How Can Palmitic Acid Affect The Determination Of Melting Point

Abstract: The goals of this experiment were to observe the changes in melting points across different compounds as well as the factors that affect melting point accuracy, which are impurities and amount of compound. The experiment begins by comparing the effectiveness in obtaining the recovery of a solid from a mixture between gravity and vacuum filtration. Which vacuum filtration had 11% loss while gravity had only a 7% loss. It was determined that pure benzoic acid had a melting range of 122.9-124.4 oC while impure benzoic acid had a melting range of 83.4-86.3 oC. The unknown compound 1 was determined to be palmitic acid through mixed melting point theory. Introduction: The first goal of the experiment was to perform a gravity filtration

The vacuum filtration technique resulted in a 89mg recovery of CaCO3 which was an 11% loss. The gravity filtration had a lower % loss, and therefore a higher percent recovery. The main way to lose the compound was in the flask where the calcium carbonate was mixed with the acetone. It was difficult to transfer all of the calcium carbonate and not leave a small amount of solid residue at the bottom of the flask. The gravity filtration resulted in a higher recovery. We found that gravity filtration is more suitable for the recovery of a solid material.
The capillary tube with a lesser amount of compound melted at a higher temperature than the capillary tube with more compound, as well as having a smaller melting point range. This is because the larger sample size, took longer for the heat to disperse and therefore had a large melting point range.
Table 1: Melting Point range for benzoic acid at various amounts
Compound Reference MP (oC) Observed Melting Range (10oC/min) Observed Melting Range (1oC/min)
Benzoic acid 121-125 122.9-124.4 123.4-126.9 122.5-122.7 121.8-123.1

Table 2: Six melting point compounds with chemical formula, reference, and result melting point
Compound Formula Reference MP (oC) Team Results(oC) Group Results (oC)
Myristic acid C14H28O2 53-56 54.9-56.4
Palmitic acid C16H32O2 61-63 63.0-64.4
Stearic acid C18H36O2 67-72 69.1-71.2

The trend of decreased melting point is a result of the intermolecular bonds and the structure of a compound. Eicosane had the lowest melting point as a result that it lacked an oxygen or hydroxide functional groups and had the most hydrogen bonds. In contrast, mystic acid had the fewest hydrogen bonds and the highest melting point on account of the double bond with the hydrogen. This double bond increased the melting point of the first three compounds, while the higher amount of carbon bonds and hydrogen bonds decreased the melting