Determination of Freezing Point

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Determination of Freezing Point Ian Sager Introduction: The physical properties of a compound, such as freezing point and boiling point can provide useful information which can help in the identification of a sample or to establish its purity. The temperature a solid melts and becomes a liquid is the melting point. This same temperature allows a sample to freeze, known as the freezing point. Since this temperature is dependent on the amount of energy needed to overcome the intermolecular forces in the sample, the temperature at which freezing occurs depends on the structure of the molecule involved.[i] Experimental: A beaker (600 mL) was filled three-fourths of the way with water and left to boil. While the water was boiling, stearic acid was added into a glass tube and positioned, with a clamp, over the boiling water. A thermometer and glass stirring rod were placed in the tube. When the water reached a boil, the flame was turned as low as possible and the tube was lowered into the water. The solid acid was stirred until it liquified. The acid was stirred until it reached 80°C, then the tube was moved out of the water and suspended away from the beaker entirely. When the temperature reached 78°C the temperature was then recorded at 30-second intervals for 8 minutes. The acid was continuously stirred throughout this process. This whole process was then repeated for a second set of data. Results: Table 1: Temperature Data Actual freezing point of acid = 68.8 °C[ii] Percent error = 1 - (1 / 68.8°C * 68°C) * 100 = 1.2% error Discussion: If the temperature was not monitored correctly, there could be a huge source for error. It is difficult to add heat energy to a sample in a uniform fashion. This was done quite well in the melting point section of the experiment because the results are very close to the reference value. Based on calculations, the

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