Freezing Point Depression Lab Objective: To use freezing point to determine the

Question

Freezing Point Depression Lab

Objective: To use freezing point to determine the molecular weight of an unknown substance.

In this lab, we used benzophene as the solvent, which has a freezing point of 48.1 degrees celsius and Kf value of 9.80 degrees C/m. The procedure consisted of measuring out 10 g benzophenone in a test tube and melting the substance in a warm water bath. When melted, we removed the test tube from the bath and allowed it to cool. We observed the freezing point. Next, we added half a gram of an unknown substance to the test tube and melted the soultion once more. We observed the freezing point.

So, how would the experiment be different if an ionic compound were used? What would have to be done differently in the data workup to account for this difference?

Explanation / Answer

If ionic compound were used , then the observed freezing would be lower than the normal freezing point of the solution. Then experimental molar mass would be less than normal molar mass. This is due to dissociation nature of solute.

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