Physical Properties of Organic Molecules
Identifying the physical properties of compounds can be useful in several ways. It helps us to determine the structure of certain compounds, the purity of substances and if a substance is not pure we can figure out how to separate contaminating substances from a compound. In this experiment, I learned how to determine a solid’s melting point and why some melting point ranges may be broader than others. From my data, I also determined that water is not a good solvent for a lot of solids even when it is boiled. Also, when looking at boiling point, my data showed that ethanol has a low boiling point so it made me investigate further to see why that happened. Introduction
All substances have properties that we can use to identify them. For example, we can identify a person by their voice, height, face, finger prints. The more of these properties we can identify the more we know the person. In a similar way, matter has properties and there are many of them. The two basic properties we associate with matter are physical and chemical properties. Physical properties are those properties that do not change the chemical nature of matter. Chemical properties are those properties that do change the chemical nature of matter. All physical and chemical properties observed for a compound are directly related to the compound’s molecular structure. The most common physical properties are color, odor, crystalline form (if it’s a solid) ,refractive index (if it’s a liquid), density, solubility in various solvents, melting point (for solids), and boiling point (for liquids). In this experiment, we will use melting point, boiling point, and solubility to identify certain solids and liquids. First, we will melt benzoic acid, benzoin, and an unknown substance. I believe the benzoin will have a small range melting point because it is a pure substance. Since the benzoic acid has impurities it will have a wider range melting point. In determining boiling point, we will use ethanol and an unknown substance. I believe ethanol will have a lower boiling point than water because water has a hydrogen bond and the molecules stick together which means you need more heat to break water apart. Ethanol has London forces which requires less heat to break the molecules apart.2 In the final part of the experiment, we will test the solubility of certain solvents. Benzoic acid, Napthalene, NaCl, and Benzoin will be tested. I do believe that water will not dissolve any of the solids. If certain solids are insoluble or partially soluble they must be boiled to see if they will eventually dissolve.
In the melting point experiement, pure urea was not used. Benzoin was substituted for the pure urea. In the solubility experiment, Benzoin was used again in place of the pure urea. Literature procedure was followed for remaining steps. 1
Results- Please refer to handwritten copy of data.
In the melting point experiment, benzoic acid had a broad melting range that suggested the substance was not very pure. However, my hypothesis was correct about the Benzoin. The melting range was 3 degrees apart which suggested Benzoin is more of a pure substance. In the boiling point portion of the experiment, ethanol boiled at 76 degrees, which suggested it requires less heat to break the molecules apart as I hypothesized. In the solubility part of the experiment, my hypothesis was not entirely correct as water was soluble in NaCl. However, it was insoluble to the remaining solvents. The solubility of certain solvents varied greatly based on the chart. I also noticed that after boiling a few of the solvents that were insoluble or partially soluble they did dissolve a little more. Example, Benzoin went from completely insoluble to soluble in Ethyl acetate.
The physical properties of melting...
Bibliography: 1. Memari, Behnoush Organic Chemistry 1 & 2 lab manual
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