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Prelabexercise if 10gofethanol c2h5oh is dissolved in

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Unformatted text preview: to + ­ form two moles of ions (Na and Cl ). Because colligative properties are related to the number of solute particles, we would expect a mole of NaCl to have twice the effect as a mole of ethanol. Therefore, (i =1) for ethanol and other non electrolytes, (i =2) for NaCl, and (i = 5) for Al2(CO3)3. Prelab Exercise: If 10g of ethanol, C2H5OH, is dissolved in 100 g of pure water, what would the boiling point and freezing point be for this solution? First determine the molality of the solution: For water the Kb = 0.512°C/m, and Kf = 1.86°C/m. Calculate DTb and DTf for this solution: Page 2 of 9 Chemistry 52 Method: In this experiment you will need to determine the freezing point depression for several solutions. However, the temperature at which a solution freezes is diff icult to determine by direct visual observation because of a phenomenon called super cooling and also because solidification of solutions usually occurs over a broad temperature range. To overcome these problems, temperature­time graphs, called cooling curves, are used which readily reveal the true freezing temperature. The major features of a general cooling curve are shown below: You will construct cooling curves for both the pure solvent (water) and various solutions. From the cooling curve you will extrapolate the true freezing temperature. Extrapolation is necessary because as the solution freezes the solid that is formed is essentially pure solvent. The remaining solution becomes more and more concentrated and its freezin...
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