Introduction: The “Isolation of caffeine from tea dust MCQs With Answer” is a concise, practice-focused resource designed for B.Pharm students studying pharmacognosy and pharmaceutical analysis. It concentrates on practical extraction techniques—defatting, hot water extraction, basification, solvent extraction (chloroform/dichloromethane/ethyl acetate), Soxhlet use, recrystallization and analytical checks such as TLC, UV spectrophotometry (λmax ≈ 273 nm), melting point and IR. Keywords include caffeine isolation, tea dust, alkaloid extraction, solvent extraction, recrystallization, partition coefficient, and purity testing. This set highlights safety, common pitfalls and interpretation of results. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. Which structural name correctly describes caffeine?
- 1,3,7-Trimethylxanthine
- 1,5-Dimethylbarbituric acid
- Catecholamine derivative
- Phenothiazine analogue
Correct Answer: 1,3,7-Trimethylxanthine
Q2. What is the molecular formula of caffeine?
- C7H8N4O2
- C8H10N4O2
- C9H12N4O3
- C6H6N2O
Correct Answer: C8H10N4O2
Q3. Which solvent is commonly used to extract free-base caffeine from basified aqueous tea extract?
- Petroleum ether
- Dichloromethane (methylene chloride)
- Ethylene glycol
- Water
Correct Answer: Dichloromethane (methylene chloride)
Q4. What is the primary purpose of defatting tea dust with petroleum ether before caffeine extraction?
- Remove caffeine first
- Eliminate nonpolar lipids and pigments that interfere with extraction
- Hydrolyze glycosides
- Neutralize acidic components
Correct Answer: Eliminate nonpolar lipids and pigments that interfere with extraction
Q5. Which step converts caffeine salts in tea infusion to extractable free caffeine?
- Acidification with dilute HCl
- Basification with ammonia or NaOH
- Heating to 100°C without pH change
- Adding sodium sulfate
Correct Answer: Basification with ammonia or NaOH
Q6. Which analytical method gives a quick quantitative estimate of caffeine in the extract by measuring absorbance at about 273 nm?
- Infrared spectroscopy
- UV-visible spectrophotometry
- Flame photometry
- Polarimetry
Correct Answer: UV-visible spectrophotometry
Q7. What characteristic physical property is commonly used to assess purity of isolated caffeine?
- Boiling point at atmospheric pressure
- Melting point (sharp range)
- Flash point
- Vapor pressure
Correct Answer: Melting point (sharp range)
Q8. Which chromatography technique is most often used in undergraduate labs to check purity of isolated caffeine?
- Gas chromatography with MS
- Thin layer chromatography (TLC)
- Size-exclusion chromatography
- Ion-exchange chromatography
Correct Answer: Thin layer chromatography (TLC)
Q9. In a liquid–liquid extraction of basified tea extract, which factor most increases caffeine partition into the organic layer?
- Lowering pH of aqueous phase
- Increasing polarity of organic solvent
- Using a denser organic solvent immiscible with water and favoring neutral caffeine solubility
- Adding salt to the organic layer
Correct Answer: Using a denser organic solvent immiscible with water and favoring neutral caffeine solubility
Q10. Which functional group signals would you expect in the IR spectrum of pure caffeine?
- Strong broad O-H peak near 3300 cm-1
- Carbonyl C=O stretches around 1700–1750 cm-1 and C–N bands
- Alkene C=C stretch as the main peak
- Sharp N–H stretch at 3400 cm-1
Correct Answer: Carbonyl C=O stretches around 1700–1750 cm-1 and C–N bands
Q11. What is an advantage of using Soxhlet extraction for isolating caffeine from tea dust?
- Requires no solvent
- Continuous hot solvent extraction increases recovery from solid matrix
- It is a dry distillation method
- It converts caffeine to a volatile derivative
Correct Answer: Continuous hot solvent extraction increases recovery from solid matrix
Q12. Which of these solvents is least suitable for extracting caffeine from aqueous basified solution?
- Chloroform
- Ethyl acetate
- Hexane
- Dichloromethane
Correct Answer: Hexane
Q13. Why is it important to dry the organic extract over anhydrous sodium sulfate before evaporation?
- To oxidize caffeine
- To remove dissolved water that can cause impurity during crystallization
- To increase solvent polarity
- To neutralize any acids present
Correct Answer: To remove dissolved water that can cause impurity during crystallization
Q14. Which recrystallization solvent choice is appropriate to purify crude caffeine?
- Solvent in which caffeine is highly soluble at room temperature and insoluble when hot
- Solvent in which caffeine is insoluble at all temperatures
- Solvent where caffeine has moderate solubility in hot solvent and poor solubility in cold solvent
- Any solvent miscible with water
Correct Answer: Solvent where caffeine has moderate solubility in hot solvent and poor solubility in cold solvent
Q15. Which of the following safety practices is essential during solvent extraction of caffeine?
- Work in a fume hood and avoid open flames due to flammable solvents
- Use solvent near a Bunsen burner to accelerate evaporation
- Store all organic waste in a sink
- Discard used sodium sulfate in regular trash without labeling
Correct Answer: Work in a fume hood and avoid open flames due to flammable solvents
Q16. During TLC analysis of tea extract on silica gel with a nonpolar mobile phase, caffeine will generally show:
- A very high Rf close to solvent front
- A moderate-to-low Rf due to polar interactions with silica
- No spot because caffeine is not chromophoric
- Splitting into multiple unrelated spots always
Correct Answer: A moderate-to-low Rf due to polar interactions with silica
Q17. Which statement about caffeine solubility is correct?
