Alkaloids are naturally occurring basic nitrogenous compounds with significant therapeutic and toxicological importance. Qualitative identification relies on classic spot and precipitation tests—Mayer’s, Dragendorff’s, Wagner’s, Hager’s and Bouchardat’s reagents—along with proper acid–base extraction and TLC visualization. B. Pharm students should master reagent composition, characteristic precipitate or color changes, procedural steps for extraction of alkaloid salts and free bases, limitations and confirmatory methods such as Kjeldahl nitrogen estimation. This focused practice covers reagent chemistry, interpretation of results, common interferences and practical laboratory workflow for alkaloid screening. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. Which reagent is known as Mayer’s reagent used in alkaloid detection?
- Potassium mercuric iodide (K2HgI4)
- Potassium bismuth iodide
- Saturated picric acid
- Iodine in alcohol
Correct Answer: Potassium mercuric iodide (K2HgI4)
Q2. Dragendorff’s reagent primarily contains which key metal ion?
- Bismuth
- Mercury
- Lead
- Silver
Correct Answer: Bismuth
Q3. Which test reagent gives a characteristic yellow crystalline precipitate with many alkaloids?
- Hager’s reagent (picric acid)
- Mayer’s reagent
- Wagner’s reagent
- Bouchardat’s reagent
Correct Answer: Hager’s reagent (picric acid)
Q4. Which reagent is prepared by dissolving iodine in potassium iodide and gives a brown or reddish-brown precipitate?
- Wagner’s reagent
- Mayer’s reagent
- Dragendorff’s reagent
- Hager’s reagent
Correct Answer: Wagner’s reagent
Q5. Which reagent is commonly used as a spray reagent to visualize alkaloids on TLC plates?
- Dragendorff’s reagent
- Hager’s reagent
- Mayer’s reagent
- Folin-Ciocalteu reagent
Correct Answer: Dragendorff’s reagent
Q6. What is the primary purpose of acidifying plant material during alkaloid extraction?
- To convert alkaloids into water-soluble salts
- To precipitate alkaloids as free bases
- To remove tannins selectively
- To oxidize alkaloids to quinones
Correct Answer: To convert alkaloids into water-soluble salts
Q7. After acid extraction of alkaloid salts, which step liberates the free alkaloid base for organic solvent extraction?
- Basification with alkali
- Addition of more acid
- Adding saturated salt solution
Correct Answer: Basification with alkali
Q8. Which test reagent contains mercury and may raise safety concerns in the laboratory?
- Mayer’s reagent
- Dragendorff’s reagent
- Hager’s reagent
- Bouchardat’s reagent
Correct Answer: Mayer’s reagent
Q9. Bouchardat’s reagent is best described as:
- Iodine dissolved in alcohol producing a brown precipitate
- Potassium mercuric iodide producing a cream precipitate
- Potassium bismuth iodide producing an orange-red precipitate
- Saturated picric acid producing yellow crystals
Correct Answer: Iodine dissolved in alcohol producing a brown precipitate
Q10. Which reagent typically gives a cream-colored precipitate with many alkaloids?
- Mayer’s reagent
- Wagner’s reagent
- Dragendorff’s reagent
- Hager’s reagent
Correct Answer: Mayer’s reagent
Q11. Which classical method is used for quantitative estimation of nitrogen in alkaloid samples?
- Kjeldahl method
- Biuret test
- Lowry method
- Bradford assay
Correct Answer: Kjeldahl method
Q12. Which property of alkaloids allows their separation by acid–base extraction?
- Their basic nitrogen that forms salts with acids
- Their hydrophobicity due to long alkyl chains
- Their susceptibility to oxidation
- Their polymeric nature
Correct Answer: Their basic nitrogen that forms salts with acids
Q13. A plant extract gives an orange-red precipitate with Dragendorff’s reagent on TLC. This indicates:
- Presence of alkaloids or alkaloid-like compounds
- Absence of nitrogenous compounds
- Presence of carbohydrates only
- Presence of phenolic acids exclusively
Correct Answer: Presence of alkaloids or alkaloid-like compounds
Q14. Which of the following is a limitation of simple spot tests for alkaloids?
- They can give false positives with tannins or other interfering substances
- They provide precise molecular structures directly
- They quantify exact alkaloid concentration with high accuracy
- They detect inorganic metals only
Correct Answer: They can give false positives with tannins or other interfering substances
Q15. Which reagent is most likely to produce an orange to brown stain on TLC for alkaloids and is widely used for sensitivity?
- Dragendorff’s reagent
- Hager’s reagent
- Mayer’s reagent
- Ferric chloride reagent
Correct Answer: Dragendorff’s reagent
Q16. What does a positive Wagner’s test indicate in a qualitative alkaloid exam?
- Formation of a brown or reddish-brown precipitate indicating alkaloids
- Blue coloration indicating tannins
- No reaction; Wagner’s reagent is specific for sugars
- Green color change indicating flavonoids
Correct Answer: Formation of a brown or reddish-brown precipitate indicating alkaloids
Q17. Which of the following reagents is based on picric acid and often gives a yellow crystalline precipitate with alkaloids?
