May 12, 2015
Aradhna Sharma May 12, 2015
Melting Points of Organic Compounds
In this lab, it was observed that pure compounds have a sharp, narrow melting range, while impurities caused the melting point range to become relatively lower and broader. The unknown sample was identified as trans-cinnamic acid. The true melting point range of the unknown compound was 132.5- 135°C which is extremely close to the experimental melting point range for trans-cinnamic acid, which was 133-135°C. The mixed melting points of the unknown sample and the other three known compounds, urea, ASA and benzamide, were low and broad. This is evident as the melting point ranges are significantly lower (approximately 6 degrees Celsius) less than the true melting points of both the unknown and known compounds in each of these cases. However, the true and mixed melting point for the trans-cinnamic acid and the unknown compound are extremely similar which indicates that they are the same compound. Also, the mixed melting point range is sharp, with a range of 2°C, which indicates a pure organic compound. The literature value of trans-cinnamic acid is 134°C, which falls within the experimental melting point range.
The mixed melting range for the unknown sample and trans-cinnamic acid was sharp, narrow and was almost identical melting point range as the unknown compound and trans-cinnamic acid. This allowed for the identification of the unknown sample as trans-cinnamic acid. Also, the literature melting points for benzamide, urea, ASA and trans-cinnamic acid fell within the experimental melting point range for each compound, so these samples were eliminated as possible outcomes for the unknown compound. The literature melting point of 132.4°C for urea fell within the experimental melting point range of 131-133°C. The literature melting point of 136°C for ASA was in accordance with the higher end of the experimental melting point range of 134-136°C. The literature melting point of 134°C for trans-cinnamic acid fell within the experimental melting point range of 133-135°C. The literature melting point for benzamide of 128°C in accordance with the lower end of the experimental melting point range.
The slight error of 0.5 °C (or 25% error) that occurred between the difference in the melting point range of the unknown sample and trans-cinnamic acid, indicated the presence of impurities and/or human…