Exercise C Saturated Or Unsaturated You Be The Judge

  1. The Sudan IV dye (powder is soluble in lipids only. The more red color, the greater percentage of lipids arc present in the substance being tested. The dye will nor dissolve in substances that are not composed of lipids.
  2. It will take about a week to sec the results of the experiment on drying oils. Some good drying (polyunsaturated) oils arc linseed, walnut, safflowcr, tung, and poppy seed. These can be purchased from an art supply store or a hobby store. Oils that w ill nor dry (monounsaturatcd) include peanut, canola, and olive. Corn oil is intermediate in drying time.

Linseed oil (high degree ofpolyunsaturation) dries in about 3 days. Cottonseed, walnut, safflowcr, pop-pvsced and sunflower oil w ere tacky after a week's exposure to the air; although polyunsaturated, they have fewer double bonds than linseed oil. Olive and peanut oils (monounsat uratcd oils) did not dry in a w eek's rime.

3. Oils that arc highly polyunsaturated absorb the iodine more quickly (thus becoming colorless). Sunflower oil takes about 2-3 hours to become completely col orlcss but is noticeably lighter in about an hour. Pop pyseed and sunflower oils also become colorlcss in about the same time.

Oils that arc have a lower degree of unsaruration and do nor absorb the iodine and hencc do not change color as quickly arc olive, peanut, and canola. Corn was intermediate in clearing time. Have student teams pick two different oils and then compare class results at the end of the laboratory period. Use l2KI as the iodine solution for this test. To prepare I2KI, dissolve 20 g KI (potassium iodide) in 1.000 ml distilled water. Using a magnetic stirrer, add 4.0 g of iodine to the potassium iodide solution. It will take some time for the iodine to dissolve. Store in brow n bottles as I:KI breaks down in light. Dispense in dropper bottles.

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