Hydrolysis MCQs With Answer
Hydrolysis is a central concept for B. Pharm students, covering mechanisms, kinetics, and pharmaceutical implications such as drug stability, ester hydrolysis, amide hydrolysis, acid-base catalysis, and enzymatic hydrolysis. This introduction highlights key terms like pH-rate profile, pseudo-first-order kinetics, buffer catalysis, prodrug activation, and aqueous degradation pathways. Understanding factors that influence hydrolytic rates — including temperature, ionic strength, neighboring group participation, and leaving-group ability — is essential for formulation, stability testing, and rational prodrug design. These MCQs deepen conceptual and problem-solving skills relevant to pharmaceutical chemistry and drug development. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. What is hydrolysis in the context of pharmaceutical chemistry?
- Oxidation of drug molecules by oxygen
- Cleavage of a bond by reaction with water, including ester and amide hydrolysis
- Conversion of a drug into an insoluble salt
- Formation of a complex with metal ions
Correct Answer: Cleavage of a bond by reaction with water, including ester and amide hydrolysis
Q2. Under conditions where water concentration is effectively constant, hydrolytic reactions typically follow which kinetics?
- Second-order kinetics with respect to water
- Pseudo-first-order kinetics with respect to substrate
- Zero-order kinetics in all reactants
- Mixed-order kinetics that cannot be simplified
Correct Answer: Pseudo-first-order kinetics with respect to substrate
Q3. Which functional group generally hydrolyzes faster under comparable conditions?
- Amides
- Esters
- Ketones
- Alcohols
Correct Answer: Esters
Q4. How does acid catalysis accelerate carbonyl hydrolysis?
- By deprotonating water to form a stronger nucleophile
- By protonating the carbonyl oxygen, increasing electrophilicity of the carbonyl carbon
- By forming a covalent bond between buffer and substrate
- By irreversibly converting substrate into an inactive complex
Correct Answer: By protonating the carbonyl oxygen, increasing electrophilicity of the carbonyl carbon
Q5. In a log k versus pH profile, a slope of +1 generally indicates which catalytic mode?
- Specific acid catalysis
- Specific base catalysis
- General acid catalysis
- No catalytic involvement
Correct Answer: Specific base catalysis
Q6. The mechanism of base-catalyzed ester hydrolysis proceeds by which pathway?
- Radical chain reaction
- Bimolecular nucleophilic acyl substitution via a tetrahedral intermediate
- SN1-like carbocation formation at the alkyl side
- Concerted pericyclic rearrangement
Correct Answer: Bimolecular nucleophilic acyl substitution via a tetrahedral intermediate
Q7. Why are amides generally more resistant to hydrolysis than esters?
- Amides form stronger hydrogen bonds with water
- Resonance delocalization between the nitrogen lone pair and the carbonyl reduces carbonyl electrophilicity
- Amides have larger steric bulk around the carbonyl
- Amides cannot form tetrahedral intermediates
Correct Answer: Resonance delocalization between the nitrogen lone pair and the carbonyl reduces carbonyl electrophilicity
Q8. Under pseudo-first-order conditions, the half-life (t1/2) of hydrolysis is:
- Directly proportional to initial substrate concentration
- Independent of initial substrate concentration and equal to ln2/kobs
- Dependent on water concentration only
- Equal to the activation energy divided by temperature
Correct Answer: Independent of initial substrate concentration and equal to ln2/kobs
Q9. Which experimental observation indicates general acid-base catalysis rather than specific catalysis?
- Rate is independent of buffer concentration at constant pH
- Rate varies with buffer concentration at constant pH
- Rate changes only with ionic strength
- Rate depends solely on temperature
Correct Answer: Rate varies with buffer concentration at constant pH
Q10. What is neighboring group participation in hydrolysis?
- Solvent molecules forming micelles around the substrate
- An intramolecular nucleophile assisting formation of cyclic intermediates that accelerate hydrolysis
- Buffer ions neutralizing the substrate surface charge
- Hydrophobic interactions that slow water access
Correct Answer: An intramolecular nucleophile assisting formation of cyclic intermediates that accelerate hydrolysis
Q11. Which statement best describes ester prodrugs used in pharmaceutics?
- They are designed to resist enzymatic hydrolysis indefinitely
- They are hydrolyzed by esterases in vivo to release the active parent drug
- They always convert to toxic metabolites on hydrolysis
- They only undergo acid-catalyzed hydrolysis in the stomach
Correct Answer: They are hydrolyzed by esterases in vivo to release the active parent drug
Q12. According to the Arrhenius equation, how does hydrolysis rate change with temperature?
- Rate decreases linearly with temperature
- Rate increases exponentially with temperature; activation energy can be obtained from ln k versus 1/T
- Rate is independent of temperature if pH is constant
- Rate is inversely proportional to activation energy
Correct Answer: Rate increases exponentially with temperature; activation energy can be obtained from ln k versus 1/T
Q13. How does ionic strength commonly influence hydrolysis rates?
- Ionic strength never affects hydrolysis reactions
- Ionic strength affects rates when charged reactants or transition states are involved by screening electrostatic interactions
- Ionic strength only affects reactions in non-aqueous solvents
- Ionic strength increases solvent viscosity, which always stops hydrolysis
Correct Answer: Ionic strength affects rates when charged reactants or transition states are involved by screening electrostatic interactions
Q14. How can you experimentally demonstrate buffer catalysis of an ester hydrolysis?
