc
Correct answer: Type II exhibits two critical fields (Hc1 and Hc2) with a mixed Abrikosov vortex state between them
Type II superconductors have two critical fields: below Hc1 full Meissner effect operates, between Hc1 and Hc2 magnetic flux penetrates as vortices, and above Hc2 superconductivity is lost.
Question 5: In VSEPR theory, which molecular geometry results from an AX₄E₂ electron domain arrangement?
- Octahedral
- Square pyramidal
- Square planar (Correct answer)
- Trigonal bipyramidal
Correct answer: Square planar
AX₄E₂ has 6 electron domains (4 bonding + 2 lone pairs) arranged octahedrally; the two lone pairs occupy axial positions, giving a square planar molecular geometry.
Question 6: The Kapustinskii equation is used to estimate which thermodynamic quantity?
- Gibbs energy of hydration of ions
- Lattice enthalpy of ionic compounds (Correct answer)
- Entropy of fusion of ionic solids
- Ionization energy of transition metals
Correct answer: Lattice enthalpy of ionic compounds
The Kapustinskii equation approximates lattice enthalpy from the number of ions, their charges, and the sum of ionic radii without requiring the full crystal structure.
Question 7: Which spectroscopic method directly probes the oxidation state and local coordination environment of a metal in a heterogeneous catalyst?
- UV-Vis diffuse reflectance spectroscopy
- X-ray absorption spectroscopy (XANES/EXAFS) (Correct answer)
- Raman spectroscopy
- Electron paramagnetic resonance (EPR)
Correct answer: X-ray absorption spectroscopy (XANES/EXAFS)
XANES gives oxidation state information via edge energy, while EXAFS provides local coordination number, bond distances, and identity of neighbors around the absorbing metal.
MChem Master of Chemistry Master of Chemistry: Inorganic Chemistry 3
Which of the following is an example of a hypervalent compound that violates the octet rule?