Qualitative tests for phenols MCQs With Answer

Introduction: Qualitative tests for phenols MCQs With Answer are essential for B.Pharm students studying analytical and organic pharmaceutical chemistry. These tests—such as the Ferric chloride test, bromine water reaction, sodium hydroxide solubility, and acetylation—help identify phenolic functional groups, distinguish phenols from alcohols and carboxylic acids, and detect substitution patterns (ortho/para activation). Mastery of reagent behavior, observed color changes, and reaction products enhances practical lab diagnostics and drug impurity analysis. This concise, keyword-rich guide focuses on common qualitative assays, mechanisms, and interpretation of results tailored for B.Pharm exam preparation. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which qualitative reagent gives a characteristic violet, blue or green color with phenols due to complex formation?

• Ferric chloride solution (FeCl3)
• Benedict’s reagent
• Tollens’ reagent
• Lucas reagent

Correct Answer: Ferric chloride solution (FeCl3)

Q2. Phenol reacts with bromine water to give which observable result?

• No change
• Decolorization with formation of a white precipitate
• Formation of a silver mirror
• Effervescence of CO2

Correct Answer: Decolorization with formation of a white precipitate

Q3. Which test can distinguish phenols from carboxylic acids using simple solubility differences?

• Solubility in dilute sodium hydroxide vs sodium bicarbonate
• Reaction with Tollens’ reagent
• Lucas test
• Bromination in CCl4

Correct Answer: Solubility in dilute sodium hydroxide vs sodium bicarbonate

Q4. Phenol forms a soluble salt with which base used as a qualitative test?

• Dilute sodium hydroxide
• Silver nitrate
• Ammonium chloride
• Lead(II) acetate

Correct Answer: Dilute sodium hydroxide

Q5. Which reagent selectively gives a precipitate of 2,4,6-tribromophenol with phenol?

• Bromine water
• Ferric chloride
• Hinsberg reagent
• Potassium permanganate

Correct Answer: Bromine water

Q6. Acetylation of a phenol with acetic anhydride is used as a qualitative test because:

• Phenol forms an ester (phenyl acetate) that can be identified
• It produces a silver mirror
• Phenol produces nitrogen gas
• It forms a coloured complex with iron

Correct Answer: Phenol forms an ester (phenyl acetate) that can be identified

Q7. Which of the following reagents will NOT give a positive test for phenol?

• Tollens’ reagent
• Ferric chloride solution
• Bromine water
• Acetic anhydride (with pyridine)

Correct Answer: Tollens’ reagent

Q8. The ferric chloride test for phenols is sensitive to what change in the phenolic molecule?

• Formation of phenoxide ion and complexation with Fe3+
• Oxidation to carboxylic acid
• Cleavage of the aromatic ring
• Nitration of the ring

Correct Answer: Formation of phenoxide ion and complexation with Fe3+

Q9. Which phenolic derivative gives a negative result with ferric chloride due to lack of free OH?

• Phenyl acetate (acetylated phenol)
• Unsubstituted phenol
• p-Cresol
• Resorcinol

Correct Answer: Phenyl acetate (acetylated phenol)

Q10. Which test can be used to differentiate phenol from a primary alcohol?

• Solubility in sodium hydroxide
• Lucas test
• Tollens’ test
• Schiff’s test

Correct Answer: Solubility in sodium hydroxide

Q11. Which product is commonly formed when phenol undergoes bromination in aqueous medium?

• 2,4,6-tribromophenol
• Phenyl bromide (Ar-Br)
• Benzyl bromide
• p-Bromobenzaldehyde

Correct Answer: 2,4,6-tribromophenol

Q12. A phenol gives a red or purple color with FeCl3. Which property of the phenol most influences the exact color?

• Type and position of ring substituents
• Boiling point of the phenol
• Melting point of the phenol
• Solubility in hexane

Correct Answer: Type and position of ring substituents

Q13. Which reagent produces a colored azo dye when phenol participates in coupling reactions?

• Diazonium salt (from an aromatic amine)
• Benedict’s reagent
• Lucas reagent
• Tollen’s reagent

Correct Answer: Diazonium salt (from an aromatic amine)

Q14. In the sodium hydroxide test, why do phenols dissolve while most alcohols do not?

