Lam Gary Experiment 2: Mixed Melting Points Discussion: Part I) After I got my unknown sample, which consisted of small white particles, and found the melting point range via melting point analysis, I looked for someone with around the same melting point (within 4C). I found two people, partner 1 with a sample that looked like mine and partner 2 with a sample that consisted of opaque, white crystallized particles that were slightly bigger than mine. With each partner, we used melting point analysis after mixing our two samples. The mixed sample with partner 1 had the same melting point range as my pure sample. The mixed sample with partner 2 had a lower melting point that my pure sample. Since impurities decrease the melting point range and the sample with partner 1 had the same melting point as my pure sample, I could identify that partner 1 and I had the same unknown solid. Part II) The eutectic point occurs around the 40:60 ratio composition of A:B. In the diagram, this is where the average final melting temperature is the lowest. In the raw data, this is where the final temperature is most depressed. For the final average temperatures for 70:30 and 30:70 compositions on the graph, I excluded one data from point each composition because there was a large difference and I considered the data point an outlier. These outliers could have been the result of human error via misreporting the data. Part III) The melting point range of my unknown mixture of A and B was 50.4 C to 68.9 C. Based on the diagram, the composition of my mixture could be either in a ratio of about 75:25 or 15:85 of A:B. To determine the actual composition of my mixture, I
would create two mixtures, each with one part of my unknown mixture, and add an equal part of the 75:25 composition mixture to one and an equal part of the 15:85 composition to the other. Then I would do a melting point analysis and look at the melting point ranges of the two mixtures. If one has about the same as my pure unknown mixture and the other has a depressed and broader melting point range, I would know that the mixture with about the same melting point range is the composition of my mixture. Conclusion: I learned how to do a melting point analysis using Melt-temp and learned about observing melting point ranges. I also learned how to determine the identity of an unknown compound by comparing melting points and doing a mixed melting point analysis.