pHYSICAL cHEMISTRY - Iv

Experiment 1

Principle

Fats and oils are the principle stored forms of energy in many organisms. They are highly reduced compounds and are derivatives of fatty acids. Fatty acids are carboxylic acids with hydrocarbon chains of 4 to 36 carbons, they can be saturated or unsaturated. The simplest lipids constructed from fatty acids are triacylglycerols or triglycerides. Triacylglycerols are composed of three fatty acids each in ester linkage with a single glycerol. Since the polar hydroxyls of glycerol and the polar carboxylates of the fatty acids are bound in ester linkages, triacyl glycerols are non polar, hydrophobic molecules, which are insoluble in water.

Saponification is the hydrolysis of fats or oils under basic conditions to afford glycerol and the salt of the corresponding fatty acid. Saponification literally means "soap making". It is important to the industrial user to know the amount of free fatty acid present, since this determines in large measure the refining loss. The amount of free fatty acid is estimated by determining the quantity of alkali that must be added to the fat to render it neutral. This is done by warming a known amount of the fat with strong aqueous caustic soda solution, which converts the free fatty acid into soap. This soap is then removed and the amount of fat remaining is then determined. The loss is estimated by subtracting this amount from the amount of fat originally taken for the test.

Materials required

Apparatus:

Conical Flask,100ml beaker, Weigh Balance, Dropper, Reflux condenser, Boiling Water bath, Glass pipette (25ml), Burette

Chemicals: Fats and Oils [coconut oil, sunflower oil], Potassium hydroxide [0.5N], Hydrochloric acid[0.5N], Phenolphthalein indicator.

Procedure

About 1 g of the given oil or fat is taken in a conical flask but weighed accurately (w g).The oil/ fat is dissolved in 25 mL of 0.5 N alcoholic potassium-hydroxide solution.Then the reaction mixture is refluxed using a water condenser on a water bath for half an hour.The resulting solution is cooled and titrated against a 0.5 N HCl solution adding 1 mL of phenolphthalein.The number of mL of acid required is noted (a).An exactly identical blank experiment is performed.Number of mL of HCl required is noted (b).

Saponification value or number of fat = mg of KOH consumed by 1g of fat.

Weight of KOH = Normality of KOH * Equivalent weight* volume of KOH in litres

Volume of KOH consumed by 1g fat = [ Blank(b) – test(a) ] ml

Observation table

Calculations

Saponification Value = (b - a ) * N * 56.1 / w

Where, (b-a) = Vol.of Acid required to neutralise remaining KOH used in mL (Blank reading - Sample reading

N= Normality of KOH

w= weight of sample taken in gram

here, 56.1 is the Equivalent wt. of KOH

Significance:

1.The magnitute of saponification value gives an idea about the average molecular weight of the fat or oil.

2.Higher the molecular weight of the fat, the smaller is its saponification value

3.Saponification value also indicates the length of carbon chain of the acid present in that particular oil or fat.

4.Higher the saponification value,greater is the percentage of the short chain acids present in the glycerides of the oil or fats.

Result

Saponification value of the given oil /fat is ___________

Conclusion

Saponification value of given sample oil is obtained as per Table.

Reference Material

1. An Introduction to Practical Biochemistry, third edition by David T Plummer, McGraw-Hill, c. McGraw-Hill Book Company (U.K.) Ltd., London. 1987.

2. Lehninger Principles of Biochemistry, Fifth Edition by David L. Nelson and Michael M Cox.

3. “Experimental Biochemistry “, Beedu sashidhar rao, Vijay Deshpande, I K International Pvt.ltd; ISBN 81-88237-41-8.

4. Jayaraman J; Laboratory Manual in Biochemistry, Wiley Eastern Limited. 2.

5. JIS K 0070-1992 Test Method for Acidity, Saponification value, Ester value, Iodine value and Hydroxy value of Chemical products and Unsaponifiables.

6. Advanced Practical Organic Chemistry by O.P. Agarwal.

Questions

1.What is Saponification Value?

2. What type of reaction saponification?