Ester value of oils MCQs With Answer

Ester value of oils MCQs With Answer

The ester value of oils is a key analytical parameter used in pharmaceutical quality control to quantify esterified fatty acids in fats and oils. Designed for B. Pharm students, this introduction explains that ester value (expressed as mg KOH/g) equals the saponification value minus the acid value and is determined by titrimetric methods involving alcoholic KOH, back-titration and indicators like phenolphthalein. Understanding ester value aids in assessing hydrolysis, rancidity, and proper formulation of lipid-based drug products. Mastery of calculations, laboratory procedure and interpretation is essential for excipient testing and research. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is the ester value (number) of an oil?

• The amount of acid in mg KOH required to neutralize free acids
• The amount of KOH in mg required to saponify ester groups per gram of sample
• The weight percent of triglycerides in an oil
• The iodine uptake of the oil

Correct Answer: The amount of KOH in mg required to saponify ester groups per gram of sample

Q2. Which equation correctly relates ester value (EV), saponification value (SV) and acid value (AV)?

• SV = EV – AV
• EV = SV + AV
• EV = SV – AV
• AV = EV + SV

Correct Answer: EV = SV – AV

Q3. What are the common units for reporting ester value?

• mg NaOH/g sample
• mg KOH/g sample
• % w/w
• mg/L

Correct Answer: mg KOH/g sample

Q4. Which reagent is typically used to saponify oils when determining ester value?

• Aqueous HCl
• Alcoholic KOH
• Sodium chloride solution
• Potassium permanganate

Correct Answer: Alcoholic KOH

Q5. During ester value determination, how is excess alkali usually quantified?

• Back-titration with standard acid
• Gravimetric precipitation
• Gas chromatography
• Colorimetric copper assay

Correct Answer: Back-titration with standard acid

Q6. Which indicator is commonly used in titrations for saponification and ester value methods?

• Methyl orange
• Phenolphthalein
• Bromothymol blue
• Starch-iodide

Correct Answer: Phenolphthalein

Q7. If the saponification value of an oil is 220 mg KOH/g and the acid value is 4 mg KOH/g, what is the ester value?

• 224 mg KOH/g
• 216 mg KOH/g
• 220 mg KOH/g
• 4 mg KOH/g

Correct Answer: 216 mg KOH/g

Q8. Ester value provides information primarily about which component of oils?

• Free fatty acids only
• Saponifiable esters such as triglycerides
• Unsaturated bonds
• Trace metals

Correct Answer: Saponifiable esters such as triglycerides

Q9. A bottle of oil shows an increasing acid value with time while the saponification value remains constant. What happens to the ester value?

• Increases
• Decreases
• Remains unchanged
• Becomes zero

Correct Answer: Decreases

Q10. Which process in oils leads to a decrease in ester value?

• Hydrogenation of double bonds
• Hydrolysis (lipolysis) producing free fatty acids
• Saponification to fatty acid salts
• Distillation

Correct Answer: Hydrolysis (lipolysis) producing free fatty acids

Q11. For calculating ester value from titration data, which constant (molar mass equivalent) is used for KOH?

• 40.0
• 56.1
• 18.0
• 98.1

Correct Answer: 56.1

Q12. The general formula used for saponification value calculation is SV = (Vb – Vs) × N × 56.1 / W. What does Vb represent?

• Volume of acid used for sample titration
• Volume of base consumed by the sample
• Volume of alkali used in blank titration
• Volume of solvent used

Correct Answer: Volume of alkali used in blank titration

Q13. If a 1.0 g oil sample required 14.5 mL of 0.5 N HCl for back-titration and the blank required 25.0 mL, what is the saponification value? (Use 56.1)

• 609.5 mg KOH/g
• 561.0 mg KOH/g
• (25.0-14.5)*0.5*56.1 /1.0 = (Correct calculation)
• 310.35 mg KOH/g

Correct Answer: (25.0-14.5)*0.5*56.1 /1.0 = (Correct calculation)

Q14. The ester value is especially useful in the pharmaceutical industry to assess what?

• Purity of inorganic salts
• Quality and hydrolytic breakdown of lipid excipients
• Pigment stability
• Solubility of APIs in water

Correct Answer: Quality and hydrolytic breakdown of lipid excipients

Q15. Which statement is true regarding high ester value in an oil sample?

• Indicates a high proportion of free fatty acids
• Indicates a high proportion of esterified fatty acids (triglycerides)
• Indicates high oxidative rancidity
• Indicates low molecular weight esters only

Correct Answer: Indicates a high proportion of esterified fatty acids (triglycerides)

Q16. During ester value testing, why is a blank titration necessary?

• To measure the acidity of the sample
• To account for KOH consumption by reagents and solvent
• To standardize the indicator
• To calibrate the balance

Correct Answer: To account for KOH consumption by reagents and solvent

Q17. If the acid value of a sample is 8 mg KOH/g and its ester value is 192 mg KOH/g, what is the saponification value?

• 200 mg KOH/g
• 184 mg KOH/g
• 8 mg KOH/g
• 192 mg KOH/g

Correct Answer: 200 mg KOH/g

Q18. Which analytical interference can cause erroneous ester value results?

