gchem question

[gabrielmeraz]

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Hi guys, this is an Osmotic Pressure question
-If you have a solution of 1L of H20 and 234 grams of NaCl, what is the Osmotic Pressure at STP (R=0.1atm/mol K)?

Well, the formula is P=M(for molarity)*R*T
If I plug in the values I get 109.2 (when using 273K as my standard Temperature). When I use 298 for my standard temp I get 119.2. None of those answers are correct. Topscore has 218.4 atm as the right answer. I don't understand why? I guess my questions is when should I use 273K as my standard temp and when 298K as my standard temp. In addition, why in the world is the answer 218.4K???? 😕

 

[DrTacoElf]

Hi guys, this is an Osmotic Pressure question
-If you have a solution of 1L of H20 and 234 grams of NaCl, what is the Osmotic Pressure at STP (R=0.1atm/mol K)?

Well, the formula is P=M(for molarity)*R*T
If I plug in the values I get 109.2 (when using 273K as my standard Temperature). When I use 298 for my standard temp I get 119.2. None of those answers are correct. Topscore has 218.4 atm as the right answer. I don't understand why? I guess my questions is when should I use 273K as my standard temp and when 298K as my standard temp. In addition, why in the world is the answer 218.4K???? 😕

Great question!

NaCl dissociates (Na+ and Cl-) to give 2X molar of what you would expect. Thus if you have 1M NaCl it will effectively be 2M. This same rule applies for all strong electrolytes. Try that 🙂

P=MRT is the correct formula to use.

 

[luder98]

Great question!

NaCl dissociates (Na+ and Cl-) to give 2X molar of what you would expect. Thus if you have 1M NaCl it will effectively be 2M. This same rule applies for all strong electrolytes. Try that 🙂

P=MRT is the correct formula to use.

I want to add one thing. This is from my professor when I asked him this question. He said, even with strong electrolytes, if you have a concentrated solvent, they will not completely dissociate as you expect. Then he gave me a list of several books to read more!

Fortunately, we only deal with dilute solution. So, it's safe to multiply by the number of ions that the compound dissociates into.