Bromine Water Test 5f216

BROMINE WATER TEST By: Anne Marielle D. Manalo

Objective: To test for the presence of unsaturation in a fatty acid or a triglyceride.

Results: Sample

Result

Vegetable Oil

Colorless

Lecithin

Colorless

Principle: The presence of unsaturation in a fatty acid or a triacylglycerol can be detected by reaction with bromine. If the orange color of a bromine solution added to a lipid fades quickly, an addition reaction has occurred and the oil or fat is unsaturated.

Type Equation Used:

Sample Equation Involved: Vegetable Oil:

+ (orange) Br 2 (colorless)

Sample Equation Involved: Lecithin:

+ (orange) Br 2

(colorless)

Explanation of Results: Why does vegetable oil showed positive results? Vegetable oil is a triglyceride extracted from a plant and is liquid in room temperature. It contains double carbon-carbon bonds making it unsaturated. Bromine readily add up at the double bonds, and a colored solution of bromine when absorbed and decolorized in the presence of a lipid, indicates the presence of double bond. The more double bonds there are, the

Explanation of Results: Why does lecithin showed positive Lecithin is aresults? generic term to designate any group of yellow-brownish fatty substances occurring in animal and plant tissues. Bromine readily add up at the double bond of the unsaturated fatty acid, and a colored solution of bromine when absorbed and decolorized in the presence of a lipid, indicates the presence of double bond.

ACROLEIN TEST

Objective: To test for the presence of glycerol.

Procedure: 1. Prepare 3 clean and dry test tubes

1st test tube: Add a drop of glycerol.

2nd test tube: Add a drop of cooking oil

3rd test tube: Add a drop of lecithin from the soft gel capsule.

Procedure: 2. Mix a pinch-sized amount of powdered potassium bisulfate to all the tubes.

Procedure: 3. Heat the mixture gently over a small flame. Note the odor of the vapor and record observations.

Results:

SAMPLE

ODOR

Glycerol

Burnt smell

Cooking oil

Burnt smell

Lecithin

Burnt smell

Principle: When a fat is heated strongly in the presence of a dehydrating agent such as potassium bisulfate (KHSO), the glycerol portion of the molecule is dehydrated to form the unsaturated aldehyde, acrolein (CH2=CH–CHO), which has the peculiar odor of burnt grease.

Sample Equation Involved: a. Glycerol and Potassium bisulfate

Sample Equations Involved: b. Vegetable oil and Potassium bisulfate H+ + 3H2O

KHSO 4

glycerol

+

Sample Equation Involved: c. Lecithin and Potassium bisulfate

What is the compound responsible for your observation? The heat-induced dehydration

of glycerol is the one responsible for the release of acrolein. Acrolein is the compound responsible for the burnt smell.

What is the purpose of the potassium bisulfate used? When lipids are heated in the presence of a dehydrating

agent

such

as

potassium

bisulfate (KHSO4), the glycerol portion of the molecule

is

dehydrated

to

unsaturated aldehyde, acrolein.

form

the

What group of lipids was identified by this test?

Glycerides was the group of lipids identified by this test.