[Excelsius]

I would appreciate if someone could explain to me where I can find information on the efficiency of dissociation between certain compounds. I am trying to calculate the osmolarity of this compound:

Content:
NaCl
KCl
NaH2PO4*H2O
D(+) Glucose
NaHCO3
MgCl2*6H2O
CaCl2*2H2O

MW: (respectively as above, waters of hydration also taken into account)
58.44
74.55
137.99
180.16
84.01
203.30
147.02

mM: (respectively as above)
124.00
3.50
1.25
10.00
26.00
2.00
2.00

I come up with a theoretical molarity of 0.169 and osmolarity of 0.3315 Osm. The problem is that when I measure the actual osmolarity of this solution, I get around 0.304 Osm. I think that this is perhaps due to the incomplete dissociation of the particles in H2O. For example, NaCl = 2x, but in reality, maybe it's less than that. Can anyone shed light on this and whether the exact dissociation values have been measured?

Thank you.

[Borek]

This is about ion association (creation of ion pairs). As far as I know measurement is the safest (and the most correct) approach, as these things are very difficult to calculate, especially in the high ionic strength solutions.

[Excelsius]

This is about ion association (creation of ion pairs). As far as I know measurement is the safest (and the most correct) approach, as these things are very difficult to calculate, especially in the high ionic strength solutions.

I would still like to know as to how the calculations are supposed to be done. Some specifics though:

1. Most of the osmolarity is contributed by NaCl and bicarbonate. Both are one of the most common compounds. I think that these compounds must have been thoroughly studied and the data must be available somewhere. After some further reading, I found out that what I need is the osmotic coefficient, which is the multiplier that indicates the percentage of dissociation. Can you point me to graphs or tables that show the osmotic coefficient of these two compounds at various molarities?

2. Assuming that the osmotic coefficients haven't been thoroughly calculated for these compounds, which I do not believe, what would be the experimental method of doing this? Creating NaCl concentration of certain value and then measuring with osmometer to come up with the coefficient?