• Phenols are acidic enough to form phenoxide ions with NaOH
• Alcohols form complexes with NaOH
• Phenols evaporate on contact with NaOH
• Alcohols polymerize in NaOH

Correct Answer: Phenols are acidic enough to form phenoxide ions with NaOH

Q15. Which of the following is a limitation of the ferric chloride test for phenols?

• Enols and some aromatic amines may give false positives
• It requires heating at 250°C
• It only detects aliphatic alcohols
• It destroys the aromatic ring

Correct Answer: Enols and some aromatic amines may give false positives

Q16. Which observation indicates a positive acetylation test for phenol?

• Formation of an ester with different solubility or melting point
• Immediate evolution of gas
• Formation of a metallic mirror
• Production of a green precipitate

Correct Answer: Formation of an ester with different solubility or melting point

Q17. Which reagent is commonly used to detect phenols by generating a colored complex through oxidation?

• Potassium permanganate (KMnO4)
• Sodium bicarbonate
• Brady’s reagent
• Lucas reagent

Correct Answer: Potassium permanganate (KMnO4)

Q18. Which of these phenols is most reactive toward electrophilic substitution and gives the fastest bromination in water?

• Phenol (unsubstituted)
• Nitrophenol (strongly deactivating)
• p-Chlorophenol
• p-Nitrophenol

Correct Answer: Phenol (unsubstituted)

Q19. Which qualitative test can detect phenols in presence of tertiary alcohols?

• Solubility in dilute NaOH (phenol dissolves, tertiary alcohol does not)
• Lucas test (tertiary alcohols react faster)
• Tollens’ reagent (detects aldehydes only)
• Chromic acid (tertiary alcohols oxidize easily)

Correct Answer: Solubility in dilute NaOH (phenol dissolves, tertiary alcohol does not)

Q20. Which statement about phenol’s reaction with sodium bicarbonate (NaHCO3) is correct?

• Most phenols do not react with NaHCO3, distinguishing them from carboxylic acids
• Phenols always effervesce vigorously with NaHCO3
• Phenols form insoluble salts with NaHCO3
• NaHCO3 converts phenols to aldehydes

Correct Answer: Most phenols do not react with NaHCO3, distinguishing them from carboxylic acids

Q21. Which reagent is used to detect free phenolic OH by formation of a colored complex with aluminium?

• Aluminium chloride (AlCl3) producing UV shifts and color in UV-visible
• Lucas reagent
• Benedict’s reagent
• Br2 in CCl4

Correct Answer: Aluminium chloride (AlCl3) producing UV shifts and color in UV-visible

Q22. Which qualitative test is useful to identify phenolic antioxidants in pharmaceutical formulations by reacting with bromine?

• Bromine water test leading to decolorization and precipitation
• Tollens’ test creating mirror
• Ninhydrin test for amines
• Benedict’s test for reducing sugars

Correct Answer: Bromine water test leading to decolorization and precipitation

Q23. Which reagent will distinguish phenol from anisole (methoxybenzene)?

• Dilute NaOH (phenol forms phenoxide; anisole does not)
• Bromine water (both react identically)
• Tollens’ reagent (both give silver mirror)
• Lucas reagent (both react quickly)

Correct Answer: Dilute NaOH (phenol forms phenoxide; anisole does not)

Q24. What color change is typically seen when phenol reacts with ferric chloride in dilute aqueous solution?

• Violet, blue or green coloration
• Bright yellow precipitation
• Silver mirror formation
• No visible change

Correct Answer: Violet, blue or green coloration

Q25. Which derivative of phenol will give a positive ferric chloride test even if the OH is not free?

• Phenols with adjacent electron-donating substituents that form enolic structures
• Fully methylated phenyl acetate
• Etherified phenols like anisole
• Carboxylic acids

Correct Answer: Phenols with adjacent electron-donating substituents that form enolic structures

Q26. What is the main chemical basis for bromine water decolorization by phenols?

• Electrophilic aromatic substitution leading to bromination and loss of bromine color
• Formation of a silver complex
• Acid-base neutralization producing CO2
• Complexation with Fe3+

Correct Answer: Electrophilic aromatic substitution leading to bromination and loss of bromine color

Q27. Which reagent is useful to detect phenols through oxidative coupling giving quinone-type products?