• Presence of unsaponifiable matter that consumes KOH
• Low iodine number
• Excess water in the titrant
• High refractive index

Correct Answer: Presence of unsaponifiable matter that consumes KOH

Q19. In preparing for ester value titration, why is ethanol often used as solvent?

• It reacts with esters to form new compounds
• It dissolves oils and allows alcoholic KOH to react effectively
• It neutralizes free fatty acids
• It prevents titration endpoints

Correct Answer: It dissolves oils and allows alcoholic KOH to react effectively

Q20. Ester value determination measures esters that on saponification yield what products?

• Free fatty acids and glycerol (or alcohols)
• Carbohydrates and proteins
• Peroxides only
• Chlorides and sulfates

Correct Answer: Free fatty acids and glycerol (or alcohols)

Q21. Which of the following best distinguishes ester value from acid value?

• Ester value measures unsaponifiable matter while acid value measures esters
• Ester value quantifies esterified fatty acids; acid value quantifies free fatty acids
• Both measure the same parameter but use different units
• Acid value measures iodine content

Correct Answer: Ester value quantifies esterified fatty acids; acid value quantifies free fatty acids

Q22. In the laboratory, the reflux time during saponification is important because:

• Longer reflux always reduces ester value
• Incomplete saponification leads to underestimation of saponification and ester values
• Reflux time indicates sample purity
• It affects the acid value only

Correct Answer: Incomplete saponification leads to underestimation of saponification and ester values

Q23. Which instrument is NOT typically required for ester value determination?

• Burette
• Analytical balance
• Gas chromatograph
• Hot plate or water bath for reflux

Correct Answer: Gas chromatograph

Q24. For quality control of oil excipients, a sudden drop in ester value suggests:

• Contamination with non-lipid solvents
• Hydrolytic degradation producing free fatty acids
• Increased saturation of fatty acids
• Higher molecular weight triglycerides

Correct Answer: Hydrolytic degradation producing free fatty acids

Q25. If 0.5 g of oil required 10.0 mL of 0.1 N acid for back-titration and blank required 20.0 mL, what is the saponification value? Use 56.1.

• (20.0-10.0)*0.1*56.1/0.5 = 112.2 mg KOH/g
• (10.0-20.0)*0.1*56.1/0.5 = -112.2 mg KOH/g
• 1122 mg KOH/g
• 56.1 mg KOH/g

Correct Answer: (20.0-10.0)*0.1*56.1/0.5 = 112.2 mg KOH/g

Q26. Which sample handling precaution is important before ester value analysis?

• Store samples at high temperature to remove moisture
• Avoid exposure to moisture and light to prevent hydrolysis and oxidation
• Add strong acid to preserve oils
• Freeze-dry the oil

Correct Answer: Avoid exposure to moisture and light to prevent hydrolysis and oxidation

Q27. In calculation formulas, normality (N) refers to:

• The concentration in mg/L
• The molar concentration adjusted for equivalents relevant to reaction
• The density of the titrant
• The weight percent of solution

Correct Answer: The molar concentration adjusted for equivalents relevant to reaction

Q28. Which of the following will NOT affect the ester value of an oil?

• Extent of hydrolysis
• Formation of free fatty acids
• Presence of glycerol esters
• Color of the bottle

Correct Answer: Color of the bottle

Q29. When performing a back-titration, the endpoint color change with phenolphthalein is:

• From colorless to pink on neutralization of excess base
• From pink to colorless when base is neutralized by acid
• From yellow to red
• No color change occurs

Correct Answer: From pink to colorless when base is neutralized by acid

Q30. A high unsaponifiable matter content can cause which effect on ester value measurement?

• No effect at all
• False decrease in measured ester value due to side reactions
• Causes inflation of acid value but not ester value
• Eliminates the need for blank titration

Correct Answer: False decrease in measured ester value due to side reactions

Q31. Ester value determination is most closely a measure of which functional group in lipids?

• Alcohol groups
• Carboxylic acid esters
• Peroxide groups
• Amide bonds

Correct Answer: Carboxylic acid esters

Q32. If a sample’s saponification value is unusually low compared to literature, possible reasons include:

• Sample contains shorter chain triglycerides
• Incomplete saponification or sample contamination with non-saponifiable matter
• Excessive free fatty acids only
• Higher iodine value

Correct Answer: Incomplete saponification or sample contamination with non-saponifiable matter

Q33. Which quality parameter often reported alongside ester value for oils?

• Viscosity at 100°C
• Saponification value and acid value
• Melting point only
• Optical rotation

Correct Answer: Saponification value and acid value

Q34. For biodiesel analysis, ester value (or ester content) helps to determine:

• Glyceride conversion efficiency in transesterification
• Water content only
• Metal contamination
• Color stability

Correct Answer: Glyceride conversion efficiency in transesterification

Q35. A laboratory blank consumed 12.0 mL acid, while the sample required 7.5 mL. If normality is 0.5 N and sample weight is 1 g, what is the saponification value? (Use 56.1)

• (12.0-7.5)*0.5*56.1 = 125.175 mg KOH/g
• (7.5-12.0)*0.5*56.1 = -125.175 mg KOH/g
• 56.1 mg KOH/g
• 12.0 mg KOH/g

Correct Answer: (12.0-7.5)*0.5*56.1 = 125.175 mg KOH/g

Q36. Which procedural step is essential to prevent CO2 absorption that may affect titration?

