EXPERIMENT 7 DETERMINATION OF SAPONIFICATION VALUE
Stmcture
7.1 Introduction Objective
7.2 Experiment 7.2.I Principle 7.2.2 Requirements 7.2.3 Procedure 7.2.4 Observation 7.2.5 Calculations 7.2.6 Results
7.3 Precautions
7.1 INTRODUCTION
The saponification value of an oil or fat (lipids) is defined as the number of mg of potassium hydroxide required to neutralize the fatty acids resulting from the complete hydrolysis of 1 g of the sample. A soap is formed during the saponification, for example:
C3H5(CI7H35COO)3+ 3KOH = C3H5(OH) 3 + 3 CI7H35·COOK Stearin Glycerol Potassium stearate The esters of the fatty acids oflow molecular weight require the more alkali for saponification, so that the saponification value is inversely proportional to the mean of the molecular weights of the fatty acids in the glycerides present. As many oils have somewhat similar values (e.g. those in the olive oil series fall within the range 188-196), the saponification value is not, in general, as useful for identification purposes as the iodine value. The saponification value is of most use for detecting the presence of coconut oil (SV 255), palm-kernel oil (SV 247) and butterfat (SV 225), which contain a high proportion of the lower fatty acids. The presence of paraffin hydrocarbons may be detected as cloudiness when water is added to the ethanolic saponified oil or fat solution.
Objective
After studying and performing this experiment you should be able to: • determine the saponification value of oil.
7.2 EXPERIMENT
7.2.1 Principle
When a fat is boiled with an excess of alcoholic potassium hydroxide (KOH), the triglycerides hydrolyse, and glycerol and soap are formed. The alkali consumed by 25 Practical Manual for Pulses this hydrolysis is a measure of the Saponification Value (S.v.). It is defined as the and Oilseeds number of milligrams of potassium hydroxide (KOH) required to saponify completely one gram of the oil or fat. 7.2.2 Requirements
0 100 g Potassium hydroxide ii) 100 ml aldehyde free alcohol
iiD Hydrochloric acid (0.5 N) iv) Pipette 25 ml v) Conical flask 250 ml vi) Few pieces of pumice vii) 5 ml of phenolphthalein ( 1per cent) viii) Burette 7.2.3 Procedure
Melt the sample, ifnot already in liquid form, and filter. Ensure that the sample is free of impurities and moisture. Weigh I to 2 g. of the sample into a 250 ml conical flask having a ground glass joint. Pipette 25 ml of alcoholic KOH solution and add a few glass beads or pieces of pumice. Connect the flask to an air condenser at least 65 cm (or preferably 202 cm) long. Reflux the sample on a water bath or a hot plate for not more than 1hour. Boil gently but steadily until the sample is completely saponified as indicated by the absence of any oily matter and appearance of clear solution. Allow the flask and condenser to cool. Wash the inside of the condenser with about 10 ml of hot ethyl alcohol neutral to phenolphthalein. Add I ml of phenolphthalein indicator and titrate with standard HCI. Conduct a blank determination alongside. When testing samples which give dark coloured soap solution, the observation of the end point of the titration may be facilitated either by using (i) thymophthalein or alkali blue 6 B inplace of phenolphthalein, or (ii) an indicator containing 1rnl of a 0.1% (w/v) solution of methylene blue in water to reach 100 ml of phenolphthalein (mixed before titration). 7.2.4 Observation
S. No Weight of Blank titre Sample titre sample (g) value (b) value (a)
7.2.5 Calculations
.. . (b-a) x28.05 Saponifiaction Value of 011 (S.Y.) = Wt f I ( ) .0 samp e g
Method made used for measuring unsaturation are determination of iodine value and thiocyanogen value. These methods are based on the addition of halogen and 26 thiocyanogen respectively at double bonds. 7.2.6 Results Determination of Saponification Value The sponification value of the oil (name ofthe oil) is .
7.3 PRECAUTIONS i) Please ensure that all glassware like is Pipette, Burette, Conical flask etc. are clean and free of any impurities. ii) Carry out the titration most accurately.
27