Question

Which of the following chemical reactions could be used to distinguish between a polyunsaturated animal oil and a synthetic cooking oil containing a mixture of saturated and unsaturated hydrocarbons? Explain your reasoning.

1. Addition of iodine in
2. Hydrogenation
3. Saponification with
4. Ozonolysis

Short answer

Saponification is a reaction of an ester, so only the vegetable oil will react and not the hydrocarbon oil mixture. With saponification of a vegetable oil, as sodium hydroxide is consumed, the pH value would drop and with a petroleum oil, the pH value would not change.

Step-by-step solution

Step-1. Reason for why reagents (a), (b) and (d) will not be able to distinguish:

Reagents such as iodine in carbon tetrachloride, hydrogen with platinum or palladium catalyst and ozonolysis whether reductive or oxidative would not be able to distinguish between a polyunsaturated animal oil and a synthetic cooking oil containing a mixture of saturated and unsaturated hydrocarbons, because all these reagents would react with alkenes or double bonds present in reaction mixture and no difference would be observed.

Step-2. Saponification as a distinguishing test:

Saponification is a reaction of ester, so only the vegetable oil would react and not the hydrocarbon oil mixture. With saponification of vegetable oil, as sodium hydroxide is consumed, the pH value would drop gradually and with a petroleum oil, the pH value would not change. Vegetable oils and animal fats are fatty esters in the form of triglycerides. The alkali breaks the ester during saponification and releases the fatty acid salt and glycerol.