Question

An unknown compound gave a melting point of 230 °C. When the melted liquid solidified, it was melted again and found to have a melting point of 150 °C. Give a possible explanation.

Answer 1

One possible explanation could be that the sample liquid trapped some impurities while being solidified. Melting point is characteristic of a material’s solid-state. A solid is mostly a repeating pattern of crystalline lattices of the molecules. Intermolecular forces that make the structure rigid and stabilized hold these lattices together. A certain amount of heat is required to disrupt this structure. However, when impurities come into the picture, they weaken the lattice, thereby, less energy will be required to disrupt the structure and hence, the compound melts at lower temperatures (150℃).

Another possibility could be that the structure that melts at 230℃ is one form of the compound with a particular lattice arrangement. When the compound and solidified again, it acquired a different lattice arrangement with weakened forces holding this structure together. As a result, the new compound melted at lower temperature (150℃).