Question

Select the true statement:
(A) Boiling point order: $RF > RCl > RBr > RI$
(B) Haloalkanes are highly soluble in water
(C) Melting point order: p-dichlorobenzene > o-dichlorobenzene
(D) Density order: $RCl > RBr > RI$

Answer 1

Haloalkanes are the class of compounds composed of alkane and halogen atoms. The haloalkanes are heavier than the corresponding alkanes and are dipolar in nature.

Complete step by step answer:
The properties of haloalkanes clearly indicate the truth or false of the given statements. Let us evaluate the statements one by one.
(A) Boiling point order: $RF > RCl > RBr > RI$.
The electronegativity difference between halogen and carbon atoms results in the polarization of carbon halogen bonds. Down the group from fluorine to iodine the molecular size and its mass increases as well as the bond polarity which results in strong intermolecular forces of attraction. Hence the boiling point increases down the group. Thus the boiling point order is $RF < RCl < RBr < RI$ and the statement is false.
(B) Haloalkanes are highly soluble in water.
Haloalkanes are slightly soluble in water. The bond between halogen and carbon is covalent in nature. Water is polar solvent so it can dissolve the compounds which can ionize completely in water or compounds which can form hydrogen bonds with water. Haloalkanes neither ionize completely in water nor do they form hydrogen bonds. Hence the statement is false that haloalkanes are highly soluble in water.
(C) Melting point order: p-dichlorobenzene > o-dichloro benzene
The compound having a high melting point has high lattice energy. The high lattice energy is the result of strong intermolecular forces between the bonded molecules. The strong molecular force is due to the compact bonding of present in para isomers than ortho and meta isomer. The para isomer has more symmetrical structure than ortho and meta isomers. Hence, more energy is required to break the crystal lattice of para isomers. Thus, p-dichlorobenzene has a higher melting point than o-dichlorobenzene.
(D) Density order: $RCl > RBr > RI$
Density of a compound is directly proportional to the mass of the compound. Down the group, density increases as mass increases from fluoro to iodo. Hence fluoro derivatives are less dense than chloro derivatives, chloro derivatives are less dense than bromo derivatives and bromo derivatives are less dense than iodo derivatives. Thus the density order of $RCl > RBr > RI$.

Note:
The boiling point of haloalkanes decreases with branching. The haloalkanes are only very slightly soluble in water, but dissolves readily in organic solvents.