Structure and uses of salicylic acid MCQs With Answer
Salicylic acid, an ortho-hydroxybenzoic acid widely studied in pharmaceutical chemistry, combines a phenolic hydroxyl and a carboxylic acid group, giving unique physicochemical and biological properties. B. Pharm students should master its molecular formula, pKa values, synthesis (including conversion to aspirin), analytical identification (IR, NMR, UV), formulation roles (keratolytic, antiseborrheic, anti-acne), concentrations for topical use, and safety/contraindications. These MCQs cover structure, mechanism, synthesis, formulation, stability and analysis to deepen understanding for exams and practical work. Now let’s test your knowledge with 50 MCQs on this topic.
Q1. What is the IUPAC name of salicylic acid?
- 2-Hydroxybenzoic acid
- 3-Hydroxybenzoic acid
- 4-Hydroxybenzoic acid
- 2-Methoxybenzoic acid
Correct Answer: 2-Hydroxybenzoic acid
Q2. What is the molecular formula of salicylic acid?
- C7H6O3
- C7H8O3
- C8H8O3
- C6H6O3
Correct Answer: C7H6O3
Q3. Which functional groups are present in salicylic acid?
- Phenolic hydroxyl and carboxylic acid
- Alcohol and ester
- Aldehyde and ketone
- Amide and ether
Correct Answer: Phenolic hydroxyl and carboxylic acid
Q4. What is the approximate molecular weight of salicylic acid?
- 138.12 g/mol
- 150.17 g/mol
- 122.12 g/mol
- 180.16 g/mol
Correct Answer: 138.12 g/mol
Q5. Which position is the hydroxyl group located relative to the carboxyl in salicylic acid?
- Ortho position (adjacent)
- Meta position
- Para position
- Separated by three carbons
Correct Answer: Ortho position (adjacent)
Q6. What is the approximate pKa of the carboxylic acid group in salicylic acid?
- ~3.0
- ~7.4
- ~10.5
- ~13.4
Correct Answer: ~3.0
Q7. Which pKa corresponds to the phenolic hydroxyl of salicylic acid?
- ~13.4
- ~3.0
- ~7.0
- ~5.5
Correct Answer: ~13.4
Q8. How does solubility of salicylic acid change with pH?
- Solubility increases at high pH due to ionization
- Solubility decreases at high pH
- Solubility is independent of pH
- Solubility peaks at pH 2 only
Correct Answer: Solubility increases at high pH due to ionization
Q9. Which reagent is commonly used to synthesize aspirin (acetylsalicylic acid) from salicylic acid?
- Acetic anhydride
- Hydrochloric acid
- Sodium hydroxide
- Hydrogen peroxide
Correct Answer: Acetic anhydride
Q10. Which bond is formed during conversion of salicylic acid to aspirin?
- Ester bond at the phenolic hydroxyl
- Ester bond at the carboxyl group
- Amide bond at the carboxyl
- Ether bond at the phenolic oxygen
Correct Answer: Ester bond at the phenolic hydroxyl
Q11. Which IR absorption is characteristic for the carboxyl C=O in salicylic acid?
- ~1700 cm-1
- ~2250 cm-1
- ~3000 cm-1
- ~1450 cm-1
Correct Answer: ~1700 cm-1
Q12. What UV-visible absorption is typical for salicylic acid due to aromatic conjugation?
- λmax around 296 nm
- λmax around 220 nm only
- λmax around 400 nm
- No UV absorption
Correct Answer: λmax around 296 nm
Q13. Which analytic technique can distinguish salicylic acid from acetylsalicylic acid by monitoring the acetyl signal?
- 1H NMR spectroscopy
- Melting point determination only
- Paper chromatography exclusively
- Colorimetric test only
Correct Answer: 1H NMR spectroscopy
Q14. What is the typical melting point of pure salicylic acid?
- ~159 °C
- ~98 °C
- ~220 °C
- ~75 °C
Correct Answer: ~159 °C
Q15. Which of the following is a primary pharmaceutical use of salicylic acid?
- Keratolytic agent in topical formulations
- Systemic antihypertensive
- Dermal anesthetic for surgery
- Parenteral anticoagulant
Correct Answer: Keratolytic agent in topical formulations
Q16. At which concentration range is salicylic acid typically used in acne cleansers?
- 0.5–2%
- 5–10%
- 15–20%
- 25–40%
Correct Answer: 0.5–2%
Q17. For wart and corn removal, which higher concentration range of salicylic acid is commonly used OTC?
- 10–40%
- 0.1–0.5%
- 2–5%
- 50–70%
Correct Answer: 10–40%
Q18. How does salicylic acid exert its keratolytic action?
- By solubilizing intercellular cement and promoting desquamation
- By inhibiting DNA replication in keratinocytes
- By acting as a local anesthetic
- By forming a protective polymer film
Correct Answer: By solubilizing intercellular cement and promoting desquamation
Q19. Which salt form increases aqueous solubility of salicylic acid for pharmaceutical use?
- Sodium salicylate
- Calcium salicylate only
- Magnesium salicylate only
- Potassium permanganate
Correct Answer: Sodium salicylate
Q20. Which property of salicylic acid makes it useful in anti-dandruff shampoos?
