Hi all,
Is the rate of dissolution of salts in water directly related to their solubility?
The solubility of NaCl and KCl in 300C are 36 and 34, respectively. If 1 liter of water is added to 1 kg of a mixture of these two salts (NaCl:10 %w.t, KCl: 90 %w.t), how will the liquid and new solid composition after the dissolution?
In other words, how is the equilibrium composition of the solution estimated in this case?
Factors affecting in-vitro dissolution rates of solids in liquids are: surface area of undissolved solid, saturated solubility (Cs) of solid in dissolution medium, concentration of solute (C) in solution at time t, dissolution rate constant and thickness of boundary layer (Noyes–Whitney equation). Rate of dissolution increases proportionally with increasing difference between CS and C. Thus high CS speeds up dissolution rate).
Please note that solubilities for both NaCl and KCl salts in their joint/mixed aq. solutions can be predicted after those for each single salt saturated solution, which presumably, are more readily available:
i) Being SKCl the solubility for KCl given in terms of molarity for its single salt saturated solution, KspKCl = [K+]*·[Cl-]* = SKCl2; where C*KCl = [K+]* = [Cl-]* = SKCl. Here C stands for formality and saturation is denoted by *.
ii) Simillarly, for a NaCl single salt saturated solution: KspNaCl = [Na+]*·[Cl-]* = SNaCl2; where C*NaCl = [Na+]* = [Cl-]* = SNaCl.
iii) KspKCl and KspNaCl can also be accepted to apply to the joint salt solution, but, in this case, the common ion effect should be accounted for.
iv) The solubility of each salt in the joint salts solution, also given in terms of molarity (here denoted by S†NaCl and S†KCl), can be predicted considering that for saturated joint salt solutions we should have: KspKCl = [K+]*·[Cl-]* = S†KCl·[Cl-]* ; KspNaCl = [Na+]*·[Cl-]* = S†NaCl·[Cl-]*; where [Cl-]* = S†NaCl + S†KCl ≡ S†.
v) Hence: S†KCl = KspKCl/S† and S†NaCl = KspNaCl/S†; from which each salt (interdependent) solubilies can be predicted for their joint solution.
vi) We can arbitrarily fix the concentration of one salt below its saturation limit for its single solution, to then predict the solubility of the other salt in that joint solution.
vii) Both salts are strong electrolytes, so that they can be taken as completely dissociated.
viii) For this kind of prediction, the available solubility data must often be first converted for M ≡ mol/dm3 (solute : solution) units.
ix) Experimental data is directly available for some joint salts saturated solutions. You may alternatively/complementarily search for such data in the literature.
x) Activity coefficients (and related ionic strength effect) were not ― but can be ― accounted for.
Perhaps of some interest to this query: https://www.researchgate.net/post/How_to_create_multicomponent_fixed_quantity_solution_of_inorganic_salts
- Badges
- Science topic