Iodine value of oils MCQs With Answer

Iodine value of oils MCQs With Answer is a focused resource for B. Pharm students studying lipid analysis and pharmaceutical excipients. This introduction explains the iodine value — a key measure of oil unsaturation — and its practical relevance in stability, rancidity, and formulation. Topics covered include Wijs and Hanus methods, titration with sodium thiosulfate, units (g I2/100 g), interpretation for drying vs non-drying oils, and implications for drug stability and topical formulations. These MCQs reinforce theory, analytical technique, common calculation concepts, and error sources encountered in the iodine value test. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What does the iodine value of an oil measure?

• The amount of iodine absorbed by double bonds in fatty acids
• The total peroxide content of the oil
• The free fatty acid percentage
• The molecular weight of triglycerides

Correct Answer: The amount of iodine absorbed by double bonds in fatty acids

Q2. What are the common units used for reporting iodine value?

• Grams of iodine absorbed per 100 grams of sample
• Milligrams of iodine per milliliter
• Percent by volume
• Mol iodine per mole of oil

Correct Answer: Grams of iodine absorbed per 100 grams of sample

Q3. Which reagent is typically used in the Wijs method for iodine value determination?

• Iodine monochloride (ICl) in acetic acid
• Potassium permanganate (KMnO4)
• Chromic acid in sulfuric acid
• Sodium hypochlorite solution

Correct Answer: Iodine monochloride (ICl) in acetic acid

Q4. In the iodine value titration, what is the titrant used to quantify liberated iodine?

• Sodium thiosulfate
• Potassium permanganate
• Sodium hydroxide
• Hydrochloric acid

Correct Answer: Sodium thiosulfate

Q5. Why is potassium iodide (KI) added after reaction with Wijs reagent?

• To convert excess halogen to free iodine for titration
• To neutralize the acetic acid
• To precipitate fatty acids
• To act as an indicator

Correct Answer: To convert excess halogen to free iodine for titration

Q6. Which indicator is commonly used to detect the endpoint in iodine value titration?

• Starch solution
• Phenolphthalein
• Methyl orange
• Litmus paper

Correct Answer: Starch solution

Q7. How does iodine value correlate with degree of unsaturation?

• Higher iodine value indicates more double bonds (higher unsaturation)
• Higher iodine value indicates fewer double bonds
• Iodine value is independent of unsaturation
• Iodine value measures chain length, not unsaturation

Correct Answer: Higher iodine value indicates more double bonds (higher unsaturation)

Q8. Which fatty acid will give the highest iodine value per mole?

• Linolenic acid (three double bonds)
• Linoleic acid (two double bonds)
• Oleic acid (one double bond)
• Stearic acid (no double bond)

Correct Answer: Linolenic acid (three double bonds)

Q9. What type of reaction occurs between iodine reagents and carbon–carbon double bonds in oils?

• Addition across double bonds (halogenation)
• Oxidation to carboxylic acids
• Hydrolysis of esters
• Polymerization of chains

Correct Answer: Addition across double bonds (halogenation)

Q10. Which oil is typically classified as non-drying based on iodine value?

• Olive oil (relatively low iodine value)
• Linseed oil (high iodine value)
• Safflower oil (very high iodine value)
• Sunflower oil (very high iodine value)

Correct Answer: Olive oil (relatively low iodine value)

Q11. The Hanus method uses which halogenating reagent?

• Iodine bromide (IBr) in acetic acid
• Chlorine gas in acetic acid
• Hydrogen bromide
• Potassium iodide

Correct Answer: Iodine bromide (IBr) in acetic acid

Q12. Why is glacial acetic acid used as solvent in some iodine value methods?

• It dissolves oils and stabilizes the halogen reagent without water
• It reacts with double bonds to form esters
• It acts as a base to neutralize acids
• It reduces iodine to iodide

Correct Answer: It dissolves oils and stabilizes the halogen reagent without water

Q13. Which parameter is most directly inferred from iodine value in pharmaceutical formulations?