• Leave burette open to air
• Use freshly boiled and cooled solvent and avoid prolonged exposure to air
• Add carbonated water to titrant
• Use methyl orange indicator

Correct Answer: Use freshly boiled and cooled solvent and avoid prolonged exposure to air

Q37. What does a low ester value with a low acid value suggest about an oil sample?

• High degree of hydrolysis
• High proportion of unsaponifiable matter or non-lipid diluents
• High triglyceride content
• High moisture content only

Correct Answer: High proportion of unsaponifiable matter or non-lipid diluents

Q38. Which safety precaution is most relevant when working with alcoholic KOH for ester value determination?

• Alcoholic KOH is non-corrosive
• Work in fume hood and use gloves and eye protection due to causticity and flammability
• No special precautions needed
• Only radiation shielding is needed

Correct Answer: Work in fume hood and use gloves and eye protection due to causticity and flammability

Q39. Ester value can be used to monitor the progress of which reaction in lipid processing?

• Hydrogenation of double bonds
• Transesterification to produce biodiesel
• Distillation of essential oils
• Emulsification

Correct Answer: Transesterification to produce biodiesel

Q40. Which of these will reduce the measured ester value without changing the saponification value?

• Increase in free fatty acids
• Contamination with unreactive diluent
• Experimental error in blank only
• Impossible: ester value depends on SV and AV

Correct Answer: Increase in free fatty acids

Q41. Theoretical question: In a perfect triglyceride sample with no free fatty acids, what relationship holds between SV and EV?

• SV = EV
• SV > EV by AV
• EV = 0
• AV = SV + EV

Correct Answer: SV = EV

Q42. When calculating acid value, which titrant and titration direction are used?

• Titrate sample with standard acid until phenolphthalein turns pink
• Titrate sample with standard alkali until color changes from colorless to pink
• Titrate sample with iodine solution
• Titrate blank with base only

Correct Answer: Titrate sample with standard alkali until color changes from colorless to pink

Q43. Which sample property correlates inversely with ester value if hydrolysis occurs?

• Free fatty acid content
• Glyceride content
• Moisture content
• Viscosity

Correct Answer: Glyceride content

Q44. A student obtains SV = 190 mg KOH/g and AV = 6 mg KOH/g. Which statement is correct?

• EV = 184 mg KOH/g and indicates most fatty acids are esterified
• EV = 196 mg KOH/g and sample is mostly free fatty acids
• EV = 190 mg KOH/g regardless of AV
• AV must be subtracted from EV to get SV

Correct Answer: EV = 184 mg KOH/g and indicates most fatty acids are esterified

Q45. Which factor can artificially increase the acid value reading?

• Presence of residual alcohol in sample
• Oxidation producing acidic peroxides
• Evaporation of solvent
• Use of neutral glassware

Correct Answer: Oxidation producing acidic peroxides

Q46. For an exam calculation: If blank volume = 30.0 mL, sample volume = 18.0 mL, normality = 0.5 N, sample weight = 2.0 g, what is SV? (Use 56.1)

• (30.0-18.0)*0.5*56.1 / 2.0 = 168.3 mg KOH/g
• (18.0-30.0)*0.5*56.1 / 2.0 = -168.3 mg KOH/g
• 56.1 mg KOH/g
• 336.6 mg KOH/g

Correct Answer: (30.0-18.0)*0.5*56.1 / 2.0 = 168.3 mg KOH/g

Q47. Which of the following lipids would typically have the highest saponification and thus potentially ester value?

• High molecular weight triglycerides (long-chain fatty acids)
• Short-chain triglycerides
• Free fatty acids only
• Unsaponifiable waxes

Correct Answer: Short-chain triglycerides

Q48. In method validation for ester value, which parameter is critical?

• Linearity of colorimetric response
• Accuracy and precision of titration volumes and normality
• Retention time reproducibility in HPLC
• Membrane pore size

Correct Answer: Accuracy and precision of titration volumes and normality

Q49. Which practical tip improves endpoint detection in ester value titration?

• Use extremely dilute indicators
• Perform titration slowly near endpoint and swirl frequently for clear color change
• Heat the titration flask continuously during titration
• Add excess KOH at endpoint

Correct Answer: Perform titration slowly near endpoint and swirl frequently for clear color change

Q50. Which conclusion is correct if an oil sample has EV = 0 mg KOH/g and AV = 0 mg KOH/g?

• Sample contains only free fatty acids
• Sample likely contains no saponifiable esters and no free acids, possibly inert non-lipids or pure solvent
• Sample is highly esterified triglyceride
• Analytical error always

Correct Answer: Sample likely contains no saponifiable esters and no free acids, possibly inert non-lipids or pure solvent

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