FIFTH EXPERIMENT: Lipids Properties

• Introduction:

These compounds are characterized as natural substances taht do not mix with water but dissolve in organic solvents.

Lipids are made in general of a long chains of hydrocarbons with relatively little oxygen.As a result of this, they tend to be non-polar, meaning they do not dissolve in polar solvents such as water.

• Materials:

1. Test tube rack.
2. 250ml beaker.
3. Water.
4. 6 test tube.
5. Cellulose paper.
6. Dropper.
7. Scissors.
8. Glass rod.
9. Olive oil.
10. Soap (detergent)
11. Milk with different fat content: Full-cream, semi-skimmed and skimmed milk.
12. Petroleum ether.
13. Ethanol.
14. Sudan III.

• Procedure:

Solubility of some lipids:

1. Clean and dry three test tube. Label as W (water), ethanol (E) and PE (ether)
2. Add 3 drops of oleic acid to 3 small test tubes.
3. Add 1 mL of water in teh first test tube (W).
4. Add 1 mL of ethanol in the second test tube (E).
5. Add 1 mL of petroleum ether in the third test tube (PE).
6. Shake carefully each test tube and record solubility and observations in your worksheet.

 

 

• Results:

The oil and ethanol don't dissol in water and ether can dissol in water.

Lipids identification:

      Translucent Mark:

1. Cut two pieces (10x10cm) of cellulose paper.
2. Put 1 drop of water in the first squared piece. You will see a transluced spot. Wait for a while and observe what is happening.
3. Put 1 Drop of olive oil in the second suqred piece of cellulose papaer. You will see a transluced spot. Wait for while and observe what is happening. Has the spot dissapered? Why?

• Results:

The oil is transluced because doesn't evaporate, water can evaporate.

Sudann III dye: Be careful Sudan red cxan stain clothes!

Sudan III is a red fat-soluble dye that is utilized in the identification of the presence of lipids, triglycerids and lipoproteins in liquids.

1. Take the W test tube of the first experiment and add 2 drops of Sudan III.
2. Prepare four test tubes: 3 with milk with different fat content (M1, M2, M3) and soda (S). Add two drops of Suddan III and observe the results.

• Results:

The proof of Sudan III doesn't work possibly because the solution was too diluted.

Permament emulsion:

1. Take a 250 mL beaker and put 100 mL water.
2. Add 1  mL of olive oil. With a glass rod stir the mixture vigorously and let it stand for a few minutes.
3. Make note of what is happening.
4. Add 2 drops of soap and stir the mixture again. Let it stand for a few minutes and notice the differences between both mixtures.

• Results:

The oil is translucent because it doesn't evaporate, however the water if it evaporates, leaving different stains.

• Questions:

1. From your observation, wich compunds can dissolev lipids? Ether
2. Do the oil and water mix? What can you conclude about the polarity of the oil if you know that water is polar? No, the oil non-polar.
3. Why is liquid the olive oil at room temperature? And why not the lard? Because is the faty acid insaturated. The lard is a faty acid saturated.
4. Why does the lipid leave a translucent spot on paper? Because the lipid does not evaporate.
5. Wich type of milk contains more lipids? Why? Milk full-cream, because they take away the semi-skimmed milk fats.
6. Did the oil and water mix when you added the soap?No, but a monolayer and a micelles separated oil from water formed.
7. What did the soap do to the fat? Separated in micelles.
8. Can you think about process and locations were compounds like the soap would be important to an animal? Acids biliars.