Acid value of oils MCQs With Answer

Introduction: The acid value of oils MCQs With Answer is a focused study tool for B.Pharm students learning pharmaceutical oils, quality control, and stability testing. Acid value quantifies free fatty acids (FFA) and is expressed as mg KOH/g; it is determined by titration and influences drug stability, irritation potential, and shelf life. Mastery of titration technique, calculations (acid value formula), indicators, solvents, conversion to %FFA (as oleic acid), and relationships with saponification and peroxide values is essential for lab accuracy and pharmacopeial compliance. This set goes deeper into theory, method errors, and interpretation. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is the definition of acid value (acid number) for oils?

• The number of acidic functional groups per molecule
• The mg of free fatty acids present per 100 g of oil
• The mg of potassium hydroxide required to neutralize the free fatty acids in 1 g of sample
• The percentage of saponifiable matter in 1 g of oil

Correct Answer: The mg of potassium hydroxide required to neutralize the free fatty acids in 1 g of sample

Q2. Which unit is commonly used to report acid value?

• % w/w
• mg KOH/g
• mEq/kg
• mg NaOH/g

Correct Answer: mg KOH/g

Q3. Which reagent is conventionally used as titrant in the standard acid value titration?

• Standardized hydrochloric acid in ethanol
• Standardized sulfuric acid in methanol
• Standardized alcoholic potassium hydroxide (KOH)
• Standardized sodium chloride solution

Correct Answer: Standardized alcoholic potassium hydroxide (KOH)

Q4. Which indicator is most frequently used for visual end-point detection in acid value titration?

• Methyl orange
• Phenolphthalein
• Bromothymol blue
• Thymol blue

Correct Answer: Phenolphthalein

Q5. What solvent is typically used to dissolve oils for acid value titration?

• Water alone
• Absolute ethanol or ethanol-ether mixture
• Acetone only
• Concentrated nitric acid

Correct Answer: Absolute ethanol or ethanol-ether mixture

Q6. Which of the following formulas correctly calculates acid value?

• Acid value = (V × N × 56.1) / W
• Acid value = (V × W × 56.1) / N
• Acid value = (N × W) / (V × 56.1)
• Acid value = (V + N + W) / 56.1

Correct Answer: Acid value = (V × N × 56.1) / W

Q7. In the formula Acid value = (V × N × 56.1) / W, what does V represent?

• Volume of sample (mL)
• Volume of KOH titrant used (mL)
• Weight of sample (g)
• Normality of sample

Correct Answer: Volume of KOH titrant used (mL)

Q8. In the acid value formula, what is the meaning of N?

• Normality of KOH titrant
• Number of free fatty acid molecules
• Neutralization pH
• Number of equivalents in sample

Correct Answer: Normality of KOH titrant

Q9. Why is 56.1 used in the acid value calculation?

• It is the molar mass of oleic acid
• It is the equivalent weight of KOH in mg/mmol (molar mass of KOH ≈ 56.1 g/mol)
• It is the boiling point of ethanol
• It is a constant related to saponification

Correct Answer: It is the equivalent weight of KOH in mg/mmol (molar mass of KOH ≈ 56.1 g/mol)

Q10. If 0.5 g of oil requires 2.5 mL of 0.1 N KOH, what is the acid value? (Use 56.1)

• 5.61 mg KOH/g
• 28.05 mg KOH/g
• 14.025 mg KOH/g
• 2.805 mg KOH/g

Correct Answer: 28.05 mg KOH/g

Q11. How is % free fatty acid (as oleic acid) approximately related to acid value?

• %FFA ≈ Acid value × 2.0
• %FFA ≈ Acid value × 0.503
• %FFA ≈ Acid value / 0.503
• %FFA ≈ Acid value × 56.1

Correct Answer: %FFA ≈ Acid value × 0.503

Q12. An oil sample has acid value 10 mg KOH/g. What is approximate %FFA as oleic acid?

• 0.503%
• 5.03%
• 10.0%
• 50.3%

Correct Answer: 5.03%

Q13. Which change in acid value indicates hydrolytic rancidity in oils?