- Antiseborrheic and keratolytic effects
- Strong surfactant action
- Systemic antifungal activity
- High foaming capability
Correct Answer: Antiseborrheic and keratolytic effects
Q21. Which reaction transforms salicylic acid into methyl salicylate (oil of wintergreen)?
- Esterification of the carboxyl group with methanol
- Oxidation of the phenolic OH
- Nitration of the aromatic ring
- Hydrogenation of the aromatic ring
Correct Answer: Esterification of the carboxyl group with methanol
Q22. In synthesis of aspirin, what is the role of acid catalyst like sulfuric acid?
- To activate acetic anhydride and promote acetylation
- To oxidize salicylic acid
- To reduce the aromatic ring
- To hydrolyze acetate
Correct Answer: To activate acetic anhydride and promote acetylation
Q23. Which side effect is commonly associated with topical salicylic acid if overused?
- Skin irritation and peeling
- Systemic hypotension
- Renal failure
- Permanent pigmentation only
Correct Answer: Skin irritation and peeling
Q24. What is a major safety concern when applying high concentrations of salicylic acid over large areas?
- Systemic salicylate toxicity due to absorption
- Immediate anaphylaxis in all patients
- Formation of carcinogenic metabolites on skin
- Irreversible tanning of the skin
Correct Answer: Systemic salicylate toxicity due to absorption
Q25. Which formulation type is commonly used to deliver salicylic acid for acne?
- Gel or lotion at low percentage
- Intravenous solution
- Transdermal patch delivering systemic doses
- Ophthalmic drops
Correct Answer: Gel or lotion at low percentage
Q26. How is salicylic acid chemically classified among benzoic acid derivatives?
- Ortho-hydroxy derivative of benzoic acid
- Meta-nitro derivative of benzoic acid
- Para-alkyl derivative of benzoic acid
- Amide derivative of benzoic acid
Correct Answer: Ortho-hydroxy derivative of benzoic acid
Q27. Which of the following analytical tests is specific for phenolic OH in salicylic acid?
- Ferric chloride test producing purple color
- Bromine water decolorization only
- Tollens’ test silver mirror
- Biuret test for proteins
Correct Answer: Ferric chloride test producing purple color
Q28. Which of the following is an industrial application of salicylic acid beyond pharmaceuticals?
- Intermediate in dye and fragrance synthesis
- Primary fuel additive for petrol
- Main component in concrete hardeners
- Food emulsifier at high concentration
Correct Answer: Intermediate in dye and fragrance synthesis
Q29. Which microbial safety consideration applies to salicylic acid formulations?
- It is not a preservative; formulations require appropriate preservatives
- It is a broad-spectrum preservative eliminating need for others
- It is antiseptic at all pH values without preservatives
- It sterilizes products sterilized by autoclaving only
Correct Answer: It is not a preservative; formulations require appropriate preservatives
Q30. In TLC identification of salicylic acid, what effect does using a basic mobile phase have?
- Deprotonation increases Rf due to increased polarity of salt
- No effect on Rf value
- Causes salicylic acid to polymerize on the plate
- Makes the compound non-detectable by UV
Correct Answer: Deprotonation increases Rf due to increased polarity of salt
Q31. Which is the best storage condition for salicylic acid raw material?
- Cool, dry, protected from light
- Hot and humid environment
- Exposed to direct sunlight
- Submerged in water
Correct Answer: Cool, dry, protected from light
Q32. Which statement about salicylic acid metabolism is correct?
- Topical salicylic acid can be absorbed and metabolized to salicylate systemically
- Topical application is completely non-absorbed and inert systemically
- It is converted into aspirin in the skin
- It is metabolized to paracetamol in the liver
Correct Answer: Topical salicylic acid can be absorbed and metabolized to salicylate systemically
Q33. Which is a contraindication for using high-dose topical salicylic acid?
- Large-area application in infants and small children
- Use on limited, thickened calluses
- Applying to hyperkeratotic corns only
- Using as a component of medicated shampoo
Correct Answer: Large-area application in infants and small children
Q34. Which pH condition would most favor formation of sodium salicylate from salicylic acid?
- Alkaline pH above its pKa (~>7)
- Strongly acidic pH below 1
- Neutral pH only
- pH does not affect salt formation
Correct Answer: Alkaline pH above its pKa (~>7)
Q35. Which class of drugs is aspirin (derived from salicylic acid) primarily grouped under?
- Nonsteroidal anti-inflammatory drugs (NSAIDs)
- Beta-blockers
- ACE inhibitors
- Antifungals
Correct Answer: Nonsteroidal anti-inflammatory drugs (NSAIDs)
Q36. Which mechanism best describes aspirin’s analgesic effect compared to salicylic acid?
- Aspirin irreversibly acetylates COX enzymes; salicylic acid lacks strong irreversible acetylation
- Both irreversibly acetylate COX at equal potency
- Salicylic acid acetylates COX irreversibly, aspirin does not
- Neither affects COX; both act as local anesthetics
Correct Answer: Aspirin irreversibly acetylates COX enzymes; salicylic acid lacks strong irreversible acetylation
Q37. Which statement about the acidity of salicylic acid is correct?
