Question

1. Drying of sample in Diels Alder Reaction lab experiment

a) Why must a sample be completely dried before its melting point can be determined?

b) How can it be ascertained that a sample is thoroughly dry?

Answer 1

a) If there are even traces amount of impurity may change the melting point or increase the melting point range. This results in a deviation from actual results. Impurities like water may show strong association or dissociation with product molecules. The impurities replace the molecules from the crystal lattice and that leads to change in thermodynamic properties of the crystal.

To avoid such deviations sample must be completely dried  

b) There are several ways to make sample dry, such as

i) dry under the Infra-red lamp

ii) Dry with the high power succession pumps in the desiccator

iii) Dry the sample for enough amount of time until it becomes free crystals

iv) Handle the dried crystals in desiccator so that it does not absorb moisture from the atmosphere

v) handle the sample with gloves