Question

Which one of the following has the lowest boiling point?

• A. ${\mathrm{CH}}_3\mathrm{I}$
• B. ${\mathrm{CH}}_3\mathrm{CI}$
• C. ${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{CI}$
• D. ${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{Br}$

Answer 1

The correct option is B

${\mathrm{CH}}_3\mathrm{CI}$

Explanation for correct option

(B) ${\mathbf{CH}}_{\mathbf{3}}\mathbf{CI}$

Boiling point

• The boiling point is determined by ionic bonding, intermolecular interactions, molecule structure, and size.
• The type of functional group attached to the molecule has an impact on the parameters.
• The boiling point measures the strength of the interaction between the molecules.
• The boiling point of alkyl halides increases as the number of carbon atoms in a straight chain increases.

Chloromethane

• All of the molecules in the provided set are alkyl halides.
• The difference in molecular weights between these molecules is the key to their boiling.
• The boiling point of a substance increases with its molecular weight or molar mass.
• Alternatively, the boiling point decreases as the molar mass decreases.
• The boiling point order:

${\mathrm{CH}}_3\mathrm{Cl}<{\mathrm{CH}}_3\mathrm{l}<{\mathrm{C}}_2{\mathrm{H}}_5\mathrm{Cl}<{\mathrm{C}}_2{\mathrm{H}}_5\mathrm{Br}$

• Hence, the ${\mathrm{CH}}_3\mathrm{CI}$ has the lowest boiling point.

Explanation for incorrect options

• The ${\mathrm{CH}}_3\mathrm{CI}$ has the lowest boiling point.
• Hence all other options (A), (C) and (D) are incorrect.

Therefore, the correct option is (B) ${\mathbf{CH}}_{\mathbf{3}}\mathbf{CI}$.