Question

What effect does branching of an alkane chain have on its melting point?
A.Increase its melting point
B.Decreases its melting point
C.Doesn’t change its melting point
D.Cannot be determined

Answer 1

Hint: The compounds composed of carbon and hydrogen are known as hydrocarbons, these hydrocarbons are carbon derivatives so these are also considered as organic compounds. Alkane is a cyclic saturated hydrocarbon. The general formula of alkane is $C_n{H}_{2n+2}$ where $n$ is integer.

Complete step by step answer:
Branching of alkane or branched alkane are the acyclic saturated hydrocarbons which have alkyl groups attached or bonded to its central atom. Branched alkanes contain only carbon and hydrogen atoms and the molecules contain branches of alkyl groups.
As the branching is done in a molecule or the branches increase the surface area of the molecule decreases which results in the decrease of van der waals attraction. Due to decrease in attraction it becomes easier to overcome a molecule, at low temperature we can overcome it, hence the boiling point of an alkane decreases on branching.
Due to branching the surface area of molecules decreases which makes it more compact, it will be easier to pack them tightly and it will be hard to break that compact structure so this explains that due to branching the melting point increases.
Hence, option (A) is correct, increasing its melting point.

Note: Melting point and boiling point, both the factors depend on the surface area and branching. As the branching is done in an alkane its surface area decreases, this results in decrease of boiling point and increase in melting point, so we can say that surface area $\propto$ melting point.