Saponification value of an oil ,fat or of an ester is defined as the number of milligrams of potassium hydroxide(KOH) required to completely neutralize the free acids to saponify the esters present in 1gm of the substance.
i.e. to neutralize the fatty acid resulting from the complete hydrolysis of 1gm of the oil or fat.
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Significance of Saponification value
•The magnitude of saponification value gives an idea about the average molecular weight of the fat or oil.
•Higher the molecular weight of the fat , the smaller is its saponification value.
•Saponification Value also indicates the length of carbon chain of the acid present in that particular oil or fat.
•Higher the saponification value, greater is the percentage of the short chain acids present in the glycerides of the oil or fats.
Method of Analysis
•Take 2gm of substance under examination accurately into 200ml flask fitted with a reflux condenser.
Add 25 ml of 0.5M ethanolic KOH and a little pumic powder and boil under reflux on a water bath for 30min.
Add 1ml of phenolphthalein solution & titrate immediately with 0.5M HCL (Aml).
Carryout a blank titration omitting the substance under examination (Bml).
Calculate Saponification value as
W-weight of substance in gm
Note:- if oil has been saturated with carbon dioxide for perpose of preservation,gently reflux the solution of oil in ethanol(95%) and ether for 10min before titration
•the oil must be free from the carbon dioxide by exposing it in a swallow disc in a vaccum desiccator for 24 hrs before weighing the sample.
to determine saponification value of oils and fats.
•Fat solvent(1:1::ethanol:diethyl ether)
•Alcoholic KOH solution-0.5N(in 95% ethanol)
•Take 1g of fat/oil in abeaker and dissolved in about 3 ml of fat solvent(ethanol:ether )
•Quantitatively transferred the content of beater in round bottomed flask ,in the same beaker take7ml fat solvent more and transferred to flask twice.
•Add 25 ml of 0.5N alcoholic KOH solution ,mixed well and attached to reflux condenser
•Set up another reflux condenser as the blank with all other reagent present except the fat/oil.
•Place both the flaks on waterbath for 30 min then cooled the flask to room temp and added phenolphthalein indicator in both flasks and titrated with 0.5 N HCl.
•Note the end points, the difference between the blank and test reading used to calculate number of milligrams of 0.5 KOH required to saponify 1gm of fat.
Calculations of saponification value
Volume of KOH consumed by 1g fat=[Blank-Test]ml
1000ml of 1N KOH contains=56g of KOH
Aml of 0.5N KOH contains=56×A×0.5/1000 g KOH
=0.028A g KOH
Saponification value =mg of KOH consumed by 1g of fat
It cosist of substances present in oils and fats which are not saponifiable by alkali hydroxides and are determined by extraction with an organic solvent of a solution of the saponified substance under examination.
i.e. unsaponifiable matters are soluble in ordinary fat solvents.
Method of determination
•Take 5gm of substance under examination in 250ml flask with reflux condenser.
Add a solution of 2g of KOH in 40ml ethanol(95%) and heat on waterbath for 1hr with frequent shaking.
•Tranfer the substance in separately funnel already containing 100ml hot water,while the liquid is still warm shake very carefully with three quantities each of 100ml peroxide-free ether.
Combine the ether extract in second separating funnel containing 40ml of water,swirl gentely for few mins and allow to seperate and reject lower layer.
Now,wash the extract with two quantities each of 40ml of water and with 3 quantities each of 40ml of 3% w/v KOH each treatment being followed by washing with 40ml of water.
Finally wash the ether layer with successive quantities each of 40ml of water until the aqueous layer is not alkaline to phenolphthalein solution.
Transfer the ether layer to a weighed flask washing out separating funnel with peroxide-free ether.
Distill off ether and to the residue add 6ml of acetone.
Remove the solvent completely from flask with the aid of gentle current of air. And dried at 100-105℃ for 30min.
Cool in desiccator and weigh the residue & calculate the unspecified matter as percent w/w.
(Wt of Residue/wt of sample taken)×100
Dissolve the Residue in 20ml ethanol(95%) previously neutralised to phenolphthalein solution and titrate with 0.1m ethanolic KOH
If volume of 0.1M ethanolic KOH eceeds 0.2ml that amount weighed cannot be taken as unsaponifiable matter and test must be repeated