Theory & Procedure, Qualitative Analysis of Oils & Fats | Additional Study Material for NEET PDF Download

Our Objective

Our objective is to study some simple tests of oils and fats.

The Theory

What are Fats and Oils?

Fats and oils are concerted source of energy. Certain percentage of body weight of human being is fat and 20-35% of calories should come from fat. Fats in the diet are essential for good health and are needed for the growth of the body and the processing of vitamins. They make up part of all cells and help to maintain the body temperature. They form fatty tissue around delicate organs to protect them from injury.

Chemically fats and oils are triesters of glycerol and higher fatty acids. They are of animal or plant origin. Desi ghee is animal ghee while vanaspati ghee is vegetable ghee. Fats are solids while oils are liquids at ordinary temperature. Fats and oils may be saturated or unsaturated.

Saturated fat

Saturated fats contain only single bonds within the carbon chain. Saturated fats are of animal origin and are usually present in solid form. It increases the blood cholesterol level. Some examples are meat fat, butter etc. Coconut oil and palm oil also contain saturated fat.

Unsaturated fat

Unsaturated fats contain double bonds within the carbon chain. Unsaturated fat is found in fish like salmon and tuna, nuts, seeds etc.

Some Important Tests for the Detection of Oils and Fats

Solubility test

Oils and fats are soluble in organic solvents like, chloroform, alcohol etc. but are insoluble in water.

Translucent Spot test

Fats and oils have higher boiling points so at room temperature they cannot absorb enough heat to evaporate. When fat or oil is place on a sheet of paper, it diffracts light. The diffracted light can pass from one side of the paper to another side and produces a translucent spot.

Acrolein test

Acrolein test is used to detect the presence of glycerol or fat. When fat is treated strongly in the presence of a dehydrating agent like potassium bisulphate (KHSO₄), the glycerol portion of the molecule is dehydrated to form an unsaturated aldehyde, acrolein that has a pungent irritating odour.

Baudouin test

This test is used to detect the presence of seasame oil. Seasame oil gives a characteristic rose red colour with concentrated hydrochloric acid and furfural solution. Vanaspati ghee contains 5% seasame oil while pure desi ghee does not contain seasame oil. So this test can be applied to find out whether the given sample of desi ghee contains vanaspati ghee or not.

Huble's test

This test is used to detect the degree of unsaturation in oil or fat. Huble’s reagent reacts with alcoholic solution of iodine that contains some mercuric chloride. During the reaction, the violet colour of iodine fades away if the oil or fat is unsaturated. If the oil or fat is saturated, the violet colour of iodine does not fade away.

Learning Outcome

• Students understand various identification tests for oils and fats.
• Students acquire the skill to identify saturated and unsaturated fat.
• Students acquire skill to perform the experiment in the real lab.

Materials Required

Samples

• Desi ghee
• Vanaspati ghee
• Refined oil- Cotton seed oil & Linseed oil

Reagents

• Water
• Alcohol
• Chloroform
• Potassium bisulphate (KHSO₄) crystals
• Conc. HCl
• 2% furfural solution in alcohol
• Huble’s reagent

Apparatus

• Test tube
• Dropper
• Filter paper

Procedure

Real Lab Procedure

Solubility test

Shake a small amount of the given sample with 5 ml each of water, alcohol and chloroform in three test tubes.

Observation and Inference

Transluscent Spot test

Place a little of the substance on a filter paper and press it on the folds of the filter paper and unfold the filter paper.

Observation

Inference

On unfolding the filter paper, the appearance of transluscent spot on the filter paper indicates the presence of oil or fat.

Acrolein test

Heat a little of the sample with some crystals of potassium bisulphate in a test tube.

Observation

Inference

A pungent irritating odour of acrolein confirms the presence of oil or fat.

Baudouin test

Take 5 ml of melted ghee in a test tube and add 5 ml of conc. HCl and 2-3 drops of 2% furfural solution in alcohol in it. Shake the test tube well. Keep it aside for 5-10 minutes.

Observation

Inference

Rose-red colour is formed due to the presence of seasame oil. Thus vanaspati ghee contains seasame oil whereas pure desi ghee does not contain seasame oil. So this test is used to distinguish between desi ghee and vanaspati ghee.

Huble’s test

Take two test tubes and label them as I and II. Put 3ml of chloroform into each test tube. Then add 3-4 drops of cotton seed oil into test tube I and linseed oil in test tube II. Shake the test tubes well and add 3 drops of Huble’s reagent in each test tube and observe the fading of violet colour in the test tubes.

Observation

Inference

The violet colour of iodine fades away in test tube II, while, violet colour in test tube I does not fade away indicating that linseed oil is more unsaturated than cotton seed oil.

