Introduction: Tannins are important plant polyphenols encountered in pharmacognosy, affecting drug formulation, stability and bioactivity. Tests for tannins help B. Pharm students identify hydrolyzable and condensed tannins, understand qualitative reagents (ferric chloride, gelatin, lead acetate, vanillin-HCl, DMACA, acid‑butanol), interpret color changes and precipitates, and recognize limitations and false positives with other phenolics. Mastery of tannin tests enhances skills in phytochemical screening, sample preparation, protein‑precipitation mechanisms, astringency effects, and basic quantification methods. This concise, keyword-rich overview prepares you for laboratory identification and exam questions. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. Which reagent gives a blue‑black or green‑black color with tannins and is commonly used as a preliminary qualitative test?
- 5% Ferric chloride solution
- 10% Lead acetate solution
- Vanillin‑HCl reagent
- Gelatin solution with NaCl
Correct Answer: 5% Ferric chloride solution
Q2. The gelatin test for tannins detects tannins based on which principal reaction?
- Oxidation of phenolic groups producing color
- Precipitation of tannin–protein complexes
- Formation of colored anthocyanidins on heating
- Reduction of metallic salts to a colored oxide
Correct Answer: Precipitation of tannin–protein complexes
Q3. Which test is most specific for condensed tannins (proanthocyanidins), producing a red color on heating with acid and butanol?
- Lead acetate test
- Acid–butanol (Bate‑Smith) test
- Ferric chloride test
- Gelatin test
Correct Answer: Acid–butanol (Bate‑Smith) test
Q4. Vanillin‑HCl reagent is primarily used to detect which class of tannins or phenolics?
- Hydrolyzable tannins (gallotannins)
- Condensed tannins / flavan‑3‑ols
- Simple phenolic acids only
- Alkaloids
Correct Answer: Condensed tannins / flavan‑3‑ols
Q5. In the lead acetate test for tannins, what is the typical immediate observation?
- Blue‑black solution
- White precipitate of lead‑tannin complex
- Red coloration on gentle heating
- Frothing due to saponins
Correct Answer: White precipitate of lead‑tannin complex
Q6. Which reagent is considered more specific than vanillin for proanthocyanidins and gives a blue‑green color?
- 5% Ferric chloride
- DMACA (p‑dimethylaminocinnamaldehyde)
- Lead acetate
- Folin‑Denis reagent
Correct Answer: DMACA (p‑dimethylaminocinnamaldehyde)
Q7. Which statement best explains why ferric chloride test is not fully specific for tannins?
- It only reacts with proteins, not phenolics
- Many phenolic compounds (e.g., flavonoids, phenolic acids) also give color with FeCl3
- Ferric chloride dissolves tannins without color change
- It requires high temperature to react with tannins
Correct Answer: Many phenolic compounds (e.g., flavonoids, phenolic acids) also give color with FeCl3
Q8. Hydrolyzable tannins (e.g., gallotannins) typically yield which color with ferric chloride?
- Blue‑black
- Red
- Orange
- None — they do not react
Correct Answer: Blue‑black
Q9. Which qualitative test uses gelatin combined with sodium chloride to detect tannins by turbidity or precipitation?
- Folin‑Denis test
- Gelatin test
- Vanillin test
- Dragendorff’s test
Correct Answer: Gelatin test
Q10. The Folin‑Denis or Folin‑Ciocalteu assays are used to estimate:
- Total alkaloid content
- Total phenolic or tannin content colorimetrically
- Carbohydrate levels
Correct Answer: Total phenolic or tannin content colorimetrically
Q11. A sample gives a red color with vanillin‑HCl and a blue‑black with FeCl3. This pattern most likely indicates:
- Presence of alkaloids and saponins
- Presence of condensed tannins (proanthocyanidins) and general phenolics
- Absence of tannins
- Only hydrolyzable tannins are present
Correct Answer: Presence of condensed tannins (proanthocyanidins) and general phenolics
Q12. Which test gives a colored complex by reduction of phosphomolybdic‑phosphotungstic acid reagent and is used for total phenolics?
- Folin‑Ciocalteu (Folin‑Denis) assay
- Lead acetate test
- Gelatin precipitation
- Acid‑butanol test
Correct Answer: Folin‑Ciocalteu (Folin‑Denis) assay
Q13. Aqueous extraction is preferred for routine tannin screening because tannins are generally:
- Highly volatile
- Water‑soluble polyphenols
- Insouble in polar solvents
- Proteins rather than polyphenols
Correct Answer: Water‑soluble polyphenols
Q14. Which of the following correctly distinguishes hydrolyzable tannins from condensed tannins?
- Hydrolyzable tannins yield anthocyanidins on heating with acid; condensed do not
- Condensed tannins are polymers of flavan‑3‑ols and resist hydrolysis; hydrolyzable tannins yield gallic/ellagic acids on hydrolysis
- Both are identical chemically and indistinguishable by tests
- Hydrolyzable tannins are alkaloids while condensed are glycosides
Correct Answer: Condensed tannins are polymers of flavan‑3‑ols and resist hydrolysis; hydrolyzable tannins yield gallic/ellagic acids on hydrolysis
Q15. Which observation suggests a false positive when using gelatin test for tannins?
