chy-142 melting point

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Toronto Metropolitan University *

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599

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Chemistry

Date

Feb 20, 2024

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pdf

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2

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PDF.js viewer https://courses.torontomu.ca/d2l/common/assets/pdfjs-d2l-dist/1.0.14-...dered-pdf&fullscreen=d2|-fileviewer-rendered-pdf-dialog&height=820#0 Name: Oaba Shakil Report Sheet < MIXED MELTING POINT ¢ partner: Christina Mai Part A Melting point of your unknown Unknown # 470 Observed M.P. range 119C-123C Possible Identity #1 Benzoic acid Possible Identity #2 Mandelic acid Parts B & C Mixed melting points with your unknown Unknown # Mixed with M.P. range of mixture 470 Benzoic Acid 112C-125C Mandelic Acid 118C-122C Conclusions Unknown # 470 is actually Mandelic Acid 2023-09-26, 12:33 PM Page 1 of 2
PDF.js viewer 2023-09-26, 12:33 PM QUESTIONS Complete the following questions and submit them with your lab report. 1. What is a melting point range? The term "melting range" refers to the range of temperatures at which a substance changes from a solid to a liquid state. It is a typical physical characteristic used to describe and distinguish chemical substances. The lower and upper temperatures used to illustrate the melting point range typically represent the lowest and highest temperatures at which the substance transforms from a solid to a liquid. 2. How is the melting point range used as a criterion to determine the purity of a sample? A crucial factor in determining a sample's purity is the melting point range. To determine the level of impurity in a substance, it is a useful instrument used in chemistry and materials science. A pure substance often has a well defined melting point, or the temperature at which it changes from a solid to a liquid. Comparing the observed melting point range of the sample to documented literature values for the pure compound is the first step in determining purity. A high level of purity is indicated by the values close agreement with those in the literature. On the other hand, contaminants usually tend to lower the melting point and widen the range. The likelihood of contaminants in the sample is higher the wider and lower the detected range. By including a little amount of a suspected impurity to the sample, mixed melting point tests can be carried out to further establish the existence of impurities and identify probable contaminants. Using various mathematical methods and calibration curves, it is possible tc estimate the percentage of purity of the sample by examining the dip in melting point produced by impurities and the observed melting point range. With applications in areas including medicines, chemistry, and materials science, where purity is crucial for intended uses, the melting point range is a fundamental and frequently used approach for guaranteeing the purity of substances. 3. Why is it necessary to reduce the temperature gradient near the melting point? Is rapid heating liable to result in too low or too high a reading? Explain your answer. When determining a substance's melting point, it is essential to maintain a low temperature gradient nearby because rapid heating might add errors into the data. A sample may experience localised temperature changes inside the substance if it is heated too quickly. As a result, the melting point range may be greater and higher due to some areas melting at slightly higher temperatures than others. As a result, this may overstate the pure substance's actual melting point. A substance's melting point may be underestimated if it is heated too quickly because it may not have enough time to equilibrate evenly throughout. This is because the substance may appear to melt at a lower temperature than it actually does. It is essential to use regulated and gradual heating techniques to reduce temperature variations within the sample in order to obtain precise and trustworthy results. 4. Explain why and how a mixed melting point is able to identify an unknown compound? By comparing an unknown chemical's melting point to that of a known, pure compound, a mixed melting point test is used to identify the unknown component. This method's justification is based on the distinct melting points of pure substances. Several effects can happen when a little amount of the unknown component is combined with an equal amount of the pure reference compound and heated. If the melting points are almost identical, the unidentified substance is probably identical to or extremely comparable to the reference chemical. If the melting point of the combination is lower than that of the pure reference component, impurities are present in the unidentified material. A wider melting point range denotes the possibility of an impurity or another chemical. 5. The mixed melting points of pairs of the following compounds were determined: Compound A (56.5 - 57.2° C); Compound B (56.3 - 57.0°C); Compound C (56.2 - 57.1°C). B+C melts at 56.3 - 57.0° C and A+B melts at 45.1- 53.8°C. Which compounds are the same and which compounds are different? What will be the mixed melting point of A + C? Compounds B and C appear to have very similar melting point ranges based on the mixed melting point data provided (56.3-57.0 °C for B and 56.2-57.1 °C for C), strongly indicating that they are the same or very related compounds. Comparatively, compound A differs from both B and C since it has a distinct melting point range (56.5-57.2 °C) and a noticeably smaller melting point range when combined with B (45.1-53.8 °C). The data given makes it difficult to directly determine the combined melting point of A + C. However, it is reasonable to assume that A + C would have a melting point range comparable to that of A + C, which is 56.3-57.0 °C, given the similarity between the melting temperatures of B and C. According to this, compounds A and C are distinct from one another but have melting characteristics in common with compound B. https://courses.torontomu.ca/d2l/common/assets/pdfjs-d2l-dist/1.0.14-...dered-pdf&fullscreen=d2|-fileviewer-rendered-pdf-dialog&height=820#0 Page 2 of 2
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