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11 Feb 2009 23:37:10 IST

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what is saponification value and its relation with molecular wt

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what is saponification value and its relation with molecular wt

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Madhusudan Chavan

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13 Feb 2009 18:43:51 IST

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Saponification value is defined as the number of miligrams of potassium hydroxide required to completely saponify one gram of oil or fat.

saponification value id determined by refluxing a weighed quantity (1-2g) of the fat or oil with a known excess of standard potassium hydroxide solution and then titrating the unreacted alkali against a standard acid. For example, saponification value of trilaureate or tripalmitin can be determined as follows :

H23C11COOCH2-CH(O-COC11H23)-CH2-O-COC11H23 + 3 KOH ......> 3C11H23COOK + CH2OHCHOHCH2OH

Trilaureate ( mol. wt.638) 3x56 soap glycerol

From the above equation, one mole of fat = three moles of KOH

or 638 g of fat = 3x56 g= 3x56x1000 mg of KOH

Therefore saponification value = (3 x 56 x1000) /638 =263.3 mg of KOH/ g of fat

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