L7. Lipids properties

On december 1st we did a new interesting experiment related with lipids. These compounds are characterized as natural substances that do not mix with water but dissolve in organic solvents, C, H and O are the principal elements of lipids. The objectives of this experiments are to test the solubility of lipids, indetify lipids in liquids compunds and to understand what is an emulsion and the effect of detergents. We can divide this experiment in three.

MATERIALS

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

-Olive oil
-Soap
-Milk with different fat content (full-cream, semi-skimmed, and skimmed milk)
-Petroleum ether
-Ethanol
-Sudan III

SOLUBILITY OF SOME LIPIDS
PROCEDURE

 1-First we cleaned and dried three test tubes, we labeled them as W (water), E (ethanol, and PE (ether).
2- Then we added 3 drops of oleic acid to the three test tubes.
3- We added 1 ml of water in the first test tube (W).
4- 1 ml of ethanol in the second test tube (E).
5- 1ml of petroleum ether in the thirs test tube (PE).
6- Finally we shaked each test tube and recorded solubility and observations in our worksheet.

Results and observations: We saw that in the test tube W the oleic acid didn't dissolve, in the E test tube micelles had formed and in the last PE test tube it dissolved completely because ether is an organic dissolvent.

LIPIDS IDENTIFICATION:
A. TRANLUSCENT MARK:

1- Our teacher gave us two pieces of cellulose paper.
2- In the first paper we put one drop of water, we saw a translucent spot and then we waited a little bit to see what was happening.
3- Then we put a drop of olive oil on the second piece of cellulose paper and we saw a translucent spor also. We waited to see what was happening.
4- Finally we wrote the results in our worksheet.

Results and observations:  The drop of water of the first piece of paper dried after a while and didn't leave any marks but the drop of oil was still visible when dried, it was translucid.

B. SUDAN III dye

1-We took the W test tube of the first experiment and added 2 drops of Sudan III.
2- Then we prepared three test tubes with full-cream, semi-skimmed and skimmed milk and also put 2 drops of Sudan III in each test tube to stain it.

Results and observations: The water had to turn black if there were fatty acid in the solution but in our experiment it didn't work and nothing happened.

PERMANENT EMULSION:

1- We took a 250 ml beaker and put 100 ml of water there.
2- Then we added 1 ml of olive oil and with a glass rodd we stirred the mixture vigorously and let it stand for a few minutes.
3- After taking note of what was happening we added 2 drops of soap and stirred the mixture again, and waited for a little bit to notice the difference.

Results and observations: First when we added oil to the water a layer of oil formed in the top part of the water. When we added soap microdrops appeared, little micelles. Soap doesn't dissolve the lipid, it just wraps it so the oil layer can't be formed.

QUESTIONS:
1-From your observations, which compunds can dissolve lipids?
Organic solvents can dissolve lipids, for example in our case ether dissolved them.

2-Do the oil and water mix? No
What can you conclude about the polarity of oil if you know water is polar?
I can say that lipids tend to be non-polar because they are made of longs chains of hydrocarbons with relatively little oxygen (hydrocabron chain), and this fatty acid tail is hydrophobic.Water molecules are strongly attracted to each other, this is the same for oil, because they are more attracted to their own molecules they just don't mix together. They separate and the oil floats above the water because it has a lower density.

3- Why is olive oil liquid at room temperature? And why not the lard?
Olive oil is liquid at room temperature because it is unsarurated (the chain bends and it only bonds on one part, it's easier to break). Lard isn't liquid because it's saturated (so it's harder to break the bonds)

4-Why does a lipid leave a translucent spot on paper?
In their liquid state oils and fats easily penetrate into the pores of dry substances. The lipids soak into the paper fibres, but the lipid spot evaporates much more slowly than water (because the forces that hold the lipid molecules together are stronger than those in water molecules)

5-  Which type of milk contains more lipids? Why?
The full-cream milk contains more lipids because it has more fat (fatty acids).

6- Did the oil and water mix when you added soap? 
Yes. Detergent is attracted to both water and oil helping them all join together and form something called an emulsion.

7-What did the soap do to the fat? 
Soap on one end it is hydrophillic (that is polar) and on the other end it is hydrophobic (non polar). So, the polar end of the soap molecule will attract the water molecules while the non-polar end of the molecule attracts the oil molecules.
Soap doesn't dissolve the lipid, it just wraps it so the oil layer can't be formed.

8- Can you think about process and locations were compounds like the soap would be important to an animal? 
Soap makes insoluble particles become soluble which allows water to rinse the particles away. This means that while oil doesn’t naturally mix with water, soap can suspend oil/dirt in such a way that it can be removed. They are useful in bile acids.