Physichal chemistry ideal solutions

[demander]

how can we without any calculation see if a solutions is ideal or non ideal?
for exemple if you are given a sort of values for pressure and for each the vapour and liquid composition of a mixture
how can we say if there is a ideal or non ideal solution?
i'm getting crazy with this cause normally when i saw something about ideal solutions i always see some calculations, so how can i, only looking to values as i said above, say if a solution is non ideal or ideal?
can be seen by dispertion of values? conjugation of values?
how?

maybe for some this question is too easy but after a week of electrochemistry i really have my brain stuck :S and i can't answer this.

i didn't put this on homework section cause my main problem is the theory behind this, but if you see this is in the wrong section be free to move.

 

[GCT]

One can assess a solutions ideality by calculating the excess molar volume due to adding two liquids for instance ethanol and water ; one way of finding out the excess molar volume is through a method involving refractive index measurements and some data plotting. I can describe this method subsequently if needed.

 

[demander]

for example giving the table in attachment with the values where x is the liquid compound and y the vapour compound of the same solution how can i say that the solution is non ideal without calculations? can a diagram be usefull in that situation? and if you can please explain that method you talk before

 

[GCT]

Alright you want to utilize Raoult's law for the diagram - it really depends on what "P" is - is it the total P? Assuming that the parameter for x and y is mole fraction it seems that the solution itself is non-deal since both the mole fraction of the vapor P and the vapor P itself is not linear with respect to its relationship with the mole fraction in the solution - regardless you need to inform me on what P actually is as well as the other parameters in the solution.

 

[demander]

x and y are exactly what you said mole fraction of each component( liquid (x) vapour (y)
P is the vapour pressure of the diferent compositions of liquid and gas
of a mixture of ethanol + chlorofom at 45ºC (318,15K), don't know if this last line matters for it or not but i put it to complete the information

hope i have said what i want, sorry for my english a bit confusing :S

 

[GCT]

So the P is the vapor pressure of both ethanol and chloroform? Irregardless use Raoult's equation to construct a diagram of the mole fraction of the analyte on the x-axis and the vapor P of that analyte on the y-axis - you should observe a straight line. The line should be linear; any kind of curvature indicates non ideality.

 

[demander]

ok thanks very much for the help, was really really usefull

 

[demander]

by the way connected with this same question what is in fact the(or an) azeotropic point? i see in many places but was all a bit confusing seem that is the pressure at what the boiling doesn't change anything... but how can this be aplied to activity coeficients
?

 

[GCT]

http://en.wikipedia.org/wiki/Azeotrope#Deviation_from_Raoult.27s_law

Azeotropes don't obey Raoult's law - this should give you a hint with respect to the AC. I'm going to give some more details I'm a bit busy at this time.