• Degree of unsaturation affecting oxidative stability
• Acid value affecting pH
• Saponification value indicating molar mass
• Peroxide value indicating immediate rancidity

Correct Answer: Degree of unsaturation affecting oxidative stability

Q14. If an oil has a very high iodine value, what is a likely practical concern for formulations?

• Greater susceptibility to oxidation and rancidity
• Low solubility in lipophilic solvents
• High melting point interfering with handling
• Increased bacterial contamination risk

Correct Answer: Greater susceptibility to oxidation and rancidity

Q15. How does conjugation of double bonds affect iodine value measurement?

• Conjugated double bonds may react differently and give lower apparent iodine uptake
• Conjugation increases iodine uptake linearly
• Conjugation prevents any reaction with halogens
• Conjugation does not influence iodine value at all

Correct Answer: Conjugated double bonds may react differently and give lower apparent iodine uptake

Q16. What is a primary source of error when titrating iodine value?

• Exposure to light and air causing oxidative losses
• Using too much starch indicator
• Overheating below 10°C
• Excess sample lipid concentration causing immediate endpoint

Correct Answer: Exposure to light and air causing oxidative losses

Q17. How is iodine value practically useful for distinguishing oils?

• It helps classify oils as drying, semi-drying, or non-drying based on unsaturation
• It gives exact fatty acid chain lengths
• It measures water content in oils
• It indicates bacterial contamination level

Correct Answer: It helps classify oils as drying, semi-drying, or non-drying based on unsaturation

Q18. What is the role of blank determination in iodine value experiments?

• To account for reagent consumption by solvents and reagents alone
• To standardize temperature
• To adjust pH of the mixture
• To remove dissolved oxygen

Correct Answer: To account for reagent consumption by solvents and reagents alone

Q19. How does temperature control influence iodine value measurement?

• Higher temperatures can increase side reactions and affect accuracy
• Temperature has no effect on the halogen addition
• Lower temperatures always increase iodine uptake
• Only boiling temperatures are relevant

Correct Answer: Higher temperatures can increase side reactions and affect accuracy

Q20. Which statement best differentiates iodine value from peroxide value?

• Iodine value measures unsaturation; peroxide value measures primary oxidation products
• Both measure the same chemical property
• Iodine value measures acidity; peroxide value measures unsaturation
• Iodine value measures water; peroxide value measures solids

Correct Answer: Iodine value measures unsaturation; peroxide value measures primary oxidation products

Q21. In calculation of iodine value, which of the following is required?

• Volume and normality of titrant, sample weight, and blank correction
• Only sample weight
• Density of the oil and melting point
• Saponification number and acid value

Correct Answer: Volume and normality of titrant, sample weight, and blank correction

Q22. Which fatty acid would contribute the least to iodine value in a triglyceride?

• Stearic acid (no double bonds)
• Oleic acid (one double bond)
• Linoleic acid (two double bonds)
• Linolenic acid (three double bonds)

Correct Answer: Stearic acid (no double bonds)

Q23. What precaution is important when storing reagents for iodine value tests?

• Keep reagents in dark, cool containers to prevent decomposition
• Store reagents in direct sunlight for activation
• Freeze reagents to increase reactivity
• Mix reagents with water to stabilize them

Correct Answer: Keep reagents in dark, cool containers to prevent decomposition

Q24. Which structural feature decreases iodine uptake despite presence of double bonds?

• Conjugation or hindered double bonds (steric hindrance)
• Terminal double bonds
• Short chain length only
• High oxygen content in molecule

Correct Answer: Conjugation or hindered double bonds (steric hindrance)

Q25. How is iodine value relevant when selecting an oil for topical pharmaceutical products?

• Iodine value indicates propensity for oxidative rancidity affecting shelf life
• Iodine value determines antibacterial activity
• Iodine value measures emulsification capacity directly
• Iodine value indicates viscosity at room temperature

Correct Answer: Iodine value indicates propensity for oxidative rancidity affecting shelf life

Q26. Which of the following oils typically has the highest iodine value?