• Decrease in acid value over time
• No change in acid value
• Increase in acid value over time
• Oscillation without trend

Correct Answer: Increase in acid value over time

Q14. Which process primarily produces free fatty acids in stored oils?

• Hydrogenation
• Hydrolytic cleavage of triglycerides by water and lipases
• Complete saponification
• Photochemical cross-linking

Correct Answer: Hydrolytic cleavage of triglycerides by water and lipases

Q15. Which of the following factors most directly increases acid value during storage?

• Low moisture
• Presence of water and microbial or enzymatic activity
• Storage at low temperature under inert gas
• Addition of antioxidants

Correct Answer: Presence of water and microbial or enzymatic activity

Q16. Which test measures saponifiable matter (saponification value) and is related but different from acid value?

• Peroxide value
• Iodine value
• Saponification value (mg KOH/g required to saponify triglycerides)
• Refractive index measurement

Correct Answer: Saponification value (mg KOH/g required to saponify triglycerides)

Q17. If acid value is very high but saponification value is unchanged, what is the most likely explanation?

• Oxidative rancidity only
• Hydrolytic cleavage producing FFA without changing total saponifiable groups
• Loss of glycerol from triglyceride backbone
• Polymerization of fatty acids

Correct Answer: Hydrolytic cleavage producing FFA without changing total saponifiable groups

Q18. Which analytical method gives more precise end-point detection for acid value than visual phenolphthalein titration?

• Refractometry
• Potentiometric titration (pH or mV endpoint)
• Colorimetry at 520 nm
• Gravimetric titration

Correct Answer: Potentiometric titration (pH or mV endpoint)

Q19. During acid value determination, why is anhydrous ethanol often used instead of water?

• Ethanol increases hydrolysis during titration
• Ethanol dissolves oils and avoids water that would hydrolyze triglycerides during analysis
• Ethanol is cheaper than water
• Ethanol reacts with KOH to give a colored product

Correct Answer: Ethanol dissolves oils and avoids water that would hydrolyze triglycerides during analysis

Q20. Which common error will lead to a falsely high acid value?

• Using lower sample weight than recorded in calculation
• Failing to blank the titration (not subtracting blank)
• Using freshly standardized titrant
• Using inert atmosphere during titration

Correct Answer: Failing to blank the titration (not subtracting blank)

Q21. What is the purpose of performing a blank titration in acid value determination?

• To neutralize the sample
• To correct for acidity of solvents, reagents, or apparatus
• To measure saponification value simultaneously
• To calibrate the phenolphthalein color intensity

Correct Answer: To correct for acidity of solvents, reagents, or apparatus

Q22. Which fatty acid standard is commonly used for expressing %FFA in many pharmacopeial monographs?

• Palmitic acid
• Oleic acid
• Linoleic acid
• Stearic acid

Correct Answer: Oleic acid

Q23. How does peroxide value complement acid value in assessing oil quality?

• Peroxide value measures free fatty acids directly
• Peroxide value indicates primary oxidation (peroxides) while acid value indicates hydrolysis/rancidity
• Peroxide value measures water content
• Peroxide value reflects pH of the oil

Correct Answer: Peroxide value indicates primary oxidation (peroxides) while acid value indicates hydrolysis/rancidity

Q24. Which of the following statements about acid value and edible oils is correct?

• Higher acid value improves flavor and shelf life
• Higher acid value indicates hydrolytic rancidity and poor quality
• Acid value is irrelevant to human consumption
• Lower acid value always indicates contamination

Correct Answer: Higher acid value indicates hydrolytic rancidity and poor quality

Q25. In a potentiometric acid value titration, what is typically monitored to detect endpoint?

• Change in turbidity
• Change in pH or electrode potential (mV)
• Change in viscosity
• Change in refractive index

Correct Answer: Change in pH or electrode potential (mV)

Q26. For accuracy, how should KOH titrant be standardized before use?

• By titrating against a primary standard acid like potassium hydrogen phthalate
• By measuring its density only
• By using a pH meter to set pH 7
• By diluting with water until clear

Correct Answer: By titrating against a primary standard acid like potassium hydrogen phthalate

Q27. Which analytical precaution reduces errors from CO2 absorption when preparing KOH titrant?

