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Unformatted text preview: Experiment 5: Ideal Solutions Author: Ben Rainey Group 2 Section 3, T 2:00 PM 5:00 PM Partner: Ben Huffer December 7, 2010 Abstract : In this experiment, ideal solutions and deviations from ideality were studied. The two main scientific goals were to determine the excess enthalpy and excess volume of mixing water and methanol. A two-drop calorimeter was used to determine the excess enthalpy of mixing and a series of pycnometers was used to determine the excess volume of mixing. By varying the mole fraction of water, it was found that the largest magnitude of the excess enthalpy of mixing was -11.2 J/mole and this occurred at a water mole fraction of 0.564. The negative value indicates that the reaction was exothermic. It was also found that the largest magnitude of the excess volume of mixing was -0.95 mL/mole and this occurred at a water mole fraction of 0.4. The excess functions of mixing had much lower magnitudes towards the extrema of mole fractions of water. This corresponds to the solutions behaving more ideally. Solutions deviate from ideality more and more as the components in the solutions are mixed together in an equal proportion. I. Introduction Experiment 5: Ideal Solutions The excess function of mixing is one method used to measure the ideality or non- ideality of solutions. An ideal solution is a solution in which the solute-solvent interactions are the same as those between solute-solute and solvent-solvent molecules. Two of the common functions measured in excess functions of mixing include enthalpy and volume. In order to see the deviations from ideality as a function of solute or solvent concentration, the mole fraction of one component can be varied and then the excess function of mixing can be measured at that mole fraction. The results from these experiments can then be analyzed and trends can be generated. This experiment had two main objectives. The first objective was to determine the excess enthalpy of mixing for mixtures of water and methanol. The second objective was to determine the excess volume of mixing for mixtures of water and methanol. In order to obtain the excess of enthalpy of mixing of a solution, a two-drop calorimeter can be used. As opposed to the more common calorimeters used in undergraduate labs, a two-drop calorimeter is maintained as a constant temperature and heat is allowed to flow into or out of the mixture. The more common bomb calorimeter uses an adiabatic system, and then uses the heat capacity of the material or solution of interest and the change in temperature in order to measure the heat absorbed or generated by the system. In the two-drop, isothermal calorimeter, the production or consumption of heat is allowed to move into a constant temperature block (a heat sink). A thermochemical device placed between the reaction vessel and heat sink measures and amplifies the heat exchange and converts the corresponding value to a digital heat flow value that can be read off of the computer. By graphing heat flow versus time, one can value that can be read off of the computer....
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