• Linseed oil (rich in polyunsaturated fatty acids)
• Coconut oil (rich in saturated fatty acids)
• Palm oil (moderately saturated)
• Beef tallow (saturated animal fat)

Correct Answer: Linseed oil (rich in polyunsaturated fatty acids)

Q27. If the blank titration consumes more thiosulfate than expected, what does this indicate?

• Contaminated reagents or reagent degradation
• Sample contained no unsaturation
• Indicator was not used
• Sample weight was too low

Correct Answer: Contaminated reagents or reagent degradation

Q28. What is the effect of hydrogenation on the iodine value of vegetable oil?

• Iodine value decreases as double bonds are reduced to single bonds
• Iodine value increases due to chain shortening
• Iodine value remains unchanged
• Iodine value fluctuates unpredictably

Correct Answer: Iodine value decreases as double bonds are reduced to single bonds

Q29. How can iodine value help estimate average unsaturation of a mixed oil?

• By providing an aggregate measure proportional to total double bonds per 100 g
• By giving exact mole percent of each fatty acid
• By indicating peroxide concentrations
• By measuring triglyceride molecular weight

Correct Answer: By providing an aggregate measure proportional to total double bonds per 100 g

Q30. Which procedural step neutralizes excess acid before titration in some protocols?

• Adding potassium iodide followed by water and dilution
• Adding sodium hydroxide to neutralize completely
• Boiling to evaporate acetic acid
• Adding chloroform to absorb acid

Correct Answer: Adding potassium iodide followed by water and dilution

Q31. Why is chloroform or carbon tetrachloride sometimes used in iodine value tests?

• As a solvent to dissolve oil and permit uniform reaction
• To react with double bonds and form chlorides
• To act as an internal standard for titration
• To neutralize the Wijs reagent

Correct Answer: As a solvent to dissolve oil and permit uniform reaction

Q32. Which statement about the relationship between iodine value and saponification value is correct?

• They measure different properties: unsaturation vs average chain length, but both characterize oils
• They are identical measurements expressed differently
• Higher saponification value always means higher iodine value
• Iodine value is used to calculate saponification value directly

Correct Answer: They measure different properties: unsaturation vs average chain length, but both characterize oils

Q33. What safety precaution is important when handling Wijs reagent?

• Use in a fume hood and avoid skin contact because it is corrosive and releases halogens
• Store near heat sources to maintain reactivity
• Mix with water immediately to dilute
• Use without gloves to judge odor

Correct Answer: Use in a fume hood and avoid skin contact because it is corrosive and releases halogens

Q34. In a sample containing conjugated dienes, what modification may be necessary?

• Use alternative methods or corrective factors because conjugation affects halogen addition
• Ignore conjugation as it enhances reaction predictably
• Increase titrant normality only
• Dilute the sample to zero concentration

Correct Answer: Use alternative methods or corrective factors because conjugation affects halogen addition

Q35. Which analytical observation suggests incomplete reaction of reagent with oil double bonds?

• Low iodine uptake compared with expected composition
• Immediate clear solution after reagent addition
• No change in blank titration
• Rapid disappearance of starch-blue color before titration

Correct Answer: Low iodine uptake compared with expected composition

Q36. When converting titration results to iodine value, why is blank correction necessary?

• To subtract reagent consumption not due to sample unsaturation
• To increase the final iodine value arbitrarily
• To account for sample moisture content only
• To match results with saponification value

Correct Answer: To subtract reagent consumption not due to sample unsaturation

Q37. Which of the following best describes a drying oil in terms of iodine value?

• An oil with relatively high iodine value and propensity to polymerize on air exposure
• An oil with very low iodine value used for cooking
• An oil that contains no fatty acids
• An oil resistant to oxidation and drying

Correct Answer: An oil with relatively high iodine value and propensity to polymerize on air exposure

Q38. How does cis vs trans geometry of double bonds affect iodine value?

• Iodine value measures number of double bonds and is less affected by cis/trans geometry, though reactivity can differ
• Trans bonds do not react with iodine reagents at all
• Cis geometry doubles the iodine value compared to trans
• Iodine value directly indicates the percent of trans isomers

Correct Answer: Iodine value measures number of double bonds and is less affected by cis/trans geometry, though reactivity can differ

Q39. For a triglyceride sample, what does a moderate iodine value indicate?

