Question

The melting point of Unsaturated Fatty acids
A. Increases with increase in double bonds
B. Decreases with increase in double bonds
C. Rises in some and falls in other
D. There is no relationship between unsaturation and melting point

Answer 1

Hint: The double bond has a cis configuration due to which its intermolecular interactions are weak resulting in the low melting point.

Step by step answer:Unsaturated Fatty acids are those acids that have double or triple bonds in them. These unsaturated double and triple bonds cause the respective Fatty acids to be liquid at room temperature.
The basic chemistry of double bonds tells us that it has a cis configuration. This means that similar kinds of groups are attached on the same side of the double bond. This cis configuration is responsible for weak intermolecular interactions. Due to these weak intermolecular interactions, the melting point is low. As the number of the cis bonds increases the intermolecular interactions reduce further. This causes the melting point to go down further. Therefore, the double bonds are actually reducing the melting point. Thus, the melting point of unsaturated Fatty acids decreases with an increase in double bonds.
Hence, the correct answer is option (B).

Note: Unsaturated Fatty acids can be converted to the Saturated Fatty acids that contain only double bonds. This process is known as Hydrogenation. Saturated fatty acids are solids at room temperature. Hydrogenation is the process in which the hydrogen atoms are added to the double bond in order to reduce them to a single bond. The catalysts that are required for this reaction are Nickel, Platinum, and Palladium.