Characterization of Lipids Activity 5A

At the end of this activity, the students are expected to:

A. Name the components of the lipids,B. describe the characteristics of lipids, andC. Discuss the principle in each of the tests

employed for lipids.

Objectives:

Determine solubility of one drop of coconut oil in 1 ml of the ff. solvents: water, dilute HCl, dilute NaOH, cold alcohol, hot alcohol, chloroform, and ether.

A. Solubility

Lipids are non-polar organic compounds. The physical properties of fatty acids, and of compounds that contain them are largely determined by the length and degree of unsaturation of the hydro carbon chain. The nonpolar hydrocarbon chain accounts for the poor solubility of fatty acids in water. Solubility of a substance depends on a simple rule of thumb “like dissolves like” this statement indicates that a solute will dissolve best in a solvent that has a similar chemical structure to itself. The overall solvation capacity of a solvent depends primarily on its polarity.

Explain the solubility of the different kinds of lipids in each solvent used.

Water- Coconut oil is insoluble in water even at room temp. since water is a polar solvent it will not dissolve coconut oil which is nonpolar.

Dilute HCl- Coconut oil is insoluble in dilute acid (dilute HCl) even if HCl is a nonpolar inorganic solvent. Coconut oil has higher molecular weight and when dissolved in dilute acid, it tends to float.

Dilute NaOH- Coconut oil is insoluble in dilute alkali (dilute NaOH). In the solution the coconut oil it tends to form as a white colloidal matter after the addition of dilute alkali.

Ethyl alcohol- Like water ethyl alcohol is a polar solvent and will not dissolve most nonpolar solutes as oil.

Chloroform- Coconut oil is soluble in chloroform. Oil is a nonpolar organic compound same as chloroform.

Ether- Coconut oil is soluble in ether since ether is an organic nonpolar solvent.

1. Place one drop of the following oils separately on a piece of bond paper (preferably substance 16). Make sure the drops are placed apart from each other.

a. Coconut oilb. Linseed oilc. Peanut oild. Cod liver oile. Olive oilf. Corn oil

B. Formation of Translucent Spot

Formation of Translucent Spot

FORMATION OF TRANSLUCENT SPOT

Lipids have a characteristic greasy feel

When brought in contact with a substance like paper, it penetrate through it producing a translucent spot

Fats are non-volatile

The spot of grease can never absorb enough heat to vaporize

When the liquid is inside the sheet of paper, it diffracts light – TRANSLUCENT PHENOMENON

Based on our test results, it shows that peanut oil evaporated 1st, followed by coconut oil, corn oil, cod liver oil and lastly linseed oil. It is stated that the difference in molecular weight and number of double bonds affect the rate of evaporation of oil. The longer the fatty acyl chain and the fewer the double bonds the lower the evaporation rate. In our test the rate of evaporation was also affected by the quantity of oil dropped in the paper.

Coconut oil

Linseed oil

Peanut oil

Cod liver oil Corn oil

Olive Oil

Each lipid is different with each other, especially with the number and branching of their carbon chain, the longer the chain and the more it is branching the longer the time it evaporates. There is also a factor in the degree of unsaturation of the lipid. Saturated fatty acids or saturated fats tend to evaporate a lot longer than unsaturated fat. Saturated fats are composed of many single carbon bonds that make the substance less volatile. Unsaturated fats are composed of one or more double bonds. The double bonds make the fat more volatile. In other words there are differences in the evaporation of different kind of oil because their evaporation rate mainly depends upon their structural formula. The differences in molecular weight and number of double bonds therefore affect the rate of evaporation of oil.

Explain why other oils evaporate faster, others do not. Give the structural formula of these oils.

In the test there was no change in the color of litmus paper (Litmus paper blue and red). Theoretically the oil should turn into acidic since it was exposed to an open environment and thus undergo Rancidity. The result was maybe due to several factors like the oil used was not fresh.

C. Reaction of Fats

In the experiment the oil give a positive result since coconut oil is a lipid and is composed of glycerol.

Heat

Oil or fat Glycerol + Fatty acid

CH2OH CH2

CHOH KHSO4

Heat CH + 2H2OCH2OH (Glycerol ) CHO (Acrolein)

D. Acrolein Test