- Caffeine is insoluble in hot water but soluble in cold water
- Caffeine is freely soluble in nonpolar solvents like hexane
- Caffeine has appreciable solubility in hot water and in moderately polar organic solvents
- Caffeine reacts with water to form a salt
Correct Answer: Caffeine has appreciable solubility in hot water and in moderately polar organic solvents
Q18. Which reagent would you use to acidify an organic extract to convert free-base alkaloids to water-soluble salts?
- Sodium hydroxide solution
- Dilute hydrochloric acid
- Anhydrous sodium sulfate
- Liquid ammonia
Correct Answer: Dilute hydrochloric acid
Q19. What is the primary reason for performing multiple successive extractions rather than a single large-volume extraction?
- Multiple extractions with small volumes give better overall recovery due to partitioning principles
- Single large extraction is always more efficient
- Successive extractions reduce solvent purity
- It increases formation of emulsions deliberately
Correct Answer: Multiple extractions with small volumes give better overall recovery due to partitioning principles
Q20. Which calculation is essential to report the efficiency of caffeine isolation from tea dust?
- Percent transmittance of UV only
- Percent yield (recovery) of caffeine relative to starting material
- Total volume of solvent used without yield
- pH of the final aqueous wash only
Correct Answer: Percent yield (recovery) of caffeine relative to starting material
Q21. Which impurity is most likely to co-extract with caffeine from tea and may require additional purification?
- Cellulose fibers
- Polyphenolic compounds such as tannins
- Inorganic salts
- Metals like iron
Correct Answer: Polyphenolic compounds such as tannins
Q22. What is the typical UV λmax used for quantitative estimation of caffeine in aqueous solution?
- 210 nm
- 273 nm
- 340 nm
- 500 nm
Correct Answer: 273 nm
Q23. Which statement correctly explains partition coefficient (K) relevance in caffeine extraction?
- K is the ratio of concentration of caffeine in inert gas to solid phase
- A higher K (organic/aqueous) means caffeine preferentially partitions into organic solvent enhancing extraction
- K is irrelevant for liquid–liquid extraction
- K only applies to gas chromatography
Correct Answer: A higher K (organic/aqueous) means caffeine preferentially partitions into organic solvent enhancing extraction
Q24. In an extraction protocol, which step helps prevent emulsions when mixing organic and aqueous layers?
- Vigorous shaking for extended time
- Adding brine (saturated NaCl) and gentle mixing to break emulsions
- Using incompatible solvents to force mixing
- Heating to boiling to separate phases
Correct Answer: Adding brine (saturated NaCl) and gentle mixing to break emulsions
Q25. Which laboratory observation indicates formation of relatively pure caffeine crystals after recrystallization?
- Oily residue that does not crystallize
- Needle-like or crystalline solids with a sharp melting point close to literature value
- Colored syrupy mass with low melting point
- Complete loss of mass due to decomposition
Correct Answer: Needle-like or crystalline solids with a sharp melting point close to literature value
Q26. During isolation, why might a chemist perform a charcoal decolorization step before recrystallization?
- To remove kafirin proteins
- To adsorb colored impurities (pigments/tannins) that cause discoloration
- To catalyze conversion of caffeine to theobromine
- To increase solubility of caffeine
Correct Answer: To adsorb colored impurities (pigments/tannins) that cause discoloration
Q27. Which is an appropriate waste disposal practice for spent organic solvents from caffeine extraction?
- Pour them down the laboratory sink
- Collect in a labeled organic solvent waste container for hazardous waste disposal
- Evaporate to dryness in the open room
- Dispose in regular trash bins
Correct Answer: Collect in a labeled organic solvent waste container for hazardous waste disposal
Q28. Which reagent would you use to confirm presence of alkaloids like caffeine qualitatively in an extract?
- Mayer’s or Dragendorff’s reagent giving characteristic precipitate
- Benedict’s reagent for reducing sugars
- Biuret reagent for proteins
- Molisch’s test for carbohydrates
Correct Answer: Mayer’s or Dragendorff’s reagent giving characteristic precipitate
Q29. If isolated caffeine shows a melting point significantly lower than literature, what is the most likely explanation?
- The sample is ultra-pure
- Presence of impurities or solvent inclusion lowering the melting point
- Caffeine always melts at lower temperatures in labs
- Melting point apparatus was too cold
Correct Answer: Presence of impurities or solvent inclusion lowering the melting point
Q30. Which of the following best summarizes a standard laboratory workflow for isolating caffeine from tea dust?
- Direct distillation of tea dust to collect caffeine vapor
- Defatting, hot aqueous extraction, basification, liquid–liquid extraction into organic solvent, drying, solvent removal, recrystallization and analysis
- Grinding tea dust and analyzing directly without extraction
- Electrolytic separation of caffeine from tea dust
Correct Answer: Defatting, hot aqueous extraction, basification, liquid–liquid extraction into organic solvent, drying, solvent removal, recrystallization and analysis
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