IS this Correct?

[urDDS]

Advertisement - Members don't see this ad

if you have a sol'n 1 L h20, 234g NaCl,find osmotic pressure?

they worked it out and got moles =4, but they said it will dissociate into
4Na+4Cl= 8, i thought that NaCl have i=2

 

[whateveryoulike]

if you have a sol'n 1 L h20, 234g NaCl,find osmotic pressure?

they worked it out and got moles =4, but they said it will dissociate into
4Na+4Cl= 8, i thought that NaCl have i=2

you have a total of 4 moles of NaCl. osmotic pressure is concerned with the number of moles TOTAL regardless of what the individual molecules are. since NaCl dissociates completely in water, you have 4 moles of Na and 4 moles of Cl, making a total of 8 moles worth of molecules.

the osmotic pressure equation is just a derivation of the ideal gas law (regardless of the fact that its used for liquids and not gases). you know that PV=nRT and you know that solution concentration is n/V so...

P=(n/V)RT ---> P=cRT

and remember that P (pressure) can be considered osmotic pressure.

if you remember ideal gas law, you should know that theyre not concerned with individual molecules, just the total number of them. once again, NaCl dissociates (aka the normality is double whatever the mole number of NaCl is)

 

[HowAboutDAT]

didnt they have to provide a temperature?

 

[whateveryoulike]

didnt they have to provide a temperature?

i was wondering the same thing but just assumed he didnt provide it since the wording of his question seemed abbreviated anyway

 

[urDDS]

i was wondering the same thing but just assumed he didnt provide it since the wording of his question seemed abbreviated anyway

no temp was provided

 

[BaylorDDS]

was it run at standard conditions?

 

[whateveryoulike]

no temp was provided

you need temp to calculate osmotic pressure. not sure where the question passage came from but did it have a generalized list of conditions for a series of questions maybe? which would explain why they didnt give it to you in the specific question.