Determination of peroxide value MCQs With Answer

Determination of peroxide value MCQs With Answer is a concise quiz resource tailored for M.Pharm students studying Herbal and Cosmetic Analysis (MPA 204T). This set focuses on the analytical principles, practical steps, calculations, and limitations of peroxide value (PV) determination — a key test for assessing primary lipid oxidation in herbal oils, cosmetic ingredients, and formulations. The questions cover iodometric titration, reagents and solvents, calculation formulae, interferences, alternative assays, and interpretation of results in a pharmaceutical context. Use these MCQs to strengthen conceptual understanding, prepare for exams, and reinforce proper laboratory practices for accurate peroxide value measurement.

Q1. What is the fundamental chemical principle behind the classical iodometric determination of peroxide value?

• Oxidation of iodide to iodine by peroxides and titration of liberated iodine with thiosulfate
• Direct titration of peroxides with potassium permanganate
• Reduction of peroxides by ascorbic acid followed by spectrophotometry
• Formation of coloured complexes between peroxides and ferric ions

Correct Answer: Oxidation of iodide to iodine by peroxides and titration of liberated iodine with thiosulfate

Q2. Which solvent system is most commonly recommended for dissolving oil samples in the classical peroxide value titration?

• Water–ethanol (1:1)
• Acetone–water (1:1)
• Acetic acid–chloroform (3:2)
• Methanol–benzene (1:1)

Correct Answer: Acetic acid–chloroform (3:2)

Q3. In the iodometric PV method, what is the role of potassium iodide (KI)?

• It acts as a free-radical scavenger to stabilize peroxides
• It provides iodide ions that are oxidized by hydroperoxides to liberate iodine
• It functions as the titrant to quantify liberated iodine
• It precipitates interfering metal ions

Correct Answer: It provides iodide ions that are oxidized by hydroperoxides to liberate iodine

Q4. According to the stoichiometry of the iodometric PV assay, how many moles of sodium thiosulfate react with one mole of hydroperoxide (ROOH)?

• 0.5 mole
• 1 mole
• 2 moles
• 4 moles

Correct Answer: 2 moles

Q5. What are the conventional units used to express peroxide value in oils and fats?

• mg free fatty acid per g sample
• milliequivalents of active oxygen per kilogram (meq O2/kg)
• absorbance units at 500 nm
• percent peroxides (w/w %)

Correct Answer: milliequivalents of active oxygen per kilogram (meq O2/kg)

Q6. Which formula correctly represents the calculation of peroxide value from titration data?

• PV = (S − B) × N × 100 / W
• PV = (S − B) × N × 1000 / W
• PV = (S + B) × N / W
• PV = (B − S) × N × 1000 / W

Correct Answer: PV = (S − B) × N × 1000 / W

Q7. Why is a blank determination essential when performing peroxide value titration?

• To determine the moisture content of the oil
• To correct for iodine liberated from reagents and background oxidants
• To titrate lipophilic antioxidants present in the sample
• To standardize the starch indicator concentration

Correct Answer: To correct for iodine liberated from reagents and background oxidants

Q8. Which indicator is typically used to detect the endpoint of the titration in the iodometric peroxide value method?

• Phenolphthalein
• Methyl orange
• Starch solution that gives a blue colour with iodine
• Bromothymol blue

Correct Answer: Starch solution that gives a blue colour with iodine

Q9. How do trace metal contaminants such as iron or copper generally affect peroxide value measurements and the oxidation process?

• They act as antioxidants, reducing PV readings
• They catalyse lipid peroxidation, increasing peroxide formation
• They have no effect on peroxide formation
• They precipitate peroxides, making them undetectable

Correct Answer: They catalyse lipid peroxidation, increasing peroxide formation

Q10. The FOX assay (ferrous oxidation–xylenol orange) is an alternative to iodometric PV. What is its basic principle?

• Peroxides reduce ferric to ferrous ion and the ferrous forms a coloured complex with xylenol orange
• Peroxides oxidize ferrous to ferric ion, and ferric ion forms a coloured complex with xylenol orange
• Peroxides directly react with xylenol orange producing fluorescence
• Peroxides form a precipitate with ferrous sulfate that is weighed

Correct Answer: Peroxides oxidize ferrous to ferric ion, and ferric ion forms a coloured complex with xylenol orange

Q11. Which type of substance present in a sample can cause a falsely low peroxide value by consuming liberated iodine?

• Reducing agents such as ascorbic acid or sulfites
• Neutral oils with no unsaturation
• Inert fillers like microcrystalline cellulose
• Trace amounts of water

Correct Answer: Reducing agents such as ascorbic acid or sulfites

Q12. How does peroxide value typically change over time during oxidative deterioration of oils under storage?

• PV steadily decreases from the start of oxidation
• PV first increases as hydroperoxides form, then may decrease as they decompose to secondary products
• PV remains constant while secondary products increase
• PV immediately reflects secondary oxidation products only

Correct Answer: PV first increases as hydroperoxides form, then may decrease as they decompose to secondary products

Q13. Which primary standard is commonly used to standardize sodium thiosulfate solution for PV titrations?

• Potassium permanganate
• Potassium hydrogen phthalate
• Potassium iodate (KIO3)
• Oxalic acid

Correct Answer: Potassium iodate (KIO3)

Q14. Compared to classical titrimetric PV, what is a major advantage of spectrophotometric or colourimetric peroxide assays?

• They are always less sensitive but more precise
• They require larger sample sizes and are slower
• They are generally more sensitive and suitable for low peroxide concentrations
• They eliminate all matrix interferences without sample cleanup

Correct Answer: They are generally more sensitive and suitable for low peroxide concentrations

Q15. Why are PV determinations typically performed using amber glassware or in the dark?

• To maintain constant temperature for titration
• To prevent light-induced formation or decomposition of peroxides
• To avoid evaporation of chloroform
• To prevent starch indicator degradation only

Correct Answer: To prevent light-induced formation or decomposition of peroxides

Q16. In a standard iodometric PV procedure, after adding potassium iodide to the acidified oil solution, what is the recommended immediate step?

• Heat the mixture to 60 °C for 15 minutes
• Allow it to stand in the dark briefly to ensure complete liberation of iodine
• Directly titrate without delay while shaking vigorously
• Add starch indicator before waiting for any reaction

Correct Answer: Allow it to stand in the dark briefly to ensure complete liberation of iodine

Q17. Which aspect of lipid oxidation does the peroxide value specifically quantify?

• Secondary oxidation products such as aldehydes and ketones
• Total unsaturation (double bonds) in fatty acids
• Primary oxidation products, mainly hydroperoxides
• Degree of polymerization of triglycerides

Correct Answer: Primary oxidation products, mainly hydroperoxides

Q18. An aged oil sample smells rancid but shows a low peroxide value. What explains this observation?

• Hydroperoxides have decomposed into secondary oxidation products that cause odor
• The PV method is not sensitive to any oxidation products
• The oil contains strong antioxidants preventing all oxidation
• Rancid odour is unrelated to oxidation

Correct Answer: Hydroperoxides have decomposed into secondary oxidation products that cause odor

Q19. Which normality of sodium thiosulfate is commonly used for titration in many peroxide value procedures to balance sensitivity and ease of titration?

• 0.001 N
• 0.01 N
• 0.5 N
• 1.0 N

Correct Answer: 0.01 N

Q20. To obtain a more complete assessment of oxidative status in oils, which additional measurement is commonly performed along with peroxide value to quantify secondary oxidation products?

• Iodine value
• Anisidine value
• Saponification value
• Acid value

Correct Answer: Anisidine value

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