• Potassium permanganate (KMnO4)
• Sodium chloride
• Lucas reagent
• Tollens’ reagent

Correct Answer: Potassium permanganate (KMnO4)

Q28. In lab identification, why is acetylation followed by re-testing with FeCl3 useful for phenols?

• Acetylation blocks OH; loss of FeCl3 color confirms OH was responsible
• It makes phenol volatile
• It forms a silver mirror
• It causes immediate combustion

Correct Answer: Acetylation blocks OH; loss of FeCl3 color confirms OH was responsible

Q29. Which of the following gives a positive bromine test but a negative FeCl3 test?

• An activated aromatic hydrocarbon lacking free OH (e.g., activated aniline under some conditions)
• Unsubstituted phenol
• p-Nitrophenol
• Salicylic acid

Correct Answer: An activated aromatic hydrocarbon lacking free OH (e.g., activated aniline under some conditions)

Q30. Which compound will NOT dissolve in dilute NaOH: phenol, ethanol, acetic acid, or sodium phenoxide?

• Ethanol
• Phenol
• Acetic acid
• Sodium phenoxide

Correct Answer: Ethanol

Q31. For forensic identification of phenolic impurities in drugs, which combination of tests is most informative?

• FeCl3 test, NaOH solubility, and bromine test
• Lucas test, Benedict’s, and Tollens’ reagent
• Flame test, ceric nitrate, and ninhydrin
• Saponification, Iodoform, and Molisch test

Correct Answer: FeCl3 test, NaOH solubility, and bromine test

Q32. Which structural feature increases a phenol’s acidity and thus the ease of forming phenoxide for qualitative tests?

• Electron-withdrawing substituents (e.g., nitro) on the aromatic ring
• Electron-donating substituents (e.g., methoxy)
• Long alkyl chain on oxygen
• Allylic substitution on ring

Correct Answer: Electron-withdrawing substituents (e.g., nitro) on the aromatic ring

Q33. Which qualitative test is most suitable to confirm presence of ortho- or para- di-substituted phenols?

• Bromination (pattern and number of bromination sites) and spectroscopy
• Tollens’ test alone
• Ninhydrin test
• Benedict’s reagent

Correct Answer: Bromination (pattern and number of bromination sites) and spectroscopy

Q34. Which reagent is commonly used to acetylate phenols in a qualitative lab test?

• Acetic anhydride (often with pyridine or base)
• Concentrated HCl
• Br2 in CCl4
• Silver nitrate

Correct Answer: Acetic anhydride (often with pyridine or base)

Q35. A phenol sample gives a blue coloration with FeCl3 and insoluble residue after bromination. What does this indicate?

• Presence of a phenolic OH that is highly activated toward bromination (likely 2,4,6-substitution)
• Absence of any aromatic ring
• Sample is a carboxylic acid
• Compound is a tertiary alcohol

Correct Answer: Presence of a phenolic OH that is highly activated toward bromination (likely 2,4,6-substitution)

Q36. Which aromatic compound gives a strong FeCl3 color but is NOT a phenol?

• Some enols or beta-diketones that form chelates with Fe3+
• Benzene
• Toluene
• n-Hexane

Correct Answer: Some enols or beta-diketones that form chelates with Fe3+

Q37. Which qualitative change suggests successful conversion of phenol to its acetate?

• Loss of FeCl3 color and a new ester melting point or IR carbonyl band
• Formation of CO2 on acid addition
• Appearance of a silver mirror
• Immediate color change with KMnO4 to purple

Correct Answer: Loss of FeCl3 color and a new ester melting point or IR carbonyl band

Q38. Which of the following will react with bromine water but NOT give a ferric chloride color?

• Activated aromatic hydrocarbon lacking phenolic OH (e.g., an activated polyalkylbenzene)
• Phenol
• Resorcinol
• Hydroquinone

Correct Answer: Activated aromatic hydrocarbon lacking phenolic OH (e.g., an activated polyalkylbenzene)

Q39. In thin-layer qualitative tests, spotting phenol and spraying with FeCl3 gives coloration. What analytical follow-up confirms identity?

