Question

question 4 - 1 point
the melting point of phenol is 40.5^{circ}c and that of toluene is - 95^{circ}c. what is the best explanation for this difference?
select the correct answer below:
the (-oh) group on phenol can form hydrogen bonds, and the -ch_{3} group on toluene cannot.
phenol has only one hydrogen on the -oh group available to form hydrogen bonds, so the hydrogen bond is stronger. in toluene, the hydrogen bond is spread over all three hydrogens on the methyl group, so the interaction is weaker overall.
phenol has a higher molecular mass than toluene.
none of the above.

Explanation:

Hydrogen bonds are strong intermolecular forces. Phenol has an -OH group which can form hydrogen bonds (between the O of one phenol molecule and the H of the -OH group of another phenol molecule). Toluene has a -CH₃ group. The -CH₃ group cannot form hydrogen bonds. Substances with stronger intermolecular forces (like hydrogen - bonded substances) generally have higher melting points. Phenol's higher melting point is due to hydrogen bonding, while toluene lacks this strong intermolecular force.

Option B is incorrect because toluene cannot form hydrogen bonds at all (not that its hydrogen - bond is spread over three hydrogens). Option C is incorrect as molecular mass difference is not the main reason here (phenol's formula is \(C_6H_5OH\) with molar mass \(94.11\space g/mol\), toluene's formula is \(C_6H_5CH_3\) with molar mass \(92.14\space g/mol\), the mass difference is small and not the cause of the large melting - point difference). So, option A is the correct explanation.

Answer:

A. The (-OH) group on phenol can form hydrogen bonds, and the -CH₃ group on toluene cannot.