Introduction: The specific surface of powders, or specific surface area (SSA), is the surface area per unit mass of a powder and a vital parameter in pharmaceutical formulation. For B. Pharm students, understanding SSA, its units (m2/g), measurement methods (BET gas adsorption, permeability, microscopy), and its relation to particle size, porosity, wetting, dissolution rate and surface energy is essential for predicting drug bioavailability, stability and processing behaviour. Practical considerations include sample preparation, degassing, pore contribution and shape factors. Mastery of these concepts helps optimize dissolution, flowability and tablet strength. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. What is the correct definition of specific surface area (SSA) for powders?
- Surface area per unit volume of powder
- Surface area per unit mass of powder
- Total particle size per particle
- Surface roughness of a single particle
Correct Answer: Surface area per unit mass of powder
Q2. Which unit is most commonly used to express specific surface area in pharmaceutical sciences?
- m/s
- g/cm3
- m2/g
- µm
Correct Answer: m2/g
Q3. For non-porous spherical particles, which formula relates SSA (S), density (ρ) and diameter (D)?
- S = 3/(ρ·D)
- S = 6/(ρ·D)
- S = 4·π·D/(ρ)
- S = ρ·D/6
Correct Answer: S = 6/(ρ·D)
Q4. Which measurement technique is the standard for determining total surface area including micropores?
- Laser diffraction
- Gas adsorption using BET theory
- Optical microscopy
- Tap density
Correct Answer: Gas adsorption using BET theory
Q5. In BET analysis, nitrogen adsorption is commonly performed at which temperature?
- 25 °C (room temperature)
- 0 °C
- 77 K (liquid nitrogen temperature)
- 373 K (100 °C)
Correct Answer: 77 K (liquid nitrogen temperature)
Q6. Which surface is measured by BET for porous powders?
- Only the external surface of particles
- Only the external and accessible internal surface
- Only the surface of nonporous particles
- Electrical surface area, not physical surface
Correct Answer: Only the external and accessible internal surface
Q7. Which of the following best describes the role of SSA in dissolution rate according to Noyes–Whitney?
- Dissolution rate decreases with increasing SSA
- Dissolution rate is independent of SSA
- Dissolution rate increases with increasing SSA
- Dissolution rate depends only on solubility, not SSA
Correct Answer: Dissolution rate increases with increasing SSA
Q8. What is the main assumption of the BET model used for SSA determination?
- Adsorption occurs in a single monolayer only
- Adsorption occurs in multiple layers with uniform heat after the first layer
- Adsorption is purely chemical and irreversible
- Particles are always spherical and nonporous
Correct Answer: Adsorption occurs in multiple layers with uniform heat after the first layer
Q9. Which parameter obtained from BET analysis is directly used to calculate surface area?
- Monolayer adsorbed gas volume (vm)
- Langmuir constant (a)
- Particle size distribution
- Pore tortuosity
Correct Answer: Monolayer adsorbed gas volume (vm)
Q10. Which factor can cause an underestimation of SSA in gas adsorption measurements?
- Inadequate degassing leaving adsorbed contaminants
- Using a gas with too small molecular size
- Measuring at very low relative pressures only
- Using large sample mass
Correct Answer: Inadequate degassing leaving adsorbed contaminants
Q11. How does particle agglomeration affect measured SSA?
- Agglomeration increases measured SSA due to more contacts
- Agglomeration reduces measured SSA because internal surfaces become inaccessible
- Agglomeration does not affect SSA measurements
- Agglomeration converts SSA to particle density
Correct Answer: Agglomeration reduces measured SSA because internal surfaces become inaccessible
Q12. Which technique estimates SSA indirectly by measuring flow/permeability of air through a packed bed?
- Blaine air permeability method
- Mercury intrusion porosimetry
- Atomic force microscopy
- Fourier transform infrared spectroscopy
Correct Answer: Blaine air permeability method
Q13. Which statement is true about micropores and their contribution to SSA?
- Micropores (<2 nm) contribute little to SSA
- Micropores can contribute disproportionately large SSA
- Only mesopores contribute to SSA
- Macropores (<2 nm) are the main contributor
Correct Answer: Micropores can contribute disproportionately large SSA
Q14. Which preparation step is critical before BET measurement to obtain reproducible SSA?
- Wetting the sample with water
- Heat/treatment degassing to remove adsorbed species
- Grinding to change particle size
- Coating particles with gold
Correct Answer: Heat/treatment degassing to remove adsorbed species
Q15. High specific surface area in a drug powder most likely leads to which risk?
- Reduced chemical reactivity
- Increased risk of moisture uptake and chemical degradation
- Improved flowability always
- Lower dissolution rate
Correct Answer: Increased risk of moisture uptake and chemical degradation
Q16. Which property is NOT directly influenced by SSA in formulations?
