<p>Seems like there's a lot of these. Anyways.... from the 1994 chem test:</p>
<p>As shown in the figure above, two compartments are
separated by a porous membrane that is permeable to
ionic salts. A sodium chloride solution is placed in one
compartment while distilled water is placed in the other.
Factors that influence the initial rate at which the water
diffuses into the compartment containing the NaCl
solution include which of the following? </p>
<p>I. Concentration of the sodium chloride solution
II. Area of the porous membrane
III. Temperature of the system</p>
<p>The answer is all 3. Why? Shouldn't it just be II and III. The concentration of NaCl would just change the rate of diffusion out of the NaCl solution or the net change in the rate not the initial rate water diffuses into the compartment. Am I interpreting this wrong?</p>
<p>Depending on how you read the question, there are many different combinations of possible answers. However, the question is dealing with the initial NET rate of diffusion. Many of the water molecules on the salty side are bound up in hydration shells around the sodium and chloride ions, and are unable to be part of the diffusion. The more solute, the fewer “free” water molecules on the salt side, and the higher net rate of diffusion of water from the salt-free side. As time goes on, and salt ions diffuse across the membrane, the two sides will eventually have an equal distribute of solute. That is why the question is asking for the the initial rate.</p>
<p>The question is asking about Osmotic Pressure, which is a colligative property, so the concentration of the NaCl would also affect the rate of diffusion.</p>