• IR spectroscopy showing O–H and aromatic bands and disappearance after acetylation
• Flame test for color
• Benedict’s test
• Specific gravity measurement only

Correct Answer: IR spectroscopy showing O–H and aromatic bands and disappearance after acetylation

Q40. Which observation rules out phenol as the functional group in an unknown sample?

• No reaction with FeCl3 and no solubility in NaOH
• Formation of precipitate with Pb(NO3)2
• Positive acetylation result

Correct Answer: No reaction with FeCl3 and no solubility in NaOH

Q41. Which phenolic isomer is most likely to give different staining or color intensity in FeCl3 test due to hydrogen bonding patterns?

• Ortho-substituted phenols (e.g., salicyl alcohol derivatives)
• Unsubstituted benzene
• Aliphatic alcohols
• Nitrobenzene

Correct Answer: Ortho-substituted phenols (e.g., salicyl alcohol derivatives)

Q42. Why might p-nitrophenol show a different color in FeCl3 test than phenol?

• Electron-withdrawing nitro group alters phenoxide complex electronic structure
• Presence of nitro group prevents solubility in water
• It forms a silver mirror
• p-Nitrophenol is not aromatic

Correct Answer: Electron-withdrawing nitro group alters phenoxide complex electronic structure

Q43. Which reagent can be used to demonstrate that the phenolic OH is acidic by liberating CO2 from carbonate?

• Actually, most phenols do NOT liberate CO2 with NaHCO3, unlike carboxylic acids
• Sodium bicarbonate always liberates CO2 with phenols
• Tollens’ reagent liberates CO2
• Bromine water liberates CO2

Correct Answer: Actually, most phenols do NOT liberate CO2 with NaHCO3, unlike carboxylic acids

Q44. Which classical qualitative test for phenols involves formation of coloured quinone-like products upon oxidation?

• Oxidation with ferric chloride or KMnO4 producing colored products
• Lucas reagent test
• Molisch test
• Biuret test

Correct Answer: Oxidation with ferric chloride or KMnO4 producing colored products

Q45. Which statement is true about the behavior of polyhydric phenols (e.g., resorcinol, hydroquinone) in qualitative tests?

• They often give stronger or different colors with FeCl3 and faster bromination than monophenols
• They never react with FeCl3
• They are insoluble in NaOH
• They cannot be acetylated

Correct Answer: They often give stronger or different colors with FeCl3 and faster bromination than monophenols

Q46. What is the practical lab advantage of performing both NaOH solubility and FeCl3 tests on an unknown sample?

• Combining acid-base solubility and complexation reduces false positives and confirms phenolic OH
• They both produce identical results always
• Both tests destroy the sample completely so no further tests possible
• They are useful only for aliphatic alcohols

Correct Answer: Combining acid-base solubility and complexation reduces false positives and confirms phenolic OH

Q47. A pharmaceutical impurity gives immediate white precipitate on addition of bromine water to its aqueous solution. This suggests presence of:

• A highly activated phenolic compound
• An aliphatic alcohol
• A carboxylic acid
• An alkane

Correct Answer: A highly activated phenolic compound

Q48. Which modern instrumental follow-up best complements classical qualitative phenol tests in B.Pharm labs?

• Infrared spectroscopy (IR) to detect O–H and C–O or ester bands
• Flame photometry for sodium content
• Polarimetry only
• Moisture balance

Correct Answer: Infrared spectroscopy (IR) to detect O–H and C–O or ester bands

Q49. During qualitative testing, heating a phenolic sample with acetic anhydride produces a characteristic smell and solid product. What does this indicate?

• Successful acetylation forming phenyl acetate (ester)
• Complete oxidation to carbon dioxide
• Formation of an amide
• Polymerization to a resin

Correct Answer: Successful acetylation forming phenyl acetate (ester)

Q50. Which sequence of observations most strongly confirms a phenolic functional group in an unknown organic solid?

• Soluble in NaOH, gives violet/green color with FeCl3, decolorizes bromine water forming precipitate
• Insoluble in NaOH, gives silver mirror, forms carboxylate with NaHCO3
• Positive Lucas test, no change with FeCl3, forms ketone on oxidation
• No reaction with any reagent

Correct Answer: Soluble in NaOH, gives violet/green color with FeCl3, decolorizes bromine water forming precipitate

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