MChem Master of Chemistry Materials Chemistry 1 — Questions and Answers
Question 1: What defines a zeolite's selectivity as a molecular sieve or catalyst?
- Its high surface area and amorphous structure
- Its regular microporous aluminosilicate framework with defined pore sizes (Correct answer)
- Its high iron content enabling redox catalysis
- Its layered graphene-like structure
Correct answer: Its regular microporous aluminosilicate framework with defined pore sizes
Zeolites are crystalline aluminosilicates with uniform micropores (3–10 Å) that selectively admit molecules by size and shape, making them ideal sieves and acid catalysts.
Question 2: What is the key characteristic of a thermosetting polymer compared to a thermoplastic polymer?
- Thermosets can be remolded repeatedly upon heating
- Thermosets form irreversible cross-linked networks during curing and cannot be remelted (Correct answer)
- Thermosets have lower molecular weight than thermoplastics
- Thermosets are always crystalline, while thermoplastics are amorphous
Correct answer: Thermosets form irreversible cross-linked networks during curing and cannot be remelted
Thermosetting polymers (epoxies, phenolics) form covalent cross-links during curing, creating an infusible, insoluble network that cannot be reprocessed.
Question 3: In the context of nanomaterials, what phenomenon explains why gold nanoparticles appear red/purple rather than gold-colored?
- Quantum confinement of electrons
- Localized surface plasmon resonance (LSPR) (Correct answer)
- Band gap widening at the nanoscale
- Rayleigh scattering of blue light
Correct answer: Localized surface plasmon resonance (LSPR)
LSPR occurs when the collective oscillation of conduction electrons in gold nanoparticles resonantly absorbs visible light (~520 nm), producing red/purple color.
Question 4: What is the role of a surfactant in the synthesis of mesoporous silica materials (e.g., MCM-41)?
- It acts as a reducing agent for silica formation
- It serves as a structure-directing template around which silica condenses (Correct answer)
- It increases the surface tension of the reaction mixture
- It provides silicon atoms for framework construction
Correct answer: It serves as a structure-directing template around which silica condenses
Surfactant micelles act as structure-directing agents; silica condenses around them, and template removal (calcination) leaves ordered mesopores with high surface area.
Question 5: What distinguishes Type II superconductors from Type I superconductors?
- Type II have higher resistivity than Type I at all temperatures
- Type II allow partial magnetic flux penetration in the mixed state between two critical fields (Correct answer)
- Type II superconductors operate only below 4 K
- Type II exhibit the Meissner effect only above Tc
Correct answer: Type II allow partial magnetic flux penetration in the mixed state between two critical fields
Type II superconductors have two critical fields (Hc1 and Hc2); between them, magnetic flux penetrates as quantized vortices, enabling their use at higher fields.
Question 6: In sol-gel chemistry, what reaction converts metal alkoxide precursors into a metal oxide network?
- Reduction followed by precipitation
- Hydrolysis and condensation polymerization (Correct answer)
- Thermal decomposition at high temperature
- Electrolytic oxidation of metal salts
Correct answer: Hydrolysis and condensation polymerization
Metal alkoxides (e.g., TEOS for silica) undergo hydrolysis to form silanols, which then condense via Si–O–Si bond formation to build an amorphous oxide network.
MChem Master of Chemistry Materials Chemistry 1
What defines a zeolite's selectivity as a molecular sieve or catalyst?