[freshman89]

Hi guys,

I recently had a lab practical lesson that involved determining the enthalpy and entropy change for the dissolution of potassium hydrogen tartrate, a sparingly soluble salt in water. I obtained a graph of ln K (titrated against NaOH to obtain [K+] and [hydrogen tartrate ion] to calculate Ksp) vs 1/T (4 different temperatures) where the slope of the graph is standard enthalpy change/R and the y intercept is standard entropy change/R. Both the values of enthalpy change and entropy change are positive. (R = ideal gas constant)   

After calculating delta G, I realized that the dissolution is non spontaneous at all 4 temperatures. How do I explain the fact that some dissolution did occur (otherwise titration wouldn't work) even though the dissolution is non spontaneous? Is there some sort of coupling mechanism involved in some way that allows the dissolution to proceed?

Thanks

[DevaDevil]

a potassium salt that does not spontaneously dissolve in water?

even more, tartrate (tartronic acid) is a buffer and dissolves readily in water as well.

Are you sure of your calculations concerning it's (non-)spontaneous dissolution?