Biochemistry

Science is a collaborative enterprise, and teams of scientists often work together to make discoveries. It is also common for groups of researchers from different parts of the world to collaborate by sharing experimental data and exchanging samples. The groups must then establish that the samples with which they are working are identical.
How do you know if two compounds are the same? Among organic chemicals, there are many colorless (white) and colored solids and liquids, so a visual inspection is usually insufficient to determine identity. Rather, we must rely upon comparison of measured physical properties. In this experiment, you will be working with your classmates to discover which of you have the same compound and what that compound is. Through solving this puzzle, you will learn some basic techniques for analyzing and identifying organic compounds.
The first part of the puzzle involves measuring physical properties of your compound and comparing them with data obtained by other students. The second part is proving that all the samples with the same or similar properties are indeed identical. Under the same conditions, compounds having comparable properties may be the same, but compounds having different properties are clearly not. Completing the puzzle requires that the compound be identified. In this regard, single measurements by themselves are insufficient for identifying a compound. For example, just knowing that a compound is a clear liquid at room temperature and has a melting point of 0 °C rules out many possibilities, but a variety of compounds melt 0 °C. Knowing that the compound melts at 0 °C, boils at 100 °C, has a density of 1 g/mL, and is soluble in methanol but not in hexane gives us greater confidence that the substance is water. Accordingly, as you collect more data, your confidence in matching compounds that may be the same will increase as will your confidence in establishing the identity of the compound.
You will be given a numbered sample of a colorless pure solid as your piece of the puzzle. The first goal in solving the puzzle is finding who else in the laboratoryhas the same compound as you. To accomplish this task, you will determine some properties of your sample, such as its melting point (Sec. 3.3), its solubility in two solvents (water and aqueous sodium hydroxide), and its $R_{f}$ on a thin-layer chromatography (TLC) plate (Sec. 6.2). You will then share your results by recording the data in a central location to find the other students who have a compound whose properties are the same as or similar to yours. Strategies for making unambiguous comparisons that will ultimately prove the identity of different samples are provided below.
Your laboratory notebook should contain all the data you obtained, as well as a brief compilation of the data reported by the other students whose data are comparable to yours. These labmates and you will have a second goal of determining exactly which compound your group has. To accomplish this objective, the group will be given a list of possible comparison substances to use for making a final identification of the compound. These substances will also be available for actually making the comparisons. As before, suggestions will be provided that allow you to prove the identity of your sample and the comparison compound.

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