Question

In paraffins, with the increasing molecular weight, it is found that.
(a) Freezing point decreases
(b) Boiling point decreases
(c) Boiling point increases
(d) Vapour pressure decreases

Answer 1

Hint: When the intermolecular attraction between the molecules of a substance is suppressed by the energy of thermal motion. This can be easily understood that the kinetic energy is directionally proportional to the mass and velocity. Generally, the small molecules (with lower molecular weight) possess a lower boiling point than the large molecules (with high molecular weight). But there are some exceptions in which small molecules possess very high boiling points (such as water) compared to other small molecules due to the presence of very strong intermolecular forces.

Complete Step by Step Answer:
Paraffin is a saturated hydrocarbon that is composed of carbon and hydrogen as the major constituent elements.
Paraffin is represented by a \[{C_n}{H_{2n + 2}}\] general formula, Here C represents a carbon atom, H represents a hydrogen atom and n is an integer.
The main source of paraffin is petroleum.
Due to the small electronegativity difference between carbon and hydrogen, the paraffin is considered non-polar and they have the tendency to dissolve in non-polar solvents.
The boiling point of paraffin increases with the rise in molecular weight.
Paraffins with high molecular weight also possess a large surface area. This large surface area of paraffin causes more intermolecular interaction (Van Der Waals forces) between the molecules and as a result boiling point increases.
Therefore, from the above discussion, it is quite clear that option (c) will be the correct answer.

Note: Alkanes have inert and non-polar behaviour with very less reactivity. The availability of methane is very low and it is counted as the main component of greenhouse gases. The branched paraffin has a very slower degradation process than the unbranched paraffin.