Constructing Heating/Cooling Curve
| Chemistry Lab Report | Constructing Heating/Cooling Curve | | Salman Ishaq 12-E | 1/27/2013 |
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BACKGROUND
As energy flows from a liquid, its temperature drops. The entropy, or random ordering of its particles, also decreases until a specific ordering of the particles results in a phase change to a solid. If energy is being released or absorbed by a substance remaining at the same temperature, this is evidence that a dramatic change in entropy, such as a phase change, is occurring. Because all of the particles of a pure substance are identical, they all freeze at the same temperature, and the temperature will not change until the phase change is complete. If a substance is impure, the impurities will not lose energy in the same way that the rest of the particles do. Therefore, the freezing point will be somewhat lower, and there will be a range of temperatures instead of a single temperature.
PROBLEM
To evaluate the samples, you will need a heating/cooling curve for pure Na2S2O35H2O that you can use as a standard. To create and use this curve, you must do the following.
• Obtain a measured amount of pure Na2S2O35H2O.
• Melt and freeze the sample, periodically recording the time and temperature.
• Graph the data to determine the melting and freezing points of pure
Na2S2O35H2O.
• Interpret the changes in energy and entropy involved in these phase changes.
• Verify the observed melting point against the accepted melting point found in reference data from two different sources.
• Use the graph to qualitatively determine whether there are impurities in a sample of Na2S2O35H2O.
OBJECTIVES
Observe the temperature and phase changes of a pure substance.
Measure the time needed for the melting and freezing of a specified amount of substance.
Graph experimental data and determine the melting and freezing points of a pure substance.
Analyze the graph for the relationship between melting point and freezing point.
Identify the relationship between temperature
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BACKGROUND
As energy flows from a liquid, its temperature drops. The entropy, or random ordering of its particles, also decreases until a specific ordering of the particles results in a phase change to a solid. If energy is being released or absorbed by a substance remaining at the same temperature, this is evidence that a dramatic change in entropy, such as a phase change, is occurring. Because all of the particles of a pure substance are identical, they all freeze at the same temperature, and the temperature will not change until the phase change is complete. If a substance is impure, the impurities will not lose energy in the same way that the rest of the particles do. Therefore, the freezing point will be somewhat lower, and there will be a range of temperatures instead of a single temperature.
PROBLEM
To evaluate the samples, you will need a heating/cooling curve for pure Na2S2O35H2O that you can use as a standard. To create and use this curve, you must do the following.
• Obtain a measured amount of pure Na2S2O35H2O.
• Melt and freeze the sample, periodically recording the time and temperature.
• Graph the data to determine the melting and freezing points of pure
Na2S2O35H2O.
• Interpret the changes in energy and entropy involved in these phase changes.
• Verify the observed melting point against the accepted melting point found in reference data from two different sources.
• Use the graph to qualitatively determine whether there are impurities in a sample of Na2S2O35H2O.
OBJECTIVES
Observe the temperature and phase changes of a pure substance.
Measure the time needed for the melting and freezing of a specified amount of substance.
Graph experimental data and determine the melting and freezing points of a pure substance.
Analyze the graph for the relationship between melting point and freezing point.
Identify the relationship between temperature