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Investigating Phase Changes

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Introduction

Nicole Calo September 5, 2008 Chemistry Ms. Semkin INVESTIGATING PHASE CHANGES: Heating and Cooling Curves Background information Pure matter can exist in three phases: solid, liquid, and gas. A change of phase takes place when matter changes from one phase to another. Phase changes take place when heat is given or taken away from a substance. The melting point of a substance is the temperature at which the solid turns into a liquid. The freezing point is the temperature at which the liquid turns into a liquid. The melting point of a substance is the same as its freezing point. At this temperature, solid and liquid can exist together. Purpose 1) Determine what temperature changes occur when a substance changes phase. 2) Determine the melting point (freezing point) of a pure unknown substance. 3) Identify the unknown pure substance in your test tube. Materials Safety glasses Test tube with unknown substance in it Utility clamp Test tube holder Stop watch Celsius thermometer Ring stand Bunsen burner Ring clamp Wire mesh Beaker 250ml Beaker 500ml Matches Pendulum stand Gas source Stirring rod Procedure Part 1 Heating Curve 1) ...read more.

Middle

2) Be sure to include observations such as when the liquid pure substance first starts to solidify and when the substance has completely solidified. 3) Do not try to pry out the thermometer from the test tube else it be damaged. Put back the unknown substance with the thermometer in it to where you got it. Do not throw in the garbage or down the sink. 4) Clean up and put everything else back. Data Table Table 1: Heating Curve Time (minutes) Temperature (Celsius) Time (minutes) Temperature (Celsius) 0 24 6.5 45 0.5 25 7 47 1 26 7.5 49 1.5 26.5 8 53 2 27 8.5 57.5 2.5 28 9 59 3 28.5 9.5 60.5 3.5 29 10 62 4 31 10.5 63.5 4.5 32.5 11 65 5 35 11.5 66 5.5 37 12 67 6 41.5 Table 2: Cooling Curve Time (minutes) Temperature (Celsius) Time (minutes) Temperature (Celsius) 0 67 6.5 41 0.5 64 7 41 1 53 7.5 40.9 1.5 48 8 40.5 2 46 8.5 40 2.5 44.5 9 ...read more.

Conclusion

Therefore, it is most likely that the unknown substance is Phenol Salicylate. 3) Freezing is Endothermic. Melting is exothermic. 4) The diagonal parts of the cooling curve represent the decreasing kinetic energy and decreasing potential of the substance's atoms as they are being cooled or removed of heat energy. The horizontal portions of the cooling curve represent the steady kinetic energy and increasing potential energy of the atoms as they gain energy to bond closer together as a solid. Conclusion Based upon the gathered data and graph calculations, we have identified the unknown pure substance as Phenol Salicylate because of the unknown substance's near matching melting-freezing point of 42.5 degrees Celsius to that of Phenol Salicylate which has a freezing-melting point of ~43-46 degrees Celsius. Also the unknown substance did not give off any smell, therefore we eliminate the possibility of it being Lauric Acid. Likewise, the substance's melting-freezing point is much to far from that of the other possible acid, Stearic acid which has a freezing-melting point of ~67-69 degrees Celsius. ...read more.

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