• A mix of saturated and unsaturated fatty acids
• Pure saturated fatty acids only
• Only polyunsaturated fatty acids
• Contamination with inorganic salts

Correct Answer: A mix of saturated and unsaturated fatty acids

Q40. What is a practical lab tip to improve accuracy in iodine value titration?

• Perform titration promptly after addition of KI and avoid long delays to minimize side reactions
• Omit the blank determination to save time
• Never use starch indicator because it interferes
• Heat strongly to speed up the reaction

Correct Answer: Perform titration promptly after addition of KI and avoid long delays to minimize side reactions

Q41. Which factor can artificially raise measured iodine value?

• Presence of compounds that react with halogens other than double bonds
• Complete saturation of all double bonds
• Excess sample dilution
• Low reagent purity that reduces halogen availability

Correct Answer: Presence of compounds that react with halogens other than double bonds

Q42. Why might a pharmaceutical analyst compare iodine value with fatty acid profile data?

• To validate unsaturation estimates and detect adulteration
• To measure water content in the oil
• To calculate drug potency directly
• To determine viscosity of oil at 0°C

Correct Answer: To validate unsaturation estimates and detect adulteration

Q43. In which scenario is iodine value NOT a sufficient test by itself?

• When the oil contains halogen-reactive impurities or conjugated systems
• When only saturation level is needed
• When confirming presence of double bonds qualitatively
• When deciding if oil is edible based on taste

Correct Answer: When the oil contains halogen-reactive impurities or conjugated systems

Q44. How does the presence of oxygen-containing functional groups (e.g., epoxides) influence iodine value?

• Epoxidation reduces the number of free double bonds and lowers iodine value
• Epoxides increase iodine uptake equally
• Oxygen groups do not affect iodine value at all
• They automatically convert iodine to iodide without titration

Correct Answer: Epoxidation reduces the number of free double bonds and lowers iodine value

Q45. Which analytical technique can complement iodine value to fully characterize unsaturation?

• Gas chromatography of fatty acid methyl esters (GC-FAME)
• UV-Vis absorbance at 400 nm for color
• Gravimetric determination of ash
• pH titration with NaOH

Correct Answer: Gas chromatography of fatty acid methyl esters (GC-FAME)

Q46. What does a decrease in iodine value over time in stored oil indicate?

• Possible oxidative degradation or polymerization reducing detectable double bonds
• Improved oil quality due to saturation increase
• Contamination with inert solids
• Addition of more unsaturated oil

Correct Answer: Possible oxidative degradation or polymerization reducing detectable double bonds

Q47. Which of the following is a limitation of the iodine value method?

• It cannot distinguish types of double bonds or their positions
• It gives exact positions of double bonds
• It measures only free fatty acids
• It quantifies triglyceride molecular weight precisely

Correct Answer: It cannot distinguish types of double bonds or their positions

Q48. In a standardized iodine value calculation, why is normality of thiosulfate important?

• Because it directly affects the conversion from titre to grams of iodine consumed
• Because normality determines solvent polarity
• Because higher normality increases oil solubility
• Because it calibrates the starch indicator color

Correct Answer: Because it directly affects the conversion from titre to grams of iodine consumed

Q49. What is the likely iodine value trend going from stearic → oleic → linoleic → linolenic acids?

• Increasing iodine value corresponding to increasing number of double bonds
• Decreasing iodine value with more double bonds
• No change across these fatty acids
• Random fluctuations unrelated to double bond count

Correct Answer: Increasing iodine value corresponding to increasing number of double bonds

Q50. For a B. Pharm student, why is understanding iodine value important in pharmaceutical analysis?

• It informs excipient selection, stability prediction, and quality control of lipid-based formulations
• It replaces all other quality tests
• It is only relevant for food scientists, not pharmacists
• It directly measures active pharmaceutical ingredient potency

Correct Answer: It informs excipient selection, stability prediction, and quality control of lipid-based formulations

Download