- Measure rate at different pH values but constant buffer concentration
- Change buffer concentration at constant pH; a change in rate indicates buffer catalysis
- Keep all conditions constant and vary light exposure
- Only measure the reaction at extremely high temperature
Correct Answer: Change buffer concentration at constant pH; a change in rate indicates buffer catalysis
Q15. Which analytical technique is most commonly used to quantify hydrolysis and its products in drug stability studies?
- Polarimetry
- High-performance liquid chromatography (HPLC)
- Flame photometry
- Viscometry
Correct Answer: High-performance liquid chromatography (HPLC)
Q16. For formulation to enhance hydrolytic stability, which approach is commonly used?
- Store at pH near the substrate’s maximum hydrolysis rate
- Adjust and maintain pH to a region of minimal hydrolysis and control temperature
- Increase water content to saturate hydrolysis
- Expose formulation to sunlight to deactivate water
Correct Answer: Adjust and maintain pH to a region of minimal hydrolysis and control temperature
Q17. Which acyl functional group is most susceptible to hydrolysis under aqueous conditions?
- Amide
- Acid chloride
- Phenol
- Ether
Correct Answer: Acid chloride
Q18. Aspirin (acetylsalicylic acid) mainly undergoes hydrolysis in plasma by which enzyme class?
- Proteases
- Esterases
- Kinases
- Lipoxygenases
Correct Answer: Esterases
Q19. In a pH-rate profile, a slope of −1 in log k versus pH indicates which condition?
- Specific base catalysis
- Specific acid catalysis where rate ∝ [H+]⁻¹
- No pH dependence
- Buffer catalysis only
Correct Answer: Specific acid catalysis where rate ∝ [H+]⁻¹
Q20. When designing an ester prodrug for predictable hydrolysis in blood, which property is most important?
- Complete insolubility in aqueous media
- Known rate of esterase-catalyzed hydrolysis and appropriate lipophilicity for absorption
- High chemical reactivity toward air oxidation
- Ability to form strong chelates with metal ions
Correct Answer: Known rate of esterase-catalyzed hydrolysis and appropriate lipophilicity for absorption
Q21. A pronounced solvent isotope effect (rate in H2O vs D2O) suggests what about the rate-determining step?
- It does not involve proton transfer
- It involves proton transfer or hydrogen-bonding changes in the transition state
- It is diffusion-controlled only
- It is purely entropic with no bond changes
Correct Answer: It involves proton transfer or hydrogen-bonding changes in the transition state
Q22. For a simple first-order hydrolysis with rate constant k = 0.023 min⁻¹, what is the half-life?
- Approximately 0.03 minutes
- Approximately 30 minutes
- Approximately 3 minutes
- Approximately 23 minutes
Correct Answer: Approximately 30 minutes
Q23. How can metal ions act to catalyze hydrolysis of carbonyl compounds?
- By increasing solvent polarity dramatically
- By acting as Lewis acids to activate water or polarize the carbonyl for nucleophilic attack
- By reducing the substrate’s molecular weight
- By absorbing the product and preventing reaction
Correct Answer: By acting as Lewis acids to activate water or polarize the carbonyl for nucleophilic attack
Q24. Which lactone ring sizes typically hydrolyze faster due to ring strain?
- Five- and six-membered lactones
- Three- and four-membered lactones
- Large 12-membered lactones only
- Lactones do not hydrolyze in water
Correct Answer: Three- and four-membered lactones
Q25. How do electron-withdrawing substituents adjacent to a carbonyl affect hydrolysis?
- They decrease the rate by destabilizing the transition state
- They increase the rate by stabilizing positive charge in the transition state and enhancing electrophilicity
- They have no effect on hydrolysis
- They convert hydrolysis into a radical pathway
Correct Answer: They increase the rate by stabilizing positive charge in the transition state and enhancing electrophilicity
Q26. Which buffer anion can act as a nucleophilic catalyst for ester hydrolysis?
- Perchlorate
- Acetate
- Nitrate
- Helium
Correct Answer: Acetate
Q27. If a hydrolysis rate is first order in substrate and first order in hydroxide, the overall rate law is:
- Rate = k[substrate]
- Rate = k[OH-]
- Rate = k[substrate][OH-] (second-order overall)
- Rate = k[substrate]^2
Correct Answer: Rate = k[substrate][OH-] (second-order overall)
Q28. Which gastrointestinal condition favors acid-catalyzed hydrolysis of an oral drug?
- Neutral pH in the small intestine
- Highly basic pancreatic fluid
- Low pH in the stomach
- Presence of bile salts only
Correct Answer: Low pH in the stomach
Q29. How does the pKa of the leaving group affect hydrolysis rate?
- Lower pKa (better leaving group) increases hydrolysis rate
- Higher pKa always increases hydrolysis rate
- pKa of leaving group has no effect on hydrolysis
- Only steric factors matter, not pKa
Correct Answer: Lower pKa (better leaving group) increases hydrolysis rate
Q30. What is a standard approach in accelerated stability testing for hydrolytically labile drugs?
- Store at extremely low temperatures and dry conditions only
- Subject samples to elevated temperature and controlled humidity to predict long-term stability
- Expose samples to pure oxygen while keeping temperature constant
- Mix the drug with reactive metals to speed degradation
Correct Answer: Subject samples to elevated temperature and controlled humidity to predict long-term stability