- Intramolecular hydrogen bonding stabilizes the neutral form, slightly increasing acidity of carboxyl
- It is less acidic than benzoic acid due to the hydroxyl group always donating electrons
- It has two equally acidic protons both with pKa ~3
- Phenolic OH is more acidic than carboxyl group
Correct Answer: Intramolecular hydrogen bonding stabilizes the neutral form, slightly increasing acidity of carboxyl
Q38. Which is a common preservative concern when formulating salicylic acid shampoos?
- Compatibility at acidic pH to maintain salicylic acid solubility and preservative efficacy
- Preservatives are unnecessary due to salicylic acid’s high antimicrobial activity
- Only volatile preservatives can be used
- Preservatives must be highly alkaline
Correct Answer: Compatibility at acidic pH to maintain salicylic acid solubility and preservative efficacy
Q39. Which reagent can be used to selectively methylate the carboxyl group of salicylic acid to form methyl salicylate?
- Diazomethane
- Hydrochloric acid
- Sodium borohydride
- Chromic acid
Correct Answer: Diazomethane
Q40. In HPLC analysis, how does ionization state of salicylic acid affect retention on a reversed-phase column?
- Ionized form elutes earlier (reduced retention) than neutral form
- Ionized form retains longer than neutral form
- Ionization state has no effect on retention
- Ionized form cannot be detected by HPLC
Correct Answer: Ionized form elutes earlier (reduced retention) than neutral form
Q41. Which is the correct description of salicylic acid’s anti-inflammatory action when applied topically?
- Reduces inflammation via local modulation of inflammatory mediators and keratolysis
- Acts as a systemic steroid upon topical use
- Inhibits viral replication causing inflammation reduction
- Functions solely as a physical exfoliant without biochemical effects
Correct Answer: Reduces inflammation via local modulation of inflammatory mediators and keratolysis
Q42. Which is a typical preservative pH compatibility concern when combining salicylic acid with parabens?
- Parabens are more effective near neutral to mildly acidic pH; salicylic acid requires acidic conditions for solubility
- Parabens and salicylic acid react to form toxic compounds at pH 8
- Parabens are ineffective below pH 1 only
- Parabens always enhance salicylic acid stability at any pH
Correct Answer: Parabens are more effective near neutral to mildly acidic pH; salicylic acid requires acidic conditions for solubility
Q43. Which impurity test is important for salicylic acid raw material?
- Assay for ash and organic impurities by HPLC
- Test for heavy metals only by color change
- Water content irrelevant for solids
- No impurity tests required for pharmaceutical grade
Correct Answer: Assay for ash and organic impurities by HPLC
Q44. Which chemical transformation of salicylic acid increases its volatility and fragrance use?
- Esterification to methyl salicylate
- Nitration to nitrosalicylate
- Hydrogenation to cyclohexanol derivative
- Carboxyl reduction to alcohol only
Correct Answer: Esterification to methyl salicylate
Q45. Which chromatographic mobile phase condition would help separate salicylic acid from closely related acids?
- Buffer pH control to manipulate ionization state
- Using pure water only always
- Using saturated hydrocarbon solvent only
- Adding heavy metals to mobile phase
Correct Answer: Buffer pH control to manipulate ionization state
Q46. Which statement about patient counseling for topical salicylic acid is correct?
- Avoid applying to broken skin and extensive areas; follow concentration and duration instructions
- It is safe to apply on mucous membranes and eyes
- It can be ingested to treat fever safely
- No precautions are needed for pediatric use
Correct Answer: Avoid applying to broken skin and extensive areas; follow concentration and duration instructions
Q47. Which metal ion forms insoluble complexes with salicylate useful in qualitative tests?
- Iron(III) giving violet complexes with phenolic OH
- Sodium forming precipitates
- Lead forming colorless complexes only
- Calcium causing red precipitate
Correct Answer: Iron(III) giving violet complexes with phenolic OH
Q48. Which stability issue is most relevant for salicylic acid in formulations?
- Oxidation and interactions with strong bases leading to degradation
- Spontaneous polymerization at 25 °C in sealed containers
- Explosive decomposition in dilute aqueous solutions
- Complete insolubility at all pH values causing instability
Correct Answer: Oxidation and interactions with strong bases leading to degradation
Q49. Which controlled test is appropriate for assay of salicylic acid in a topical gel?
- HPLC or UV spectrophotometry with appropriate extraction
- Only organoleptic evaluation
- Measuring gel viscosity exclusively
- Mass spectrometry without extraction only
Correct Answer: HPLC or UV spectrophotometry with appropriate extraction
Q50. Which modification of salicylic acid reduces topical irritation while retaining keratolytic activity?
- Formulation as a buffered low-pH vehicle or using ester prodrugs
- Converting it into a basic salt for higher irritation
- Removing the phenolic OH chemically
- Heating it to polymerize before formulation
Correct Answer: Formulation as a buffered low-pH vehicle or using ester prodrugs
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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