L.7 LIPIDS PROPERTIES

INTRODUCTION:

Lipids are heterogeneous group of compounds synthesized by organisms that are present in all biological tissues. Lipids are made in general of 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. 

In this experiment we test the solubility of different oils and how to identify lipids from a sample, Our objectives where: 

- Test the solubility of lipids.

- Identify lipids in liquids compounds

- Understand what are an emulsion and the effect of detergents.

MATERIAL:

- Test tube rack
- 250mL beaker
- Water
- 6 test tubes- Cellulose paper
- Dropper
- Scissors
- Glass rod

- Olive oil
- Soap
- Milk: full-cream, semi-skimmed and skimmed milk.
- Petroleum ether
- Ethanol
- Sudan III

PROCEDURE:

Solubility of some lipids:

- Clean and dry 3 test tubes. Label as W (water), E (ethanol) and PE (ether).

- Add 3 drops of oleic acid to 3 small test tubes.

- Add 1mL of water in the first test tubes (W).

- Add 1mL of ethanol in the second test tube (E).

- Add 1mL of petroleum ether in the third test tube (PE).

- Shake carefully each test tube and record solubility and observations.

Lipids identification: 

Translucent mark:

- Take 2 pieces of cellulose paper.

- Put 1 drop of water in the first piece. You will see a translucent spot. Wait for a while and observe what is happening.

- Put 1 drop of olive oil in the second piece of cellulose paper. You will see a translucent spot. Wait for a while and observe what is happening.

Sudan III dye:

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

- Take the W test tube of the first experiment and add 2 drops of Sudan III. 

- Prepare four test tubes: 3 with milk with different fat content, and soda. Add to drops of Sudan III and observe the results. 

Permanent emulsion:

- Take 250 mL beaker and put 100mL of water.

- Add 1 mL of olive oil. With a glass rod stir the mixture vigorously and let it stand for a few minutes.

- Make note of what is happening. 

- 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 AND CONCLUSIONS:

- Lipids are insoluble in water and soluble in ether (organic compound). In the second test tube, the oil and ethanol didn't mix because the oil formed micelles.
- Sudan III stains lipids, but in our experiment didn't work.
- Lipids leave a translucent spot in cellulose paper. 

QUESTIONS:

1.- From your observation, wich compounds can dissolve lipids? 

Ether can dissolve lipids. 

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 is insoluble in water, the oil is non-polar. 

3.- Why is liquid the olive oil at room temperature? And why not the lard?

Oil is the fat acid insaturated. Because the lard is a fat acid saturated.

4.- Why does the lipid leave a translucent spot on paper? 

Because the lipid don't evaporate.

5.- Wich type of milk contains more lipids? Why?

 Full-cream milk, because they take away the semi-skimmed milk fats. Contain all the lipids.

6.- Did the oil and water mix when you added the soap?

No, it forms micelles that can separated oil from water. 

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? 

Bile acids.