- Hager’s reagent
- Mayer’s reagent
- Dragendorff’s reagent
- Wagner’s reagent
Correct Answer: Hager’s reagent
Q18. Why is basification often followed by extraction into an organic solvent during alkaloid isolation?
- To convert alkaloid salts into free bases that are soluble in organic solvents
- To decompose alkaloids into amino acids
- To remove metal ions bound to alkaloids
- To oxidize alkaloids to quinones
Correct Answer: To convert alkaloid salts into free bases that are soluble in organic solvents
Q19. Which test reagent’s reaction is most likely to be affected by the presence of excess iodide or oxidizing agents?
- Wagner’s reagent (iodine + KI)
- Mayer’s reagent
- Hager’s reagent
- Tannic acid test
Correct Answer: Wagner’s reagent (iodine + KI)
Q20. For preliminary screening of alkaloids in a crude extract, which combination of steps is most appropriate?
- Acidify extract → filter → basify → extract into organic solvent → apply spot tests
- Directly add Wagner’s reagent to crude powder without extraction
- Neutralize with buffer → add phenol reagent → heat
- Oxidize with permanganate → test with Folin reagent
Correct Answer: Acidify extract → filter → basify → extract into organic solvent → apply spot tests
Q21. Which statement about Dragendorff’s reagent is correct?
- It forms an orange-red or reddish-brown precipitate with many alkaloids and is highly sensitive
- It is a solution of picric acid and gives yellow crystals
- It contains mercury and gives a cream precipitate
- It is used primarily for carbohydrate detection
Correct Answer: It forms an orange-red or reddish-brown precipitate with many alkaloids and is highly sensitive
Q22. Which analytical technique is commonly used to confirm alkaloid identity after positive spot tests?
- Chromatography (TLC/HPLC) and spectroscopic methods (MS, NMR)
- Colorimetry with Folin reagent only
- Gravimetric sulfur estimation
- Polarimetry exclusively
Correct Answer: Chromatography (TLC/HPLC) and spectroscopic methods (MS, NMR)
Q23. If a sample gives a positive response with both Mayer’s and Hager’s reagents, this suggests:
- Presence of alkaloids that form precipitates with mercuric iodide and picrate ions
- Exclusive presence of proteins
- That the sample contains no basic compounds
- Presence of only carbohydrates
Correct Answer: Presence of alkaloids that form precipitates with mercuric iodide and picrate ions
Q24. Which reagent is least likely to be used when environmental or mercury-free alternatives are required?
- Mayer’s reagent
- Dragendorff’s reagent
- Hager’s reagent
- Bouchardat’s reagent
Correct Answer: Mayer’s reagent
Q25. Which feature distinguishes true alkaloids from related nitrogenous substances for qualitative testing?
- Presence of nitrogen in a heterocyclic ring derived from amino acids
- Being non-basic and water-insoluble salts
- Always lacking pharmacological activity
- Being polysaccharide in nature
Correct Answer: Presence of nitrogen in a heterocyclic ring derived from amino acids
Q26. When using Dragendorff’s reagent on a TLC plate, what is the typical visual outcome for alkaloids?
- Colored spots (orange/red/brown) at positions corresponding to alkaloids
- Complete dissolution of the silica gel
- Formation of blue fluorescent bands only under UV
- No visible change in any case
Correct Answer: Colored spots (orange/red/brown) at positions corresponding to alkaloids
Q27. Which of the following is a correct safety consideration when performing alkaloid spot tests?
- Handle potassium mercuric iodide and picric acid with care due to toxicity and explosive/hazard risk
- All reagents are harmless and require no PPE
- Only flammability is a concern; toxicity is negligible
- Reagents can be disposed of down the sink without neutralization
Correct Answer: Handle potassium mercuric iodide and picric acid with care due to toxicity and explosive/hazard risk
Q28. Which reagent would most reliably detect tertiary alkaloids in a dilute solution by precipitation?
- Dragendorff’s reagent
- Molisch reagent
- Benedict’s reagent
- Fehling’s solution
Correct Answer: Dragendorff’s reagent
Q29. During qualitative analysis, which interfering plant constituents commonly complicate alkaloid tests by forming precipitates?
- Tannins and phenolic compounds
- Inorganic chlorides exclusively
- Sugars that form colored complexes only
- Simple alkanes
Correct Answer: Tannins and phenolic compounds
Q30. In a lab practical, you obtain no precipitate with Mayer’s but a strong orange spot with Dragendorff’s on TLC. The most reasonable interpretation is:
- Alkaloids are present but may not precipitate with Mayer’s; Dragendorff’s is more sensitive
- No alkaloids are present; both tests are unreliable
- Alkaloids are present only as proteins
- The sample contains only carbohydrates
Correct Answer: Alkaloids are present but may not precipitate with Mayer’s; Dragendorff’s is more sensitive
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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