Introduction
Base adsorption and minim/gram factors are key topics in pharmaceutics, linking surface chemistry with dosage calculation and drug formulation. This introduction covers adsorption mechanisms, isotherms (Langmuir, Freundlich), adsorption capacity (mg/g), kinetics, thermodynamics, and practical minim/gram considerations for measuring liquid volumes relative to powder mass. Understanding parameters such as Qe, Qmax, adsorption coefficient, contact time, pH effect and surface area helps B. Pharm students predict drug–adsorbent interactions, optimize formulations, and interpret lab adsorption data. Emphasis on unit conversions, dose expressions (minim per gram) and calculation methods prepares students for both theoretical exams and practical lab work. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. Which equation represents the Langmuir adsorption isotherm in its common linearized form?
- Qe = Kf Ce^(1/n)
- Qe = (Qmax b Ce) / (1 + b Ce)
- 1/Qe = 1/(Qmax b) × 1/Ce + 1/Qmax
- Log Qe = Log K + (1/n) Log Ce
Correct Answer: 1/Qe = 1/(Qmax b) × 1/Ce + 1/Qmax
Q2. In adsorption studies, Qe (adsorption capacity) is commonly calculated using which formula?
- Qe = (C0 – Ce) × V / m
- Qe = Ce / C0
- Qe = m / V
- Qe = K × Ce^(1/n)
Correct Answer: Qe = (C0 – Ce) × V / m
Q3. The Freundlich isotherm is best described as:
- A monolayer adsorption model on homogeneous sites
- An empirical model for heterogeneous surface adsorption
- A kinetic model describing adsorption rate
- A thermodynamic expression for ΔG only
Correct Answer: An empirical model for heterogeneous surface adsorption
Q4. Which parameter from the Langmuir model represents maximum monolayer adsorption capacity?
- b (Langmuir constant)
- Qe (adsorption at equilibrium)
- Qmax (maximum adsorption capacity)
- n (Freundlich exponent)
Correct Answer: Qmax (maximum adsorption capacity)
Q5. In Freundlich equation Log Qe = Log Kf + (1/n) Log Ce, the value of 1/n indicates:
- Adsorption capacity in mg/g
- Adsorption intensity or surface heterogeneity
- Rate constant of adsorption
- Monolayer coverage
Correct Answer: Adsorption intensity or surface heterogeneity
Q6. Which factor most commonly increases adsorption of an ionizable drug onto an adsorbent?
- pH causing drug to be in the ionized form when adsorbent prefers neutral form
- Decreased surface area of adsorbent
- Drug–adsorbent favorable electrostatic attraction at the solution pH
- Increased temperature always for physical adsorption
Correct Answer: Drug–adsorbent favorable electrostatic attraction at the solution pH
Q7. Which kinetic model assumes adsorption rate is proportional to square of unoccupied sites and often fits chemisorption?
- Pseudo-first-order kinetic model
- Pseudo-second-order kinetic model
- Intraparticle diffusion model only
- Elovich model exclusively for physical adsorption
Correct Answer: Pseudo-second-order kinetic model
Q8. The unit mg/g commonly used for adsorption capacity denotes:
- Mass of adsorbent per unit volume of solution
- Milligrams of adsorbate adsorbed per gram of adsorbent
- Milliliters of solution per gram of adsorbent
- Minims per gram
Correct Answer: Milligrams of adsorbate adsorbed per gram of adsorbent
Q9. In batch adsorption experiments, increasing adsorbent dose typically results in:
- Higher Qe (mg/g) always
- Lower percentage removal
- Higher total removal (%) but lower Qe (mg/g) due to unsaturated sites
- No change in adsorption behavior
Correct Answer: Higher total removal (%) but lower Qe (mg/g) due to unsaturated sites
Q10. Which thermodynamic sign indicates a spontaneous adsorption process at given temperature?
- ΔG positive
- ΔG negative
- ΔH positive always
- ΔS negative always
Correct Answer: ΔG negative
Q11. The term “minim” in pharmacy historically refers to:
- A unit of mass equal to 1/1000 gram
- A small unit of volume historically used in liquid dosing
- A measure of surface area
- A unit of pressure in dissolution testing
Correct Answer: A small unit of volume historically used in liquid dosing
Q12. Which conversion relationship among apothecaries’ units is correct?
- 1 fluid dram = 480 minims
- 1 fluid ounce = 60 minims
- 1 fluid dram = 60 minims
- 1 pint = 60 minims
Correct Answer: 1 fluid dram = 60 minims
Q13. If a formulation expresses a liquid drug as “minim per gram” of powder, this most likely indicates:
- Volume of liquid (in minims) required per gram of powder for wetting or granulation
- Mass of powder per minim of liquid
- Adsorption capacity in mg/g
- Surface area expressed in minims
Correct Answer: Volume of liquid (in minims) required per gram of powder for wetting or granulation
Q14. The dimensionless separation factor RL for Langmuir isotherm indicates favorability; RL between 0 and 1 suggests:
- Unfavorable adsorption
- Linear adsorption
- Favorable adsorption
- Irreversible adsorption
Correct Answer: Favorable adsorption
Q15. Intraparticle diffusion as rate-limiting step is typically identified when:
- Plot of Qt vs. t is a straight line through origin
- Plot of Qt vs. t^0.5 is linear but does not pass through origin
- Langmuir model fits perfectly
- Freundlich exponent n = 1
Correct Answer: Plot of Qt vs. t^0.5 is linear but does not pass through origin
Q16. Which experimental method is commonly used to determine Ce (equilibrium concentration) in adsorption studies?
