Student Doctor Network Forums Colligative properties...
 Register FAQ SDN Live Mark Forums Read

 MCAT Study Question Q&A Subforum specifically for asking questions when studying for the MCAT. Please no actual MCAT questions. RSS:

 06-15-2012, 11:34 PM #1 Senior Member   Join Date: Sep 2009 Posts: 534 Colligative properties... SDN Members don't see this ad. (About Ads) A semipermeable membrane separates an aqueous solution of 0.003 M NaCl from an aqueous solution of 0.0025 M BaF2. With this apparatus, one would observe that water crosses the membrane: A. from the BaF2 solution to dilute the NaCl solution. B. from the NaCl solution to dilute the BaF2 solution. Correct Answer C. from the BaF2 solution to concentrate the NaCl solution. D. from the NaCl solution to concentrate the BaF2 solution. Explanation: B. Osmotic pressure is a colligative property, which means it depends only on the concentration of solute particles, and not their identity. Therefore, a 0.003 M solution of NaCl will have an effective molality of 0.006 M (since NaCl is composed of two ions) and a 0.0025 M solution of BaF2 will have an effective molality of 0.0075 M (since BaF2 is composed of three ions). Osmotic pressure will drive movement of water from the lower concentration solution (NaCl) to the higher concentration solution (BaF2). Note that this movement of water acts to dilute the BaF2 solution. I think their answer is wrong...and I think this explanation support my answer...Am I correct?
06-15-2012, 11:51 PM   #2
Banned

Status: Pre-Podiatry
MDApps: View Profile
Join Date: Dec 2011
Posts: 18,777

Quote:
 Originally Posted by BestDoctorEver A semipermeable membrane separates an aqueous solution of 0.003 M NaCl from an aqueous solution of 0.0025 M BaF2. With this apparatus, one would observe that water crosses the membrane: A. from the BaF2 solution to dilute the NaCl solution. B. from the NaCl solution to dilute the BaF2 solution. Correct Answer C. from the BaF2 solution to concentrate the NaCl solution. D. from the NaCl solution to concentrate the BaF2 solution. Explanation: B. Osmotic pressure is a colligative property, which means it depends only on the concentration of solute particles, and not their identity. Therefore, a 0.003 M solution of NaCl will have an effective molality of 0.006 M (since NaCl is composed of two ions) and a 0.0025 M solution of BaF2 will have an effective molality of 0.0075 M (since BaF2 is composed of three ions). Osmotic pressure will drive movement of water from the lower concentration solution (NaCl) to the higher concentration solution (BaF2). Note that this movement of water acts to dilute the BaF2 solution. I think their answer is wrong...and I think this explanation support my answer...Am I correct?
B is correct and the explanation supports answer B.

06-16-2012, 12:04 AM   #3
Senior Member

Join Date: Sep 2009
Posts: 534

Quote:
 Originally Posted by MedPR B is correct and the explanation supports answer B.
Sorry...My gosh...did not read carefully the answer...I hate that. I thought B said: (from the NaCl solution to the diluted BaF2 solution)

 Bookmarks

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is Off Forum Rules