- Formation of a white precipitate due to added NaCl alone
- Immediate color change to red on heating
- Blue‑black color with FeCl3
- No turbidity
Correct Answer: Formation of a white precipitate due to added NaCl alone
Q16. The mechanism by which tannins exert astringency and precipitate proteins is primarily due to:
- Hydrophobic bonding only
- Formation of multiple hydrogen bonds and hydrophobic interactions with protein residues
- Cleavage of peptide bonds
- Oxidative cross‑linking mediated by metal ions only
Correct Answer: Formation of multiple hydrogen bonds and hydrophobic interactions with protein residues
Q17. Which of the following reagents produces a red anthocyanidin on heating with condensed tannins (confirmatory test)?
- HNO3 at room temperature
- Butanol‑HCl (acid‑butanol) reagent on heating
- 10% NaOH solution
- Lead acetate without heating
Correct Answer: Butanol‑HCl (acid‑butanol) reagent on heating
Q18. When testing plant extracts, which combination provides greater specificity for tannin identification?
- Only ferric chloride test
- Gelatin test plus vanillin/DMACA and acid‑butanol confirmation
- Only lead acetate test
- Only Folin‑Ciocalteu assay
Correct Answer: Gelatin test plus vanillin/DMACA and acid‑butanol confirmation
Q19. A herbal extract gives a positive DMACA test. Which compound class is most likely present?
- Alkaloids
- Proanthocyanidins (condensed tannins), catechins
- Simple sugars
- Terpenes
Correct Answer: Proanthocyanidins (condensed tannins), catechins
Q20. Which limitation applies when using lead acetate for tannin detection in a teaching lab?
- Lead acetate is non‑toxic and causes no disposal issues
- Lead salts are toxic and require careful handling and waste management
- Lead acetate gives a unique color not produced by other phenolics
- Lead acetate cannot precipitate tannins at any concentration
Correct Answer: Lead salts are toxic and require careful handling and waste management
Q21. A sample yields no precipitation with gelatin but reacts with FeCl3. This suggests:
- Presence of non‑tannin phenolics that give color with FeCl3 but do not precipitate proteins
- Strong presence of tannins that only react with gelatin
- Complete absence of phenolic compounds
- Sample is contaminated with proteins interfering with FeCl3
Correct Answer: Presence of non‑tannin phenolics that give color with FeCl3 but do not precipitate proteins
Q22. Which test can be used to differentiate between hydrolyzable and condensed tannins?
- Heating with acidified methanol (acid‑butanol) to yield red anthocyanidins for condensed tannins
- Thin layer chromatography only
- Flame test for potassium
- Solubility in hexane
Correct Answer: Heating with acidified methanol (acid‑butanol) to yield red anthocyanidins for condensed tannins
Q23. In quality control, why is it important to detect tannins in herbal formulations?
- Tannins can affect drug bioavailability, cause protein precipitation, and alter organoleptic properties
- Tannins always enhance solubility of drugs
- Tannins are required to activate all alkaloids
- Tannins prevent microbial growth in all cases
Correct Answer: Tannins can affect drug bioavailability, cause protein precipitation, and alter organoleptic properties
Q24. Which of the following colorimetric changes indicates a positive Folin‑Ciocalteu (total phenolic) assay?
- Development of blue color measured spectrophotometrically
- Immediate formation of a white precipitate
- Evolution of gas bubbles
- Solution turning clear and colorless
Correct Answer: Development of blue color measured spectrophotometrically
Q25. During a tannin test, formation of a darkening or black precipitate with potassium dichromate would most likely indicate:
- Presence of strong reducing sugars
- Oxidizable phenolic substances including tannins reacting with dichromate
- High lipid content
- Only proteins without phenolics
Correct Answer: Oxidizable phenolic substances including tannins reacting with dichromate
Q26. Which procedural step improves specificity when testing for tannins in crude extracts?
- Using concentrated sulfuric acid without controls
- Performing sequential tests (FeCl3, gelatin, vanillin/DMACA, acid‑butanol) and including positive and negative controls
- Testing only once with a single reagent
- Adding table salt to all reagents
Correct Answer: Performing sequential tests (FeCl3, gelatin, vanillin/DMACA, acid‑butanol) and including positive and negative controls
Q27. The presence of tannins can interfere with which analytical technique if not removed from plant extracts?
- Chromatography and protein assays due to precipitation and binding
- Infrared spectroscopy which is immune to tannins
- None — tannins never interfere
- Only flame photometry for sodium
Correct Answer: Chromatography and protein assays due to precipitation and binding
Q28. Which statement about DMACA reagent is correct?
- DMACA gives a red color with hydrolyzable tannins only
- DMACA reacts with flavan‑3‑ols (catechins) producing a blue‑green color, useful for condensed tannins
- DMACA is used to detect sugars
- DMACA is identical to ferric chloride in reactivity
Correct Answer: DMACA reacts with flavan‑3‑ols (catechins) producing a blue‑green color, useful for condensed tannins
Q29. If an extract gives a strong Folin‑Ciocalteu response but is negative with gelatin and vanillin tests, the likely conclusion is:
- The extract contains non‑tannin phenolics contributing to total phenolic value
- Extract is rich in condensed tannins exclusively
- There are only proteins present
- The extract is pure tannic acid
Correct Answer: The extract contains non‑tannin phenolics contributing to total phenolic value
Q30. For a confirmatory identification of hydrolyzable tannins, which hydrolysis product is typically detected?
- Gallic acid or ellagic acid after hydrolysis of gallotannins/ellagitannins
- Glucose only
- Alkaloid derivatives
- Fatty acids
Correct Answer: Gallic acid or ellagic acid after hydrolysis of gallotannins/ellagitannins
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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