Iodine Number (Chemistry) Calculators

0 calculators tagged with “Iodine Number (Chemistry)”

The iodine number (iodine value, IV) is the mass of iodine (in grams) that reacts with 100 grams of a fat, oil, or other unsaturated compound — a direct measure of degree of unsaturation. Each carbon-carbon double bond (C=C) in a fatty acid reacts with one mole of I₂. The Wijs method uses iodine monochloride (ICl) in glacial acetic acid as the iodizing reagent, which is more reactive than I₂ alone. High iodine value (> 100) indicates highly unsaturated oils (linseed, sunflower); low values (< 20) indicate saturated fats (coconut oil, butter, lard). Iodine number is used in quality control of fats, oils, and industrial applications (drying oils for paints).

All Calculators

No calculators found for this topic.

Iodine Value Test

Standard method: Wijs reagent (ICl in glacial acetic acid) + fat sample → react for 30 min in dark. Add KI solution → ICl + KI → I₂ + KCl. Titrate excess I₂ with Na₂S₂O₃ (sodium thiosulfate) to starch endpoint. Iodine value = [(blank − sample) mL × N_Na₂S₂O₃ × 12.69] / sample mass (g). Where 12.69 = milliequivalent weight of I₂ × 1.269.

Typical Iodine Values

  • Linseed (flaxseed) oil: 170–204 (drying oil; polymerizes in air)
  • Sunflower oil: 120–145
  • Soybean oil: 117–141
  • Olive oil: 75–90 (mainly monounsaturated)
  • Palm oil: 44–58
  • Coconut oil: 6–11 (highly saturated)
  • Butter: 25–40
  • Lard: 45–75

Significance

Drying oils (IV > 130): cross-link and polymerize when exposed to O₂ → used in oil-based paints, varnishes, linoleum. Semi-drying oils (IV 100–130): partial drying properties. Non-drying oils (IV < 100): do not polymerize; used as lubricants and in food.

Glossary

Iodine Number (IV)
Grams of I₂ absorbed per 100 g of fat; each C=C double bond reacts with 1 mol I₂; linseed oil IV ≈ 180; olive oil ≈ 80; coconut oil ≈ 8; higher IV = more unsaturated.
Wijs Method
Standard iodine value test using ICl (iodine monochloride) in glacial acetic acid; excess ICl back-titrated with Na₂S₂O₃; AOCS Cd 1d-92 and ISO 3961 standards.
Drying Oil
Oil with IV > 130 that polymerizes when exposed to air oxygen; linseed (IV ≈ 180) and tung oil are classic drying oils; used in oil-based paints, varnishes, and linoleum.

Frequently Asked Questions

The iodine number (iodine value, IV) = grams of I₂ that react with 100 g of a fat or oil. Each C=C double bond in a fatty acid reacts with exactly one mole of I₂ (or ICl in the Wijs method). Therefore: IV directly measures the total number of double bonds per unit mass. Higher IV = more double bonds = more unsaturated fatty acids. A fat with IV = 150 has more than twice the unsaturation of a fat with IV = 70. Used to characterize: edible fats and oils quality control; classification as saturated (IV < 20), monounsaturated (IV 75–100), polyunsaturated (IV > 100); drying ability of industrial oils.

The Wijs method (AOCS Cd 1d-92; ISO 3961): (1) Weigh ~0.25–0.5 g of fat/oil into a glass-stoppered flask. (2) Add 20 mL Wijs reagent (ICl in glacial acetic acid). (3) Allow to react 30 min in the dark (protect from light — photocatalyzed decomposition would occur). (4) Add 20 mL 15% KI solution → reacts with excess ICl: ICl + KI → I₂ + KCl. (5) Add 100 mL water. (6) Titrate the liberated I₂ with standardized 0.1 M Na₂S₂O₃ to a pale yellow endpoint, then add starch indicator → titrate to colorless. (7) Run a blank (same procedure without fat). IV = (blank volume − sample volume) × N × 12.69 / sample mass.

Drying oils: IV > 130. These polymerize when exposed to air oxygen — a process called auto-oxidation followed by cross-linking. The polyunsaturated fatty acids (especially linolenic acid with 3 double bonds and linoleic acid with 2) in drying oils react with O₂ to form hydroperoxides → radical chain reactions → polymer network. Linseed oil (IV ≈ 180): rich in α-linolenic acid (C18:3) → fastest drying. Tung oil (IV ≈ 160): extremely fast drying. Applications: oil-based paints, varnishes, wood stains, linoleum, printing inks, artist oils. Semi-drying oils (IV 100–130): soybean, sunflower, corn — partial drying. Non-drying (IV < 100): olive, coconut, palm — don't polymerize; used in food and cosmetics.

Iodine value correlates directly with the proportion of unsaturated fatty acids: Each C=C double bond in one mole of fatty acid contributes 254 g/mol (1 mol I₂) to IV. For a pure fatty acid, IV = (number of double bonds × 253.8) / molar mass × 100. Stearic acid (C18:0): IV = 0 (no double bonds). Oleic acid (C18:1): theoretical IV = 253.8/282.5 × 100 = 89.9. Linoleic acid (C18:2): theoretical IV = 2 × 253.8/280.5 × 100 = 181. Actual oil IV = weighted average of fatty acid contributions. Example: sunflower oil is ~65% linoleic acid (C18:2) → high IV ≈ 130. Olive oil is ~72% oleic acid (C18:1) → lower IV ≈ 80.