Determination of iodine value MCQs With Answer

Introduction: This set of multiple-choice questions on the determination of iodine value is tailored for M.Pharm students studying Herbal and Cosmetic Analysis (MPA 204T). The iodine value assay is a fundamental quality-control test used to quantify the degree of unsaturation in fats, oils and cosmetic excipients. These MCQs cover the principle, reagents (Wijs and Hanus reagents), procedural steps, titration and calculation, sources of error, typical iodine value ranges for common oils, and alternative analytical approaches. Practicing these questions will strengthen your understanding of method selection, interpretation of results, troubleshooting and practical considerations required for accurate iodine value determination in pharmaceutical and cosmetic contexts.

Q1. What is the iodine value (IV)?

• The amount of iodine (in grams) that reacts with 100 g of fat or oil
• The percentage of free iodine present in an oil
• The mass of iodine required to fully saponify a fat
• The volume of reagent consumed per gram of oil

Correct Answer: The amount of iodine (in grams) that reacts with 100 g of fat or oil

Q2. What is the basic principle of the Wijs method for iodine value determination?

• Oxidation of double bonds to carbonyls followed by permanganate titration
• Addition of iodine halide across C=C double bonds; excess halide is converted to free iodine and titrated iodometrically
• Direct titration of unsaturated bonds with sodium thiosulfate
• Measurement of UV absorbance of conjugated dienes to estimate unsaturation

Correct Answer: Addition of iodine halide across C=C double bonds; excess halide is converted to free iodine and titrated iodometrically

Q3. Which reagent is most commonly referred to as the Wijs reagent?

• Iodine monochloride in glacial acetic acid
• Iodine in potassium iodide solution
• Iodine bromide in water
• Potassium permanganate in acetone

Correct Answer: Iodine monochloride in glacial acetic acid

Q4. What is the role of potassium iodide (KI) in the iodine value procedure?

• To neutralize excess acetic acid
• To react with excess iodine halide and liberate free iodine for titration
• To act as the primary titrant
• To precipitate unsaponifiable matter

Correct Answer: To react with excess iodine halide and liberate free iodine for titration

Q5. Which solution is used to titrate the liberated iodine in the standard iodine value method?

• Standard hydrochloric acid
• Standard sodium thiosulfate solution
• Standard potassium permanganate
• Standard silver nitrate

Correct Answer: Standard sodium thiosulfate solution

Q6. Which indicator is typically used to detect the end point in iodine value titration?

• Phenolphthalein
• Methyl orange
• Starch (forms blue complex with iodine)
• Diphenylamine

Correct Answer: Starch (forms blue complex with iodine)

Q7. Which of the following is the correct formula commonly used to calculate iodine value?

• Iodine value = (Vb − Vs) × N × 126.9 / W
• Iodine value = (Vs − Vb) × N × 12.69 / W
• Iodine value = (Vb − Vs) × N × 12.69 / W
• Iodine value = (Vb + Vs) × N × 0.1269 / W

Correct Answer: Iodine value = (Vb − Vs) × N × 12.69 / W

Q8. In what units is iodine value usually expressed?

• mg I2 per g sample
• g I2 per 100 g sample
• mol I2 per kg sample
• percent iodine by weight

Correct Answer: g I2 per 100 g sample

Q9. A high iodine value for an oil indicates which of the following?

• A high content of saturated fatty acids
• A high degree of unsaturation (more double bonds)
• High moisture content
• High peroxide number

Correct Answer: A high degree of unsaturation (more double bonds)

Q10. Which oil typically has one of the highest iodine values?

• Coconut oil (approx. 7–12)
• Olive oil (approx. 75–90)
• Linseed (flaxseed) oil (approx. 160–190)
• Beef tallow (approx. 30–40)

Correct Answer: Linseed (flaxseed) oil (approx. 160–190)

Q11. Which sample contamination or condition most commonly causes a falsely high iodine value?

• Excess moisture in the solvent
• Presence of pre-existing peroxides or oxidized products
• High content of saturated triglycerides
• Low sample temperature during titration

Correct Answer: Presence of pre-existing peroxides or oxidized products

Q12. Why is glacial acetic acid used as the solvent medium in the Wijs method?

• Because it forms a complex with iodine that is easier to titrate
• To dissolve the reagent and sample and provide an anhydrous medium preventing hydrolysis
• Because it reacts with double bonds to increase sensitivity
• To act as a strong oxidizing agent during the reaction

Correct Answer: To dissolve the reagent and sample and provide an anhydrous medium preventing hydrolysis

Q13. What is the Hanus reagent composed of?

• Iodine monochloride in glacial acetic acid
• Iodine bromide (IBr) in glacial acetic acid
• Iodine dissolved in methanol
• Potassium iodate in water

Correct Answer: Iodine bromide (IBr) in glacial acetic acid

Q14. How should Wijs reagent be stored to maintain its stability?

• In clear glass bottle at room light and temperature
• In a plastic container at high temperature
• In an amber bottle, cool and dark, tightly stoppered to avoid decomposition
• Mixed with water before storage for stability

Correct Answer: In an amber bottle, cool and dark, tightly stoppered to avoid decomposition

Q15. Which modern analytical approach can be used as an alternative to titrimetric iodine value measurement by determining fatty acid composition?

• Ultraviolet-visible spectrophotometry of crude oil
• Gas chromatography of fatty acid methyl esters (GC-FAME) to calculate unsaturation
• Direct gravimetric weighing of double bonds
• Flame photometry

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

Q16. With which standard substance is sodium thiosulfate commonly standardized for iodine-value titrations?

• Potassium dichromate
• Potassium iodate (standard KIO3 solution)
• Standard hydrochloric acid
• Oxalic acid

Correct Answer: Potassium iodate (standard KIO3 solution)

Q17. Why are iodine value determinations usually performed protected from light?

• Light promotes formation of starch complexes
• Light accelerates decomposition of iodine halide reagents and free iodine causing erroneous results
• Light causes precipitation of unsaponifiable matter
• Light increases solubility of oils making titration difficult

Correct Answer: Light accelerates decomposition of iodine halide reagents and free iodine causing erroneous results

Q18. What is the typical color change sequence observed during an iodine value titration when starch is used as indicator?

• Colorless → red → blue
• Yellow-brown (iodine present) → blue after starch addition → colorless at endpoint
• Blue → green → colorless
• Clear → cloudy → clear

Correct Answer: Yellow-brown (iodine present) → blue after starch addition → colorless at endpoint

Q19. A Wijs-method titration gave a blank (Vb) of 25.00 mL, sample titration (Vs) 17.60 mL, thiosulfate normality N = 0.100 N, and sample weight 0.500 g. What is the iodine value (rounded)?

• 18.78 g I2/100 g
• 37.56 g I2/100 g
• 9.39 g I2/100 g
• 25.40 g I2/100 g

Correct Answer: 18.78 g I2/100 g

Q20. Which safety practice is most important when performing iodine value determinations with Wijs reagent?

• Perform the reaction in direct sunlight to speed up reaction
• Use minimal personal protective equipment (PPE) since reagents are non-hazardous
• Work in a fume hood, wear appropriate PPE (gloves, goggles, lab coat) and avoid moisture and skin contact
• Dispose of all reagents down the sink without neutralization

Correct Answer: Work in a fume hood, wear appropriate PPE (gloves, goggles, lab coat) and avoid moisture and skin contact

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