1. Water vapor evaporating from a pond does so as if it were diffusing across an air film 0.15 centimeters thick.  The diffusion coefficient of water vapor in 20 degrees C air is about 0.25 cm2/sec.  If the air out of the film is fifty percent saturated with water vapor, how fast will the water level drop in a day? 
Data: the saturation partial pressure for water vapor at 20 degrees C is 23.4 millibar (1 atm = 1.0325 bar).  The molecular weight of water is 18 g/mol.  Hint: assume the mixture of air and water vapor obeys the ideal gas law.
 
2. Diaphragm cells are frequently calibrated by allowing 1 molar potassium chloride to diffuse into pure water. 
Your cell has compartment volumes of (upper) 42.3 cm3 and (lower) 40.8 cm3; the diaphragm is a glass frit 2.51 cm in diameter and 0.16 cm thick.  In one calibration experiment, the concentration difference at 36 hours 6 minutes is 49.2% of that originally present.
Estimate the diffusion coefficient?  
What is the cell's calibration constant?
Assume H, the membrane partition coefficient=1.

3. Consider the diffusion of dopant element A into crystalline wafer. The dopant rich coating is considered as a large source of A relevant to the amount of A diffused, so that the surface concentration CAs can be considered a constant. Determine the depth (z) of the front of diffusing dopant after two hours of diffusion. Assume that the front concentration is 2% of the surface concentration. Diffusivity of A= 6.5 X 10-13 cm2/s.