The molar mass to a solid as determined by freezing point depression is 10% high

Question

The molar mass to a solid as determined by freezing point depression is 10% higher than the true molar mass Which of the following experimental errors could not account for this discrepancy'? Select one. Before the solution was prepared, the container was rinsed with solvent and not dried Some solid was left on the weighing paper Not all the solid was dissolved More than the recorded amount of solvent was pipetted into the solution the solid dissociated slightly into two panicles when it dissolved

Explanation / Answer

dTfp = Kf x m x i
dTfp = Kf x ((mass solute / mw solute) / kg solvent) x i

a) if some of the solid was not dissolved, your actual mass solute value would be too HIGH. This would make molar mass too HIGH.
b) if kg of solvent was too low (the recorded # < actual), this would make the molar mass calculation too HIGH.
c) if you assume i = 1 but some dissociation occured making i > 1, then your value for i would be too LOW and this would make molar mass to LOW
d) your value for mass of solute would be too high and this would make molar mass too HIGH
e) your value for kg solvent would be too low and this would make molar mass too HIGH

answer is C

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