a student performs two melting-point determinations on a crystalline product. in one determination, the capillary tube contains a sample about 1-2 mm in height and the melting range is found to be 141 degree - 142 degree celsius. in the other determination, the sample height is 4-5 mm and the melting range is found to be 141 degree -145 degree. explain the broader melting-point range observed for the second sample. the reported melting point for the compound is 143 degree celsius.