Structure and uses of salicylic acid MCQs With Answer

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

G S Sachin

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.

Mail- Sachin@pharmacyfreak.com