A laboratory technician wishes to separate a mixture of crystalline iodine (I2) and sodium chloride (NaCl) using a vacuum sublimation apparatus that can maintain a pressure of 1.0torr inside the chamber. The following partial vapor-pressure data for iodine are available:
Temperature (K)
Vapor pressure of I2 (torr)
298
0.30
338
5.0
The vapor pressure of solid NaCl is negligible (≪10−9torr) below its melting point.
(a) Describe, in a logically ordered series of steps, a procedure that would allow collection of purified iodine while leaving sodium chloride behind. Include details regarding pressure control, temperature adjustment, and product recovery.
(b) Explain, at the particulate level, why sodium chloride remains in the solid phase under the stated conditions while iodine does not.
(c) Using the vapor-pressure data, estimate the minimum temperature (to the nearest 5 K) required for iodine to sublime at 1.0torr inside the apparatus. Clearly show the quantitative reasoning leading to your estimate.
(d) Identify one practical limitation or safety concern associated with the proposed sublimation procedure and propose a viable modification to mitigate the issue.