please help.Calculated by the freezing point depression QUESTIONS 1. How would t
ID: 877079 • Letter: P
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please help.Calculated by the freezing point depression QUESTIONS 1. How would the following errors affect the calculated value of the molar mass (high, low, or no effect), f you were not aware that they had occurred? Explain your answers a. A small amount of unknown adheres to the inside of test tube and did not get dissolved in the cyclohexane b. Some solvent is lost by volatilization. c. The thermometer used in this experiment was miscalibrated to read 0.5°C lower than the actual temperature over its entire scale.Explanation / Answer
The solution to the above problem is as follows.
A. When a small amount of solute (unknown) remained adhered to the inside of the tube. The weight of the solute measured will not be the same as it actually should have been.
delta Tf = i.m.Kf
where,
m = molality = moles/kg of solvent = g of solute/molar mass x kg of solvent
The relationaship of molar mass to weight of the unknown is directly proportional. Hence as the weight taken is less the calculated molaity of solution would be lower. Hence, the molar mass calculated will also turn out to be lower then the actual value.
B. When some solvent is lost by volatilization. The molality of the solution calculated as higher value then the actual value. So the calculated value of molar mass in this case would be higher then the actual value.
C. When the thermometer read 5 oC lower then the actual value. Their will not be any effect on the molar mass of the compound. What we measure here is the difference in the temperature of the initial and the final solution, which would remain the same.
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