Fusion Experiment

Purpose :

The main purpose of this experiment was to identify an unknown compound/substance by performing multiple experimental melting point tests. Pure and impure solids were tested to see what affect pureness/impureness had on a melting point.

Background:

The melting point of a solid can be used to determine the purity of the solid. Pure samples usually have identical or similar melting points. Given this information, the identification of an unknown solid could be determined by comparing its experimental melting point to an accepted literature value of a known substance. Pure solids always have higher melting points and smaller melting point ranges. When an impurity is present in a solid sample, the melting point will be lower and the melting point range will be wider.

Materials:

The materials used in this experiment were Urea: CH4N2O and Cinnamic Acid: C9H8O2, and an unknown substance. The melting points were determined using an electronic melting point apparatus which utilized capillary tubes to hold the samples for observation.

Experimental Procedure:

Samples of pure cinnamic acid, urea, and an unknown substance were obtained. They were each placed into their own container and labeled. A very small amount of each substance was packed into its own capillary tube. The capillary tubes were placed inside the melting point apparatus and a melting point range was determined for each substance. To determine the melting point range, the sample was observed thru a magnifying lens. When the sample began to melt, the temperature in which it began to melt was recorded. When the entire sample had melted the final melting point was recorded. This allowed for a melting point range. Two melting point trials were performed for each sample to ensure accuracy. Once the melting points of the pure samples were obtained, mixed melting points were observed. Cinnamic acid and urea were mixed using a 1:1 ratio and the melting point range was determined. To determine the identity of the unknown substance, a mixture of cinnamic acid and the unknown was made, as well as a mixture of urea and the unknown substance. The melting points of these mixtures were obtained. The resultant melting points allowed for accurate identification of the unknown substance.

Results/Data:

Compounds and Their Melting Points

Compound/Mixture Melting Point Range (Trial 1)

Melting Point Range (Trial 2)

Unknown 132o-134o 132.4o-134.2o

Cinnamic Acid 133.1o-134.4o 133.5o-135.8o

Urea 131.7o-135.1o 131.4o-134.6o

Cinnamic acid: Urea mixture 101.0o-128.2o 98.