Distillation of volatile oils MCQs With Answer is an essential topic in pharmacognosy for B. Pharm students focusing on extraction, purification, and characterization of essential oils. This introduction covers principles of steam, hydrodistillation and dry distillation, co‑distillation, azeotrope behavior, apparatus such as Clevenger and Likens‑Nickerson, factors affecting yield, and quality control parameters like specific gravity, refractive index, optical rotation and chromatographic profiling. Understanding thermal stability, solubility, and chemical composition (monoterpenes, sesquiterpenes, phenylpropanoids) helps optimize extraction and ensure therapeutic quality. Practical knowledge of safety, storage and analytical verification is emphasized. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. Which principle best describes steam distillation of volatile oils?
- Co‑distillation of immiscible liquids at a temperature below their boiling points
- Simple evaporation of oils at room temperature
- Solvent extraction using nonpolar solvents
- Fractional distillation under high pressure
Correct Answer: Co‑distillation of immiscible liquids at a temperature below their boiling points
Q2. The Clevenger apparatus is primarily designed for which purpose?
- Quantitative recovery of volatile oils by hydrodistillation
- High‑performance liquid chromatography of oils
- Steam sterilization of glassware
- Drying of crude drug powders
Correct Answer: Quantitative recovery of volatile oils by hydrodistillation
Q3. Hydrodistillation differs from steam distillation in that hydrodistillation:
- Involves immersion of plant material directly in boiling water
- Always uses superheated steam passed through a separate chamber
- Requires organic solvents to release oils
- Operates under vacuum exclusively
Correct Answer: Involves immersion of plant material directly in boiling water
Q4. Which factor does NOT significantly affect yield of volatile oil during distillation?
- Particle size of plant material
- Distillation time and temperature
- Brewing yeast strain used
- Moisture content of plant material
Correct Answer: Brewing yeast strain used
Q5. Co‑distillation implies:
- Distillation of volatile components with water vapor
- Use of two organic solvents to extract oils
- Distillation under elevated pressure only
- Fractional condensation by cooling towers
Correct Answer: Distillation of volatile components with water vapor
Q6. An azeotrope relevant to volatile oils refers to:
- A mixture of oil and water that boils at constant composition
- A purification technique using adsorption columns
- The solid residue after distillation
- A solvent used to dilute volatile oils
Correct Answer: A mixture of oil and water that boils at constant composition
Q7. Which compound class typically constitutes the major fraction of essential oils?
- Monoterpenes
- Alkaloids
- Polysaccharides
- Proteins
Correct Answer: Monoterpenes
Q8. Likens‑Nickerson apparatus is specially used for:
- Simultaneous distillation–extraction to isolate volatile components
- Measuring refractive index of oils
- Dry distillation of resins
- GC–MS calibration
Correct Answer: Simultaneous distillation–extraction to isolate volatile components
Q9. Why is vacuum distillation sometimes employed for volatile oils?
- To lower boiling points and prevent thermal degradation
- To increase water content in the oil
- To crystallize high molecular weight terpenes
- To enhance polymerization reactions
Correct Answer: To lower boiling points and prevent thermal degradation
Q10. Which quality control parameter helps detect oxidation or adulteration of essential oils?
- Specific gravity, refractive index and optical rotation
- Total ash value
- pH of the oil
- Moisture sorption isotherm
Correct Answer: Specific gravity, refractive index and optical rotation
Q11. Steam distillation of fresh leaves yields different profile than dried leaves because:
- Enzymatic and volatile component changes occur during drying
- Fresh leaves have higher polysaccharide content
- Dried leaves always produce higher moisture
- Only dried leaves allow co‑distillation
Correct Answer: Enzymatic and volatile component changes occur during drying
Q12. Which statement about solvent extraction versus distillation for volatile oils is true?
- Solvent extraction can recover non‑volatile odorants missed by steam distillation
- Distillation is always superior to solvent extraction in yield
- Solvent extraction does not require removal of solvent residues
- Distillation captures high molecular weight fixed oils preferentially
Correct Answer: Solvent extraction can recover non‑volatile odorants missed by steam distillation
Q13. During Clevenger hydrodistillation, the oily layer is collected because:
- Oil and water are immiscible and separate by density in the receiver
- The oil dissolves completely in water and is later precipitated
- Oil polymerizes into solid beads
- Oil reacts chemically with glass to form a product
Correct Answer: Oil and water are immiscible and separate by density in the receiver
Q14. Which constituent is most likely to be lost by prolonged heating during distillation?
