Question

of compounds and Mars To: Mening the Making SECTION DATE CHEOL/ M uring the Melting Points of Command Mix Pre-Laboratory Assignment 1. Briefly identify or explain (a) two useful functions served by knowing the melting point of an organic compound (b) why a finely powdered sample should be used in a melting point measurement (c) why it is important to heat a sample slowly to obtain an accurate melting point. (d) two reasons why it is sometimes difficult to measure the temperature at which the crystals first begin to liquefy. (e) what two effects a soluble impurity usually has on the melting point of a compound. (1) what occurred when crystals began to disappear from the bottom of the capillary tube rather than turning to a liquid.

Answer 1

1.

a) By knowing the melting point one can conclude the purity of the sample and identify an unknown compound.

b) Finely packed powdered sample does not contain any air pockets, which inhibits the homogeneous heat transfer in the sample.

c) Slowly heating helps to spread the heat homogeneously and indicate the sharp melting point.

d) It is difficult to measure the the temperature at which the crystals first begin to liquefy when the sample contains impurity and when the heating is done too quickly.

e) It generally decreases the melting point of the sample from the actual value and gives a range of values of melting point of the sample.

f) Crystals began to disappear from the bottom of the capillary tube when the sample sublimates to gas rather than turning to a liquid.