P7 LIPIDS PROPERTIES

OBJECTIVES

Test the solubility of lipids. Identify lipids in liquid compounds and understand what are an emulsion and the effect of detergents.

MATERIAL

·         Test tube rack

·         250 mL beaker

·         Water

·         6 test tubes.

·         Cellulose paper

·         Dropper

·         Scissors

·         Glass rod

·         Olive oil

·         Soap (detergent)

·         Milk with different fat content: full-cream, semi-skimmed and skimmed milk.

·         Soy juice

·         Petroleum ether

·         Ethanol

·         Sudan III

PROCEDURE

We have made four different experiments to identify lipids.

Solubility of lipids:

1. Clean and dry three test tubes. Write on the first: W (water); in the second: Ethanol (E); and in the third: PE (petroleum ether).
2. Add three drops of acid oleic to the three test tubes.
3. Add 1 ml of water in the tube W; add 1 ml of ethanol in the tube E and 1ml of petroleum ether in the PE.
4. Shake each test tube and record the solubility of each tube.

RESULTS:

WATER+OIL------- INSOLUBLE

ETER+OIL   --------- SOLUBLE

PE+ OIL------------ SOLUBLE

CONCLUSION: Lipids are insolubles in wàter but are soluble in apolar orgànic dissolvents.

Translucent mark:

1.  Cut to pieces (10cmx10cm) of cellulose paper.
2.  Put one drop of water in the first piece, you will see a translucent spot, wait and observe what is happening.
3.  Put one drop of olive oil in the other, you will see a translucent spot. Is that going to disappear, why?

 CONCLUSION: Fats will leave a glossy, oily residue when wiped on paper. When light falls upon paper, a part of it is transmitted, a part is scattered, a part is absorbed, and a part is reflected

Sudan III dye

1. Take the W test tub and add two drops of Sudan III.
2. Prepare four test tubes: 3 with milk, each of different fat content and the fourth with soy juice, observe the results.

RESULTS:

1-      SKIMMED MILK: The solution stain soft orange

2-      Semi-skimmed milk: The solution stain medium orange

3-      Whole milk: The solution stain reddish- Orange

4-      Soy juice: It doesn’t change the colour.

•          CONCLUSION: Sudan III is not soluble in water; it is, however, soluble in lipids. If lipids are present the Sudan III will stain them reddish-orange.

EMULSION

1.  Take the beaker of 250 mL and put 100mL of water.
2.  Add 1 mL of oil.
3.  With a glass rod stir the mixture and left it for 5 minutes. Observe what is happening.
4.  Add two drops of soap and then notice the different of both mixtures.

1. RESULTS:
   WATER AND OIL FORM A TEMPORARY EMULSION
   WATER , SOAP AND OIL FORM A PERMANENT EMULSION
   CONCLUSION:  SOAP IS A TENSOACTIVE THAT ELIMINATE THE SURFACE TENSION BETWEEN THE WATER MOLECULES, BY ONE HAND, AND THE SURFACE TENSION OF OIL. THEN THE MIXTURE IS HOMOGENEUS (PERMANENT EMULSION).