University of Central Florida (UCF) CHM2211L Organic Laboratory Techniques I Final Practice Exam

A broad melting point range is indicative of a compound being likely impure. In organic chemistry, the melting point of a pure crystalline substance should be sharp and occur at a specific temperature. Impurities disrupt the orderly packing of molecules in the crystal lattice, lowering the melting point and broadening the range over which the melting occurs.

When a compound has impurities, the presence of different substances can cause variations in intermolecular interactions, which affects how the material transitions from solid to liquid. As a result, the melting point range can expand significantly, leading to uncertainties in determining the precise melting point of the overall sample. Thus, a broad melting point range serves as a strong indicator that the sample is not pure, signifying the presence of one or more impurities mixed with the desired compound.

In regards to the other options, a pure compound would typically show a sharp melting point, so a broad range would contradict that notion. While the compound might theoretically have multiple phases, that’s not a direct implication of the melting point alone. Lastly, improper crystallization could lead to some broadening of the melting point range, but this would not universally apply to every sample with this characteristic.