Determination of ester value of cosmetics MCQs With Answer

Introduction: Determination of the ester value is a key quality control test in cosmetic analysis, assessing the amount of esterified fatty acids (emollients and synthetic esters) present in creams, lotions and oils. This blog presents targeted MCQs to help M.Pharm students understand the principles, titrimetric procedure, reagents, calculations and practical pitfalls associated with ester value determination. Questions cover saponification and back-titration concepts, blank corrections, calculation examples in mg KOH/g, sample preparation, solvent and indicator selection, and interpretation of results for formulation stability and authenticity. These practice items reinforce the analytical reasoning and calculation skills required for laboratory and regulatory work in herbal and cosmetic analysis.

Q1. What is the definition of “ester value” in cosmetic analysis?

• Amount of free acid present in a sample expressed as mg KOH/g
• Mass of ester compounds in mg per gram of sample
• Amount of KOH (mg) required to saponify the ester groups in 1 g of sample
• Volume of alcoholic solvent required to dissolve 1 g of sample

Correct Answer: Amount of KOH (mg) required to saponify the ester groups in 1 g of sample

Q2. How is ester value most commonly obtained from related titrimetric parameters?

• Ester value = Acid value + Neutralization number
• Ester value = Saponification value – Acid value
• Ester value = Acid value – Saponification value
• Ester value = Saponification value × Acid value

Correct Answer: Ester value = Saponification value – Acid value

Q3. Which reagent is typically used to effect saponification of esters when determining ester value?

• Concentrated sulfuric acid
• Ethanolic potassium hydroxide (KOH)
• Sodium chloride solution
• Potassium permanganate

Correct Answer: Ethanolic potassium hydroxide (KOH)

Q4. Which indicator is most commonly used to detect the end point in the back titration of saponified cosmetic samples?

• Methyl orange
• Bromothymol blue
• Phenolphthalein
• Neutral red

Correct Answer: Phenolphthalein

Q5. Why is heating applied during the saponification step of ester value determination?

• To evaporate the solvent completely
• To ensure complete hydrolysis of ester bonds to alcohols and salts
• To precipitate insoluble impurities
• To convert free acids into esters

Correct Answer: To ensure complete hydrolysis of ester bonds to alcohols and salts

Q6. In what units is the ester value usually reported?

• mg HCl per g sample
• mg KOH per g sample
• mL NaOH per 100 g sample
• % w/w of esters

Correct Answer: mg KOH per g sample

Q7. What is the primary purpose of performing a blank determination in the ester value method?

• To measure the color of the reagent
• To correct for reagent consumption not due to sample esters (reagent impurities and solvent reactions)
• To standardize the balance used for weighing
• To determine the molecular weight of esters

Correct Answer: To correct for reagent consumption not due to sample esters (reagent impurities and solvent reactions)

Q8. Which of the following sample characteristics can interfere with an accurate ester value determination in cosmetics?

• Presence of non-saponifiable waxes only
• High content of volatile fragrance oils only
• Presence of free fatty acids and soaps that consume alkali
• Low viscosity of the sample

Correct Answer: Presence of free fatty acids and soaps that consume alkali

Q9. A cosmetic oil (2.000 g) is saponified and back-titrated. Blank titration required 25.00 mL of 0.5 N acid, sample required 18.50 mL of 0.5 N acid. A separate acid value determination gave 4.00 mg KOH/g. Using the formula Saponification value = (Vb – Vs) × N × 56.1 / W, what is the ester value (mg KOH/g)?

• 46.00 mg KOH/g
• 87.16 mg KOH/g
• 178.32 mg KOH/g
• 200.00 mg KOH/g

Correct Answer: 87.16 mg KOH/g

Q10. Which solvent is commonly used to dissolve cosmetic oil samples for the saponification step?

• Water
• Hexane
• Ethanol (alcohol)
• Acetone

Correct Answer: Ethanol (alcohol)

Q11. What acid is most often used for the back titration of excess alkali in the ester value procedure?

• Nitric acid
• Hydrochloric acid
• Acetic acid
• Sulfuric acid

Correct Answer: Hydrochloric acid

Q12. A high saponification value in a cosmetic lipid indicates which of the following about its composition?

• High proportion of long-chain fatty acids
• High proportion of low molecular weight (short-chain) esters or fatty acids
• High iodine value
• High content of non-saponifiable matter

Correct Answer: High proportion of low molecular weight (short-chain) esters or fatty acids

Q13. Which statement correctly contrasts acid value and ester value?

• Acid value measures bound esters; ester value measures free acids
• Acid value measures free acids; ester value measures esterified (saponifiable) material
• Both measure the same parameter but use different indicators
• Acid value is expressed in % w/w whereas ester value is a pH value

Correct Answer: Acid value measures free acids; ester value measures esterified (saponifiable) material

Q14. If a cosmetic sample has a saponification value of 200 mg KOH/g and an acid value of 10 mg KOH/g, what is the ester value?

• 10 mg KOH/g
• 210 mg KOH/g
• 190 mg KOH/g
• 2000 mg KOH/g

Correct Answer: 190 mg KOH/g

Q15. Which pharmacopeial sources commonly provide official procedures for ester or saponification determinations in cosmetic and lipid materials?

• Only the Merck Index
• Official pharmacopeias such as IP, USP and BP
• Textbooks only, not pharmacopeias
• International Organization for Standardization (ISO) exclusively

Correct Answer: Official pharmacopeias such as IP, USP and BP

Q16. What is the observable color change indicating the phenolphthalein end point in an alcoholic KOH titration?

• Pink to colorless
• Yellow to blue
• Colorless to persistent pink
• Blue to green

Correct Answer: Colorless to persistent pink

Q17. If the blank titration volume is lower than the sample titration volume (Vb < Vs), what is the most likely interpretation?

• The sample contains no esterifiable material
• There is an experimental error, incomplete saponification or excessive sample acidity causing more acid to be needed
• The ester value is simply negative and acceptable
• The indicator was omitted

Correct Answer: There is an experimental error, incomplete saponification or excessive sample acidity causing more acid to be needed

Q18. Which of the following esters are typical cosmetic emollients whose content may be evaluated indirectly via ester/saponification testing?

• Cetyl palmitate and isopropyl myristate
• Sodium chloride and potassium chloride
• Glycerol and ethylene glycol
• Citric acid and ascorbic acid

Correct Answer: Cetyl palmitate and isopropyl myristate

Q19. Which laboratory safety and disposal precaution is important when performing ester value determinations?

• Neutralize acidic and basic waste before disposal and avoid inhalation of volatile solvents
• Dispose of all reagents directly down the sink without neutralization
• Store concentrated acids near open flames for better reaction
• No special precautions are required for alcoholic KOH solutions

Correct Answer: Neutralize acidic and basic waste before disposal and avoid inhalation of volatile solvents

Q20. Which analytical factor directly affects the calculated ester value (mg KOH/g)?

• Color of the sample only
• Exact weight of sample used in the analysis
• Brand of indicator used, irrespective of volume
• Time of day when the analysis is performed

Correct Answer: Exact weight of sample used in the analysis

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