Lipid Recognition and Saponification Lab Procedures

Recognition of Lipids

Laboratory Materials

• Test tubes
• Rack
• Glass rods
• Lighter
• Beakers
• Pipettes
• 20% NaOH solution
• Sudan III solution
• Red ink
• Ether, chloroform, or acetone
• Olive oil

2.1 Saponification

Basis

Hot fat reacts with sodium or potassium hydroxide, decomposing into two elements: glycerol and fatty acids. These ions combine with the hydroxide to produce soaps, which are sodium or potassium salts of fatty acids. In living organisms, the hydrolysis of triglycerides is facilitated by specific enzymes called lipases, which form fatty acids and glycerol.

Technique

1. Place 2ml of oil and 2ml of 20% NaOH in a test tube.
2. Shake vigorously and place the tube in a water bath for 20 to 30 minutes.
3. Afterward, three phases will be visible in the tube: a clear bottom layer containing the leftover soda solution and the glycerol formed, an intermediate semi-solid soap layer, and an upper layer of unchanged lipid.

2.2 Lipid Staining

Basis

Lipids are stained selectively with the orange-red dye Sudan III.

Technique

1. Arrange two test tubes on a rack and add 2ml of oil to each.
2. Add 4-5 drops of an alcoholic solution of Sudan III to the first tube.
3. Add 4-5 drops of red ink to the second tube.
4. Shake both tubes and wait.
5. Observe the results: In the Sudan III tube, all the oil should appear stained. In the ink tube, the ink will settle at the bottom, and the oil will remain unstained.

2.3 Solubility

Basis

Lipids are insoluble in water. When shaken strongly, the lipid divides into droplets, forming a transient milky emulsion. This emulsion disappears at rest as the fat droplets coalesce into a layer that sits on top of the water due to its lower density. Conversely, fats are soluble in organic solvents such as ether, chloroform, acetone, or benzene.

Technique

1. Place 2ml of oil into two separate test tubes.
2. Add 2ml of water to the first tube and 2ml of ether (or another organic solvent) to the second.
3. Shake both tubes vigorously and let them stand.
4. Observe the results: The oil dissolves in the ether, whereas in the water tube, the oil separates and rises due to its lower density.

Review Questions

1. What are soaps?
2. How is soap produced?
3. Why does glycerol appear in the aqueous phase during saponification?
4. Which enzyme in the digestive system achieves the hydrolysis of fats?
5. Describe the reaction of the Sudan III-oil mixture versus the oil-ink mixture and explain the difference between the two results.
6. What happens to a water-in-oil emulsion after a few minutes of rest? What happens with benzene and oil? Why do these differences occur?

Experimental Results