Though this might sound easy, I have been trying to get isotherm data of water-NaCl system but did not have luck. I would appreciate if one can direct me to a suitable source.
The vapour pressure of aqueous NaCl is given by p = p0*exp(-2*Mw*gamma*Cm), where p0 is the vapour pressure of the pure water, Mw is molar mass of water, Cm is the molal concentration of NaCl, gamma is osmolality coefficient (gamma*Cm is osmolality). Every book on electrolytes has gamma tabulated as function of Cm at various temperatures - check e.g. Robinson & Stokes, or google a paper (there are zillions, e.g., http://www.publish.csiro.au/ch/CH9672017). Above 80 deg C, use fugacity instead of pressure, f = f0*exp(-2*Mw*gamma*Cm), if you need it accurate.
You are looking for vapor pressure as a function of T and NaCl-concentration? Look here:
Clarke, E.C.W. und Glew, D.N.: Evaluation of the thermodynamic functions for aqueous sodium chloride from equilibrium and calorimetric measurements below 154°C. ISSN 0047-2689, Journal of Physical and Chemical Reference Data, 14, S. 489-610, 1985.
For RG discussion on the vapour pressure over an oversaturated NaCl solution:
https://www.researchgate.net/post/What-is-the-vapor-pressure-of-an-oversaturated-NaCl-solution
For another related RG query ― yet restricted to cold NaCl aq. sol. ― please check: https://www.researchgate.net/post/Sodium_chloride_solution_saturated_vapor_pressure_at_sub_zero_temperature
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