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

2. Another student reports melting range of 136 - 138 degree C for the compound in Question 1 and mentions in her notebook that the rate of heating was about 12 degree/ min. NMR analysis of this student's product does not reveal any impurites, explain the low melting point.