- Dissolution rate
- Chemical reactivity
- Tablet hardness due to bonding area
- API intrinsic solubility
Correct Answer: API intrinsic solubility
Q17. A BET adsorption isotherm type II typically indicates what about the material?
- Nonporous or macroporous material with unrestricted monolayer–multilayer adsorption
- Primarily microporous material
- Material with closed pores inaccessible to gas
- Chemical adsorption only
Correct Answer: Nonporous or macroporous material with unrestricted monolayer–multilayer adsorption
Q18. Why is the choice of adsorbate gas important in SSA determination?
- Different gases have different molecular cross-sectional areas affecting SSA calculation
- Any gas gives identical results regardless of size
- Only reactive gases should be used to ensure bonding
- Gas choice affects particle density but not surface measurement
Correct Answer: Different gases have different molecular cross-sectional areas affecting SSA calculation
Q19. Which analytical method can visualize surface topography and help explain high SSA values?
- Scanning electron microscopy (SEM)
- Ultraviolet spectroscopy
- Mass spectrometry
- X-ray diffraction for crystal structure only
Correct Answer: Scanning electron microscopy (SEM)
Q20. If two powders have identical chemical composition and particle size distribution but different SSA, what is a likely reason?
- Different porosity or surface roughness
- Different color
- Different melting points
- Different bulk density only
Correct Answer: Different porosity or surface roughness
Q21. Which statement about BET c constant is correct?
- c reflects the heat of adsorption of the first layer relative to subsequent layers
- c measures particle size directly
- c is unrelated to adsorption energetics
- c equals the monolayer volume
Correct Answer: c reflects the heat of adsorption of the first layer relative to subsequent layers
Q22. Mercury intrusion porosimetry measures which property that can be related to SSA?
- Surface chemical composition
- Pore size distribution and pore volume
- Crystal lattice defects
- Adsorbed gas monolayer
Correct Answer: Pore size distribution and pore volume
Q23. How does SSA affect compaction and tablet strength?
- Higher SSA reduces bonding between particles and weakens tablets
- Higher SSA generally increases interparticle bonding and can improve tablet strength
- SSA has no influence on compaction
- Only lubricant concentration matters, not SSA
Correct Answer: Higher SSA generally increases interparticle bonding and can improve tablet strength
Q24. Which of the following is a limitation of laser diffraction for SSA estimation?
- It cannot measure particle size distribution
- It estimates surface area indirectly and may underestimate SSA of porous particles
- It directly measures pore surface area accurately
- It requires extremely high vacuum
Correct Answer: It estimates surface area indirectly and may underestimate SSA of porous particles
Q25. In BET theory plot linearization, which plot is commonly used to derive vm?
- Plot of P versus V
- Plot of 1/[V(P0/P − 1)] versus P/P0
- Plot of log V versus log P
- Plot of V versus P0
Correct Answer: Plot of 1/[V(P0/P − 1)] versus P/P0
Q26. Which practice will artificially increase apparent SSA measured by gas adsorption?
- Incomplete degassing before measurement
- Overheating that collapses porous structure
- Using a gas with too large molecular diameter
- Contaminant surface films blocking adsorption sites
Correct Answer: Contaminant surface films blocking adsorption sites
Q27. What is the effect of particle shape on calculated SSA using the sphere approximation?
- Shape has no effect; spheres represent all shapes accurately
- Non-spherical shapes require shape factors; sphere approximation can misestimate SSA
- Only density matters, shape is irrelevant
- Spherical approximation always underestimates true SSA
Correct Answer: Non-spherical shapes require shape factors; sphere approximation can misestimate SSA
Q28. Which of the following is true about external surface and internal surface in powders?
- External surface is always larger than internal surface
- Internal surface (pores) can dominate total SSA in porous materials
- Only external surface affects dissolution
- Internal surface is irrelevant for adsorption measurements
Correct Answer: Internal surface (pores) can dominate total SSA in porous materials
Q29. For formulation scientists, why is monitoring SSA during wet granulation important?
- SSA influences binder distribution, granule growth, dissolution and final tablet properties
- SSA remains constant during wet granulation and is irrelevant
- Only moisture content matters, not SSA
- SSA only affects color of granules
Correct Answer: SSA influences binder distribution, granule growth, dissolution and final tablet properties
Q30. Which combination of measurements gives the most complete understanding of powder surface characteristics?
- Only BET surface area measurement
- BLAINE permeability and tap density only
- BET surface area, pore size distribution (mercury porosimetry) and microscopy (SEM)
- Only particle color and odor assessment
Correct Answer: BET surface area, pore size distribution (mercury porosimetry) and microscopy (SEM)
I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.
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