• Prepare titrant in open beaker overnight
• Standardize titrant immediately before use and store under CO2-free conditions (stoppered)
• Add phenolphthalein to titrant
• Use titrant at elevated temperature

Correct Answer: Standardize titrant immediately before use and store under CO2-free conditions (stoppered)

Q28. When comparing two oil samples, sample A has acid value 1.5 mg KOH/g and sample B 10 mg KOH/g. Which is more degraded by hydrolysis?

• Sample A
• Sample B
• Both are equally degraded
• Cannot tell without iodine value

Correct Answer: Sample B

Q29. Why might an analyst heat a sample briefly before titration when determining acid value?

• To evaporate volatile free fatty acids intentionally
• To dissolve the sample and ensure complete mixing and dissolution of oil in solvent
• To increase the acidity artificially
• To oxidize peroxides prior to titration

Correct Answer: To dissolve the sample and ensure complete mixing and dissolution of oil in solvent

Q30. Which pharmacopeial consideration is associated with acid value testing of pharmaceutical oils?

• Acid value is not mentioned in pharmacopeia
• Limits and methods for acid value may be specified for specific oils to ensure quality
• Pharmacopeia requires acid value to be reported in % w/v only
• Pharmacopeia mandates only peroxide value for oils

Correct Answer: Limits and methods for acid value may be specified for specific oils to ensure quality

Q31. In calculation practice, if blank titration used 0.2 mL of 0.1 N KOH and sample titration used 2.7 mL, which volume is used for V in formula?

• 2.7 mL only
• 0.2 mL only
• 2.7 + 0.2 = 2.9 mL
• 2.7 − 0.2 = 2.5 mL (corrected volume)

Correct Answer: 2.7 − 0.2 = 2.5 mL (corrected volume)

Q32. Which of the following oils would you expect to have naturally low acid value when freshly extracted and well-refined?

• Unrefined used frying oil
• Freshly refined pharmaceutical-grade sunflower oil
• Hydrolyzed oil intentionally processed with lipase
• Oil contaminated with water and microorganisms

Correct Answer: Freshly refined pharmaceutical-grade sunflower oil

Q33. Which analytical interference could cause a falsely low acid value?

• Incomplete dissolution of the oil sample in solvent
• Using an excess of KOH titrant
• Correct blank subtraction
• Accurate titrant standardization

Correct Answer: Incomplete dissolution of the oil sample in solvent

Q34. When converting acid value to meq/g, which conversion is correct? (1 meq KOH = 56.1 mg KOH)

• meq/g = acid value × 56.1
• meq/g = acid value / 56.1
• meq/g = acid value × 0.503
• meq/g = acid value × W

Correct Answer: meq/g = acid value / 56.1

Q35. For quality control, why is monitoring acid value important in topical pharmaceutical oil formulations?

• Acid value determines flavor only
• High acid value may cause skin irritation, affect stability and drug compatibility
• Acid value controls the color of the formulation exclusively
• Acid value prevents drug absorption through the skin

Correct Answer: High acid value may cause skin irritation, affect stability and drug compatibility

Q36. Which instrument-based titration is preferred for automatic and reproducible acid value determinations in QC labs?

• Manual burette with eye observation
• Automatic potentiometric titrator
• Handheld pH strips only
• Gas chromatograph

Correct Answer: Automatic potentiometric titrator

Q37. If an oil contains free fatty acids predominantly as lauric acid (MW 200.32), which statement about conversion from acid value to %FFA is true?

• The conversion factor 0.503 (for oleic) would be exact
• The conversion factor must change because different acid MW gives different %FFA per mg KOH
• No conversion is necessary because acid value equals %FFA directly
• Conversion depends only on saponification value

Correct Answer: The conversion factor must change because different acid MW gives different %FFA per mg KOH

Q38. What is the expected color change at phenolphthalein end point during titration of an acidic oil solution?

• Colorless to pink (faint permanent pink)
• Yellow to red
• Blue to green
• No color change

Correct Answer: Colorless to pink (faint permanent pink)

Q39. Which safety precaution is important when performing acid value titration with alcoholic KOH?

