Thomas Stambek

Experiment 3.1

Melting Point

CHEM 241L

Section 803

September 16, 2010

Discussion and Conclusions

In this experiment we were asked to determine the melting points of several substances. We

were instructed on the proper use of a metal-block apparatus. The substances that we measured the

melting point of were, Biphenyl, Mandelic Acid, T-Cinamic Acid, mixtues of T-Cinamic Acid and

Urea. The purpose of this experiment was to properly measure a substances melting point, to see the

effects of impurities in a substance on its melting point, and to determine an unknown substance from

its melting point.

In our experiment, we discovered that the melting point range of Biphenyl was 70° C – 72° C.

The Mandelic Acid's melting point range was 109° C – 114° C. The T-Cinamic Acid we measured had

a melting point range of 126° C – 129° C. We then measured the mixtures of T-Cinamic Acid and the

Urea in the following concentrations, Urea:T-Cinamic Acid 25:75, Urea:T-Cinamic Acid 50:50, Urea:T-

Cinamic Acid 75:25. The melting point range of the 25:75 mixture was 107° C – 110° C. The melting

point range of the 50:50 mixture was 98° C – 100° C. The melting point range of the 75:25 mixture

was 99° C – 125° C. We also tested our unknown which had a melting point range of 79° C – 82° C.

Our conclusion was that our unknown was Vanilin.

Impurities can alter the melting point of a substance, even if we know the melting points of all

of the substances in the mixture. This experiment demonstrated the effects that those impurities have

on a substance's melting point.

Questions

1. You should use a small sample in the capillary to determine the melting point because larger

samples would require more heat to melt and give you a broader melting point range. The

sample should be tightly packed so that the heat is evenly distributed across the whole sample

and an accurate melting point is given.

2. Atmospheric pressure will only have a slight effect on melting point at low increases or

decreases. The larger the change in pressure the more the melting point will be effected. The

higher the pressure, the higher the melting point.

3. Rapid heating on a sample will give a broader melting point range because it takes time for the

sample to absorb the heat and melt.

4. A student could measure the two knowns to determine the melting points. Then you could

measure the unknown mixture and see if it falls along the graph of the two known substances.

5. The sample either decomposed or is polymorphic.