L7: LIPIDS PROPERTIES

1. INTRODUCTION

Lipids are heterogeneous group of compounds synthesized by organisms, that are present in all biological tissues. These compounds are characterized as natural substances that do not mix with water but dissolve in organic solvents, There are several classes of lipids including: fatty acids,waxes,tryacyglycerols, phospholipids,terpens and steroids. C,H and O are the principal elements of lipids althought oxygen content is reduced. Lipids are made in general of long chains of hydrocarbons with relatively little oxygen, they tend to be non-polar, meaning they do not dissolve in polar solvents such as water.


2. OBJECTIVES

- Test the solubility of lipids
- Identify lipids in liquids compounds.
- Understand what are an emulsion and the effect of detergents.


3. MATERIAL

- Test tube rack
- 250ml beaker
- Water
- 6 test tubes
- Cellulose paper
- Dropper
- Scissors
- Glass rod
- Olive oil
- Soap (detergent)
- Milk with different fat content
- Petroleum ether
- Ethanol
- Sudan III

4, PROCEDUCE 

- Solubility of some lipids:

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

- Lipids identificaion:

A) 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 translucednt spot. Wait for a while and observe what is happening,
3. Put 1 drop of olive oil in the second squared piece of cellulose paper. You will see a translucent spot,

B) Sudan III dye: Be careful red can stain clothes!!!

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

- Pemanent emulsion:

1. Take a 250ml beaker and put 100 ml of water.
2. Add 1ml of olive oil. With a glass rod stir the mixture vigorously and let it stand 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 diferences between both mixtures,

5. OBSERVATION

 We have been able to observe...

- In the first experiment we have tested that oil is insoluble in water and soluble in ether. In the second test tube the oil and ethanol didn't mix, the oil formed micelles.

- In the second experiment we tried to stain lipids with sudan III, unfortunatelly the dye didn't stain.

- In the last eperiment we tested that soap forms little micelles with oil, in a water solution. This mixture is called permanent emulsion.


6. QUESTIONS

1. From your observation, which compounds can dissolve lipids?

The ether can dissolve the 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?

The oil is not soluble in water and remains in the top of the solution.

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

Because the oil has a melting point much lower melting.

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

Because it contains lipids.

5. Which type of milk contains more lipids? Why?

Whole milk.

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

It produces a permanent ebulltion.

7. What did the soap do to the fat?

That can't join again.

8. Can you think about process and locations were compounds like the soap would be important to an animal?

Bile acids.