• Avoid using gloves because KOH is harmless
• Work in well-ventilated area; KOH and ethanol are caustic and flammable—use PPE
• Store titrant in open container to keep fresh
• Heat strongly to speed titration

Correct Answer: Work in well-ventilated area; KOH and ethanol are caustic and flammable—use PPE

Q40. In which situation would acid value decrease artificially during analysis?

• CO2 absorption by titrant
• Evaporation of volatile free fatty acids before titration
• Incomplete neutralization
• Using a higher normality titrant

Correct Answer: Evaporation of volatile free fatty acids before titration

Q41. Which of the following best explains why distilled water is avoided in the sample solvent for acid value titration?

• Water increases solubility of triglycerides
• Water can hydrolyze esters during preparation and change acid value
• Water reacts with KOH to form phenolphthalein
• Water reduces the equivalence weight of KOH

Correct Answer: Water can hydrolyze esters during preparation and change acid value

Q42. How does refining affect acid value of edible or pharmaceutical oils?

• Refining typically increases acid value dramatically
• Refining aims to reduce free fatty acids and lower acid value
• Refining has no effect on acid value
• Refining converts all fatty acids to peroxides

Correct Answer: Refining aims to reduce free fatty acids and lower acid value

Q43. If a sample contains naturally occurring strong acids or acidic additives, what will be the effect on measured acid value?

• Measured acid value will reflect only free fatty acids
• Measured acid value may be falsely elevated because titration measures total acidity
• Measured acid value will be decreased
• Measured acid value is unaffected because reagents ignore other acids

Correct Answer: Measured acid value may be falsely elevated because titration measures total acidity

Q44. Which quality control practice should be done routinely to ensure reliable acid value data in a QC lab?

• Never standardize titrant
• Standardize titrant regularly, run blanks, use duplicate analyses and reference materials
• Only perform titrations when results are needed urgently
• Use expired reagents to save cost

Correct Answer: Standardize titrant regularly, run blanks, use duplicate analyses and reference materials

Q45. What role does temperature play in acid value determination?

• Temperature has no effect on titration chemistry
• Higher temperatures may change solubility and reaction rates; method usually specifies temperature for consistency
• Only freezing the sample affects results
• Temperature changes the molecular weight of KOH

Correct Answer: Higher temperatures may change solubility and reaction rates; method usually specifies temperature for consistency

Q46. Which of the following is NOT true about acid value?

• It measures total free acidity due to free fatty acids
• It can be used to monitor oil degradation during storage
• It measures oxidative degradation products like peroxides directly
• It is expressed as mg KOH required per gram of sample

Correct Answer: It measures oxidative degradation products like peroxides directly

Q47. A student mistakenly used NaOH instead of KOH titrant but applied the same formula using 56.1. How will this affect the computed acid value? (NaOH MW ≈ 40)

• Computed acid value will be correct
• Computed acid value will be erroneously low because the factor 56.1 is for KOH
• Computed acid value will be erroneously high because NaOH is stronger
• There is no difference between NaOH and KOH in calculations

Correct Answer: Computed acid value will be erroneously low because the factor 56.1 is for KOH

Q48. Which sample pre-treatment step can prevent artificial increase of acid value during analysis?

• Exposing sample to moist air before titration
• Removing water by drying sample over anhydrous sodium sulfate or drying agent if necessary
• Adding small amount of acid to stabilize
• Heating sample to dryness at high temperature

Correct Answer: Removing water by drying sample over anhydrous sodium sulfate or drying agent if necessary

Q49. In pharmaceutical method validation for acid value, which parameter is important to demonstrate?

• Linearity, accuracy, precision, limit of detection are irrelevant
• Accuracy, precision (repeatability), linearity and robustness should be established
• Only the time to perform the titration
• Only the color of phenolphthalein

Correct Answer: Accuracy, precision (repeatability), linearity and robustness should be established

Q50. Which interpretation is correct when both peroxide value and acid value of an oil are high?

• The oil has only undergone hydrolytic rancidity
• The oil has experienced both oxidative and hydrolytic degradation or mixed rancidity
• The oil is freshly refined and of high quality
• No meaningful conclusion can be drawn

Correct Answer: The oil has experienced both oxidative and hydrolytic degradation or mixed rancidity

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