- UV-visible spectrophotometry
- Mass spectrometry without calibration
- Visual turbidity only
- pH measurement exclusively
Correct Answer: UV-visible spectrophotometry
Q17. Chemical adsorption (chemisorption) differs from physical adsorption by:
- Weaker van der Waals forces only
- Formation of chemical bonds and higher activation energy
- Being fully reversible in all cases
- Occurring only at very low temperatures
Correct Answer: Formation of chemical bonds and higher activation energy
Q18. For the Langmuir constant b, a higher value usually indicates:
- Lower affinity between adsorbate and adsorbent
- Higher adsorption affinity
- Greater surface heterogeneity
- Smaller Qmax always
Correct Answer: Higher adsorption affinity
Q19. When temperature increases, physical adsorption is generally expected to:
- Increase due to exothermic nature
- Decrease because physical adsorption is exothermic
- Be independent of temperature
- Always convert to chemisorption
Correct Answer: Decrease because physical adsorption is exothermic
Q20. Which is a correct linear form of Freundlich isotherm for data plotting?
- 1/Qe vs. 1/Ce
- Log Qe vs. Log Ce
- Qe vs. Ce^2
- Ce vs. Qe/Ce
Correct Answer: Log Qe vs. Log Ce
Q21. A high specific surface area of an adsorbent usually results in:
- Lower adsorption capacity per unit mass
- Higher adsorption capacity per unit mass
- No effect on adsorption
- Only increased chemical reactivity, not adsorption
Correct Answer: Higher adsorption capacity per unit mass
Q22. Competitive adsorption in multi-component solutions most often leads to:
- Independent adsorption of each solute as in single-solute systems
- Preferential adsorption of one solute and reduced adsorption of others
- Increase in total adsorption capacity proportionally
- Elimination of adsorption entirely
Correct Answer: Preferential adsorption of one solute and reduced adsorption of others
Q23. The practical use of minim/gram factors in formulation is primarily for:
- Describing ionic strength of solutions
- Specifying volume of liquid excipient per gram of powder
- Measuring surface charge density
- Expressing adsorption isotherm constants
Correct Answer: Specifying volume of liquid excipient per gram of powder
Q24. Which plot would you generate to obtain Qmax and b from Langmuir data?
- Plot Ce vs. Qe
- Plot 1/Qe vs. 1/Ce
- Plot Qe vs. Log Ce
- Plot Qt vs. t
Correct Answer: Plot 1/Qe vs. 1/Ce
Q25. In adsorption equilibrium studies, an increase in solution ionic strength often:
- Has no effect on ionic adsorbates
- May reduce adsorption of charged species due to competition or shielding
- Always increases adsorption by compressing double layer
- Converts Freundlich to Langmuir behavior
Correct Answer: May reduce adsorption of charged species due to competition or shielding
Q26. The constant Kf in Freundlich isotherm is related to:
- Freundlich adsorption capacity at unit concentration
- Maximum monolayer capacity
- Rate of adsorption
- Only temperature sensitivity
Correct Answer: Freundlich adsorption capacity at unit concentration
Q27. If experimental data fit both Langmuir and Freundlich models, the likely interpretation is:
- Adsorption is strictly monolayer on homogeneous sites
- Data quality is poor and models are invalid
- System may show combined features; use best-fit statistics to choose model
- Neither physical nor chemical adsorption occurs
Correct Answer: System may show combined features; use best-fit statistics to choose model
Q28. The initial slope of adsorption isotherm at low concentration gives insight into:
- Maximum capacity only
- Adsorbent affinity for the adsorbate at low concentration
- The intraparticle diffusion coefficient
- Particle size distribution
Correct Answer: Adsorbent affinity for the adsorbate at low concentration
Q29. Which statement about adsorption reversibility is correct?
- Physisorption is usually reversible while chemisorption is often irreversible
- Chemisorption is always reversible
- Physisorption is always irreversible
- Both types are equally irreversible
Correct Answer: Physisorption is usually reversible while chemisorption is often irreversible
Q30. When reporting adsorption results for B. Pharm lab reports, which combination is most appropriate?
- Provide only raw absorbance values without conversions
- Report Qe (mg/g), isotherm parameters (Qmax, b, Kf, n), experimental conditions and minim/gram practical details if relevant
- Use only minim units and avoid mg/g
- Omit pH, temperature and contact time as they are irrelevant
Correct Answer: Report Qe (mg/g), isotherm parameters (Qmax, b, Kf, n), experimental conditions and minim/gram practical details if relevant
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.
Mail- Sachin@pharmacyfreak.com