- Highly volatile monoterpenes such as alpha‑pinene
- Inorganic salts
- Fixed triglyceride oils
- Cellulose fibers
Correct Answer: Highly volatile monoterpenes such as alpha‑pinene
Q15. Refractive index measurement of an essential oil helps to assess:
- Purity and presence of adulterants
- Color intensity only
- pH level in aqueous solution
- Antimicrobial potency
Correct Answer: Purity and presence of adulterants
Q16. Which analytical technique is most commonly used to profile components of distilled volatile oils?
- Gas chromatography–mass spectrometry (GC–MS)
- UV–visible spectrophotometry
- Flame photometry
- Osmometry
Correct Answer: Gas chromatography–mass spectrometry (GC–MS)
Q17. Optical rotation measurement of an essential oil is important because it:
- Indicates stereochemical composition and can signal adulteration
- Measures the oil’s boiling point
- Quantifies water content directly
- Determines color stability
Correct Answer: Indicates stereochemical composition and can signal adulteration
Q18. Which safety consideration is critical during steam distillation of volatile oils?
- Proper venting and prevention of pressure buildup to avoid explosions
- Use of edible solvents only
- Maintaining a basic pH above 10
- Sterilization of the oil at 121°C for 20 minutes
Correct Answer: Proper venting and prevention of pressure buildup to avoid explosions
Q19. The term ‘fractional distillation’ in context of volatile oils refers to:
- Separating oil components based on differing boiling ranges using fractionating column
- Removal of water by drying agents only
- Distillation of oils at room temperature
- Using chromatography to remove impurities
Correct Answer: Separating oil components based on differing boiling ranges using fractionating column
Q20. What role does pH play during hydrodistillation of certain plant materials?
- Acidic or alkaline conditions can hydrolyze some constituents altering oil composition
- pH has no influence on volatile oil composition
- Only neutral pH yields any oil at all
- Lower pH increases polymerization of terpenes into solids
Correct Answer: Acidic or alkaline conditions can hydrolyze some constituents altering oil composition
Q21. Which storage condition best preserves the quality of distilled volatile oils?
- Dark, cool, airtight amber glass containers
- Transparent plastic bottles at room temperature under light
- Open jars in humid environment
- Frequent exposure to air to maintain freshness
Correct Answer: Dark, cool, airtight amber glass containers
Q22. Which plant part typically yields the highest content of volatile oil by distillation?
- Flowers and leaves of aromatic species (varies by plant)
- Roots universally in all plants
- Wood core of all trees
- Seeds never contain volatile oils
Correct Answer: Flowers and leaves of aromatic species (varies by plant)
Q23. During distillation, the use of a condenser is necessary to:
- Condense vaporized oil‑water mixture back to liquid for collection
- Increase vapor temperature indefinitely
- Filter solid particles from the oil
- React chemically with the oil to form esters
Correct Answer: Condense vaporized oil‑water mixture back to liquid for collection
Q24. Which term describes the quantity of oil obtained per unit weight of plant material?
- Yield (w/w or v/w percentage)
- Specific rotation
- Partition coefficient
- Viscosity index
Correct Answer: Yield (w/w or v/w percentage)
Q25. Which of the following is a common sign of adulteration in citrus essential oils?
- Unexpectedly low limonene content and altered refractive index
- Higher water content only without any spectral changes
- Increased viscosity to that of fixed oils
- Presence of cellulose fibers
Correct Answer: Unexpectedly low limonene content and altered refractive index
Q26. Which pretreatment can increase volatile oil yield during distillation?
- Cell disruption by grinding to optimal particle size
- Adding sodium chloride to the plant material
- Freezing the plant material solid without thawing
- Complete dehydration to bone dry state
Correct Answer: Cell disruption by grinding to optimal particle size
Q27. What is the primary disadvantage of solvent extraction for obtaining aromatic concentrates compared to steam distillation?
- Possible solvent residues and need for solvent removal
- Inability to extract non‑volatile components
- Lower aromatic intensity always
- No requirement for analytical testing thereafter
Correct Answer: Possible solvent residues and need for solvent removal
Q28. Which parameter measured after distillation indicates the concentration of a volatile oil relative to water?
- Specific gravity (relative density)
- Total ash value
- Moisture content by loss on drying
- Acid insoluble ash
Correct Answer: Specific gravity (relative density)
Q29. Sesquiterpenes in essential oils are generally characterized by:
- Higher molecular weight and lower volatility than monoterpenes
- Being completely miscible with water
- Always being phenolic compounds
- Having no role in aroma
Correct Answer: Higher molecular weight and lower volatility than monoterpenes
Q30. Which practice is recommended to reduce oxidative degradation of distilled volatile oils?
- Addition of inert gas (nitrogen) headspace and antioxidant as needed
- Storing oil at high temperature to prevent condensation
- Continuous exposure to light to maintain activity
- Frequent opening of container to refresh air
Correct Answer: Addition of inert gas (nitrogen) headspace and antioxidant as needed
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