Simulator Procedure (as performed through the Online Labs)

You can select the test from ‘Select the test’ drop down list.

Solubility Test

You can select the solvent from ‘Select the solvent’ drop down list.

Water

• Drag the dropper to the test tube containing desi ghee to drop water into it.
• Drag the test tube to shake the contents of the test tube.
• Drag the dropper to the test tube containing vegetable ghee to drop water into it.
• Drag the test tube to shake the contents of the test tube.
• Drag the dropper to the test tube containing refined oil to drop water into it.
• Drag the test tube to shake the contents of the test tube.
• Click on the inference icon to see the inference.

Alcohol

• Drag the dropper to the test tube containing desi ghee to drop alcohol into it.
• Click on the knob of the burner to turn it on.
• Drag the test tube containing desi ghee to the burner to heat the contents of the test tube.
• Drag the dropper to the test tube containing vegetable ghee to drop alcohol into it.
• Click on the knob of the burner to turn it on.
• Drag the test tube containing vegetable ghee to the burner to heat the contents of the test tube.
• Drag the dropper to the test tube containing refined oil to drop alcohol into it.
• Click on the knob of the burner to turn it on.
• Drag the test tube containing refined oil to the burner to heat the contents of the test tube.
• Click on the inference icon to see the inference.

Chloroform

• Drag the dropper to the test tube containing desi ghee to drop chloroform into it.
• Drag the test tube to shake the contents of the test tube.
• Drag the dropper to the test tube containing vegetable ghee to drop chloroform into it.
• Drag the test tube to shake the contents of the test tube.
• Drag the dropper to the test tube containing refined oil to drop chloroform into it.
• Drag the test tube to shake the contents of the test tube.
• Click on the inference icon to see the inference.

Translucent Spot Test

You can select the sample from ‘Select the sample’ drop down list.

Desi Ghee

• Drag the dropper to the first filter paper to drop desi ghee into it.
• Drag the second filter paper towards the filter paper containing the sample to press the sample with it.
• Drag the filter paper towards the lighting candle.
• Move the filter paper over the flame, the light will be visible only through the spot formed by the ghee.
• Click on the inference icon to see the inference.

Vanaspati Ghee

• Drag the dropper to the first filter paper to drop vanaspati ghee into it.
• Drag the second filter paper towards the filter paper containing the sample to press the sample with it.
• Drag the filter paper towards the lighting candle.
• Move the filter paper over the flame, the light will be visible only through the spot formed by the ghee.
• Click on the inference icon to see the inference.

Refined Oil

• Drag the dropper to the first filter paper to drop refined oil into it.
• Drag the second filter paper towards the filter paper containing the sample to press the sample with it.
• Drag the filter paper towards the lighting candle.
• Move the filter paper over the flame, the light will be visible only through the spot formed by the oil.
• Click on the inference icon to see the inference.

Acrolein Test

You can select the sample from ‘Select the sample’ drop down list.

Desi Ghee

• Drag the spatula to the test tube to put potassium bisulphate crystals into desi ghee.
• Click on the knob of the burner to turn it on.
• Drag the test tube to the burner to heat the contents of the test tube.
• Click on the inference icon to see the inference.

Vanaspati Ghee

• Drag the spatula to the test tube to put potassium bisulphate crystals into vanaspati ghee.
• Click on the knob of the burner to turn it on.
• Drag the test tube to the burner to heat the contents of the test tube.
• Click on the inference icon to see the inference.

Refined Oil

• Drag the spatula to the test tube to put potassium bisulphate crystals into refined oil.
• Click on the knob of the burner to turn it on.
• Drag the test tube to the burner to heat the contents of the test tube.
• Click on the inference icon to see the inference.

Baudouin Test

• Drag the dropper to the test tubes to drop Conc. HCl into desi ghee and vanaspati ghee respectively.
• Drag the dropper to the test tubes to drop 2% furfural solution in alcohol into desi ghee and vanaspati ghee respectively.
• Wait for some time to complete the reaction.
• Click on the inference icon to see the inference.

Hubble's Test

• Drag the dropper to the test tube containing cotton seed oil to drop chloroform into it.
• Drag the test tube to shake the contents of the test tube.
• Drag the dropper to the test tube containing cotton seed oil to drop Hubble's reagent into it.
• Drag the dropper to the test tube containing linseed oil to drop chloroform into it.
• Drag the test tube to shake the contents of the test tube.
• Drag the dropper to the test tube containing linseed oil to drop Hubble's reagent into it.
• Click on the inference icon to see the inference.

To redo the experiment, click on the ‘Reset’ button.

Note: Click on the ‘HELP’ button to see the instructions.

Precautions

• Handle the chemicals with care.
• Use lab coats and gloves while performing the experiment.
• Use droppers to take the reagents.