2. A student, following the procedure described in this module, used water as th

Question

2. A student, following the procedure described in this module, used water as the solvent and encountered some interesting problems. Comment on the effect, if any, each of the following situ- ations could have had on the experimental results. 0) The unknown, a white powder, failed to dissolve in the solvent. (2) The student returned to the laboratory in structor for a different solid unknown. This unknown dissolved, but bubbles were seen escaping from the solution almost immediately after the addition of the solid. (3) As the student was setting up the apparatus to measure the freezing point of the unknown solution, the thermometer assembly rolled off the laboratory bench, and the thermometer broke. The student obtained a new thermometer and performed the experiment as instructed. 191

Explanation / Answer

Kf is the cryoscopic constant which is dependent on the properties of solvent and not solute. Presence of solute in solvent decreases the freezing point of solution, this is called as freezing point depression.

Presence of salts and impurities in tap water will decrease its freezing point so the kf value of t - butyl alcohol will also be affected.

Delta Tf = i kf m

So if freezing point depression increases, magnitude of kf will also inrease.

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