Determination of acid value of cosmetic products MCQs With Answer

Determination of acid value of cosmetic products MCQs With Answer

This quiz set focuses on the determination of acid value in cosmetic products — a key quality parameter in herbal and cosmetic analysis. It covers theory, practical titration steps, sample preparation for creams and emulsions, choice of solvents and indicators, calculation formulae, standardization procedures, common interferences and troubleshooting. These multiple-choice questions are designed for M.Pharm students to reinforce understanding of method principles, laboratory practice and result interpretation. Practically oriented and conceptually deep, the MCQs also include a calculation example to test numerical competence in converting titration data into acid value (mg KOH/g).

Q1. What is the definition of acid value in the context of cosmetic product analysis?

• The mass of free fatty acids per 100 g of product
• The milligrams of KOH required to neutralize free acids in 1 g of sample
• The volume of titrant used to saponify all esters in the sample
• The percentage of free fatty acids by weight

Correct Answer: The milligrams of KOH required to neutralize free acids in 1 g of sample

Q2. What are the usual units reported for acid value?

• mg NaOH per g of sample
• mg KOH per g of sample
• % w/w free fatty acids
• moles of acid per liter

Correct Answer: mg KOH per g of sample

Q3. Which titrant is most commonly used for determination of acid value in cosmetic oils and creams?

• 0.1 N hydrochloric acid in ethanol
• 0.1 N sodium hydroxide in water
• 0.1 N potassium hydroxide in ethanol
• 0.1 N silver nitrate in acetone

Correct Answer: 0.1 N potassium hydroxide in ethanol

Q4. Which indicator is conventionally used for visual end-point detection in acid value titrations?

• Methyl orange
• Phenolphthalein
• Bromothymol blue
• Thymol blue

Correct Answer: Phenolphthalein

Q5. What solvent system is commonly recommended for dissolving cosmetic oils before titration for acid value?

• Water only
• Absolute ethanol or ethanol:diethyl ether (1:1), neutralized
• Acetone:water (1:1)
• Chloroform only

Correct Answer: Absolute ethanol or ethanol:diethyl ether (1:1), neutralized

Q6. Which of the following best explains why a blank titration is performed during acid value determination?

• To neutralize all acids in the sample
• To account for acidity contributed by solvents and reagents
• To calibrate the weighing balance
• To measure the moisture content of the sample

Correct Answer: To account for acidity contributed by solvents and reagents

Q7. What is the correct formula to calculate acid value (AV) from titration data?

• AV = (V × N × 56.1) / W
• AV = (V − Vb) × W / (N × 56.1)
• AV = (V − Vb) × N × 56.1 / W
• AV = (V + Vb) × N / (W × 56.1)

Correct Answer: AV = (V − Vb) × N × 56.1 / W

Q8. In the formula AV = (V − Vb) × N × 56.1 / W, what does Vb represent?

• Volume of titrant used for sample
• Volume of titrant used for standardization
• Volume of titrant used in the blank determination
• Volume of solvent added to the sample

Correct Answer: Volume of titrant used in the blank determination

Q9. Which primary standard is commonly used to standardize the potassium hydroxide titrant before acid value determination?

• Sodium carbonate
• Potassium hydrogen phthalate (KHP)
• Benzoic acid
• Hydrochloric acid

Correct Answer: Potassium hydrogen phthalate (KHP)

Q10. Why should ethanol used for acid value titration be recently neutralized or checked?

• Because ethanol oxidizes free fatty acids
• Because acidic impurities in ethanol can cause a high blank and false high acid value
• Because ethanol will react with KOH to form esters only at high temperature
• Because ethanol increases the sample weight

Correct Answer: Because acidic impurities in ethanol can cause a high blank and false high acid value

Q11. For an emulsion cosmetic (cream) sample, what is the recommended first step before titration for acid value?

• Direct titration without any treatment
• Evaporation of water and direct titration of residue
• Extraction of the lipid phase with an appropriate solvent and analysis of the extract
• Heating the cream to 100 °C to remove preservatives

Correct Answer: Extraction of the lipid phase with an appropriate solvent and analysis of the extract

Q12. How does increasing temperature during titration primarily affect determination of acid value?

• It always improves endpoint sharpness
• It can promote saponification of esters leading to falsely elevated acid values
• It neutralizes acids faster without affecting accuracy
• It reduces the normality of KOH

Correct Answer: It can promote saponification of esters leading to falsely elevated acid values

Q13. Which of the following sample-handling practices helps to minimize change in acid value prior to analysis?

• Store samples at room temperature in open containers
• Store samples protected from air, light and at low temperature
• Expose samples to sunlight for 1–2 hours before analysis
• Heat samples to 60 °C to remove moisture

Correct Answer: Store samples protected from air, light and at low temperature

Q14. Which factor does NOT directly contribute to an increased measured acid value in cosmetic oils?

• Hydrolytic rancidity producing free fatty acids
• Oxidative degradation producing short-chain acids
• Presence of acidic additives deliberately added
• High content of unsaponifiable matter such as sterols

Correct Answer: High content of unsaponifiable matter such as sterols

Q15. What is a principal advantage of potentiometric titration over visual end-point titration for acid value?

• It eliminates the need to extract samples
• It provides a more objective and precise endpoint for colored or opaque samples
• It uses less titrant
• It does not require standardization of titrant

Correct Answer: It provides a more objective and precise endpoint for colored or opaque samples

Q16. If a sample shows a sudden rise in acid value during storage, which is the most likely cause?

• Contamination with basic substances
• Hydrolysis of triglycerides releasing free fatty acids
• Loss of volatile basic impurities
• Increase in unsaponifiable matter

Correct Answer: Hydrolysis of triglycerides releasing free fatty acids

Q17. Which normality of KOH titrant is frequently recommended for routine acid value determinations on cosmetic oils?

• 1.0 N
• 0.5 N
• 0.1 N
• 0.01 N

Correct Answer: 0.1 N

Q18. Which of the following is a common source of error that leads to underestimation of acid value?

• Using an excess of solvent
• Over-titration beyond the endpoint
• Incomplete extraction of free acids from the matrix
• Performing a blank titration

Correct Answer: Incomplete extraction of free acids from the matrix

Q19. Which statement correctly contrasts acid value and saponification value?

• Acid value measures total base required to saponify esters; saponification value measures free acids
• Acid value measures free acids; saponification value measures total amount of esterifiable material (both acid and glycerol equivalents)
• Both values measure the same property and are numerically identical
• Saponification value is used only for aqueous samples while acid value is for oils

Correct Answer: Acid value measures free acids; saponification value measures total amount of esterifiable material (both acid and glycerol equivalents)

Q20. Calculation: A 2.000 g cosmetic oil sample required 3.50 mL of 0.10 N KOH for titration, and the blank consumed 0.10 mL. Using AV = (V − Vb) × N × 56.1 / W, what is the acid value (rounded to two decimals)?

• 0.95 mg KOH/g
• 9.54 mg KOH/g
• 19.08 mg KOH/g
• 1.91 mg KOH/g

Correct Answer: 9.54 mg KOH/g

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