Degree of Unsaturation with Iodine & Saponification of Fatty Acids
Abstract
In this lab different oils including sunflower oil, castor oil, grapes oil, avocado oil and unknown
oil were tested for their degree of unsaturation using iodine and their soap characteristics were
determined using sodium hydroxide. It was found that, grape seed oil has highest degree of
unsaturation, whereas, sunflower has least. The decreasing order of unsaturation is grape seed oil
< unknown oil < castor oil < avocado oil < sunflower oil. Moreover, the soap formation
characteristic of the oils in increasing order is Sunflower oil < Avocado oil < unknown oil < castor
oil < grape seed oil. The effect of hard water and soft water on soap formation was also determined.
When soft water was added to the oil, it was found that hand soap oil is most sudsy and sunflower
is most least sudsy. However, when Magnesium sulfate was added to each vial no effect was
measured (it could be error) because magnesium sulfate should reduce the soapy nature of the oils.
Introduction
An unsaturated hydrocarbon is a molecule made of carbon and hydrogen atoms that does not
contain the maximum number of hydrogens possible. An alkene is an unsaturated hydrocarbon.
The general formula for calculating the degree of unsaturation is:
degree of unsaturation = C – H/2 - X/2 + N/2 + 1
Using this equation, C represents the number of carbon atoms in the molecule, H represents the
number of hydrogen atoms, X represents the number of halogen atoms, and N represents the
number nitrogen atoms.
Cooking oils are a common example of fatty acids. Some cooking oils are saturated fatty acids,
and some are unsaturated. The difference is a double bond. All fatty acids have a carboxylic acid
on one end of the molecule. In this lab different oils including sunflower oil, castor oil, grapes oil,
avocado oil and unknown oil were tested for their degree of unsaturation using iodine and their
soap characteristics were determined using sodium hydroxide
Procedure
As given in the lab manual.
Results
Addition of iodine on oils
2. order of degree of unsaturation
The decreasing order of unsaturation is grape seed oil < unknown oil < castor oil < avocado oil <
sunflower oil.
3. Effect of Sodium Hydroxide and Soft water in oils
4. Effect of MgSO4 in oils
5. order of Least Sudsy to Most Sudsy oil
Discussion and Conclusion
Sunflower oil, castor oil, grapes oil, avocado oil and unknown oil were tested for their degree of
unsaturation using iodine and their soap characteristics were determined using sodium hydroxide.
It was found that, grape seed oil has highest degree of unsaturation, whereas, sunflower has least.
The decreasing order of unsaturation is grape seed oil < unknown oil < castor oil < avocado oil <
sunflower oil. The literature says grape seed oil contains more than 80 % unsaturated compounds,
out of them 70 % linolenic acid and 16 % oleic acid. Grape seed oil contains 80% of poly
unsaturated fatty acids. The reaction of linolenic acid with iodine is as following;
Castor oil contains 85-95% ricinoleic acid is the main component.
Avocado oil contains 13.5% total polyunsaturated fatty acids and 71 % monounsaturated fatty
acids.
linoleic acetogenin
Sunflower oil contains 3.8 % total polyunsaturated fatty acids and 83% monounsaturated fatty
acids. The structure is given in the following;
Moreover, Soap characteristic of oils was also determined and observed increasing order of soapy
nature of the oils, Sunflower oil < Avocado oil < unknown oil < castor oil < grape seed oil. So,
based on the literature, we conclude that grape seed contains highest percentage of poly
unsaturated fatty acids and therefore, it showed greater extent of soap formation characteristic and
sunflower has least due to less polyunsaturated fatty acid chains. The saponification reaction is
given as following.