Revised 8/29/17 Name Station Date CHM 112 Determination of Molar Mass using Free
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Revised 8/29/17 Name Station Date CHM 112 Determination of Molar Mass using Freezing Point Depression Post Lab Questions cooling curve for any solution does not have a plateau. This indicates that the solution does a constant freezing point. Why did the freezing point of the solution change during the 1. The not have 2. If the unknown solute had actully been an ionic compound instead of a molecular compound fected the calculated molar mass? Provide the reasoning behind your 3. Criticize the following statement. A small amount of the unknown solute in this lowered the freezing point of a solution with cyclohexane below the freezing point of pure cyclohexane. If we had added twice as much unknown solute the freezing point would have decreased even more. So if we had would undoubtedly be much, much lower than the freezing point of pure cyclohexane. the freezing point of the pure unknown solute it 4. Discuss possble sources of errot in this experiment and how those errors would affect the final calculated molar mass. This is an open ended gquestion and a thorough answer is should identify at least three possuble sources of error and discuss the potential effect on the freezing point measurement and the final calculated molar mass. Page 1 of 1Explanation / Answer
1) Cooling behaviour of a pure compound when a liquid cools It decreases in temperature and then solidifies.
A cooling curve is a plot of temperature versus time where energy is released at constant rate.
The freezing point of the solvent and the solution are obtained from a cooling curve - a plot of temperature vs time.The cooling of a pure solvent reaches a plateau at its freezing point.Extrapolation of the plataeu to the temperature axis determine its freezing point.The cooling curve of solution does not reach a plataeu but continues decrease slowly as solvent freezes out of the solution.Its freezing point is determine at the intersection of the two straight lines drwaing through the data points above and below the freezing points.
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