If you had two solutions, for example, 100 ml each of 0.5 M $\ce{RbCl}$ and 0.5 M $\ce{NaBr}$, at 20 °C, where the salts have very similar solubility in water, and you mixed the solutions, and allowed the water to evaporate. Would you theoretically end up with equal number of moles of $\ce{RbCl}$, $\ce{RbBr}$, $\ce{NaCl}$, $\ce{NaBr}$? If not, is there an equation or methodology you can use to determine how much of each salt you'd end up with?

  • $\begingroup$ I would be looking at the free energies of formation and work it out from there. The presence of water is a red herring in the crystallization question. $\endgroup$ – Jon Custer Feb 21 '16 at 2:30
  • $\begingroup$ You would end up with an equimolar mixture of all four salts if they all would have exactly the same solubility, which just can't be so. In reality, some salt would reach its solubility limit before the others, and would start to crystallize. Then the concentration of its ions would stay the same, but the other two would continue to grow until something else happens. So it goes. Oh, and then there is a possibility of solid solutions which makes the whole story a lot more complicated. $\endgroup$ – Ivan Neretin Feb 21 '16 at 6:50
  • $\begingroup$ Not only solubility is important, but crystal structure as well: due to differences in ionic radius, the crystals of one salt may exclude those of another. $\endgroup$ – DrMoishe Pippik Feb 21 '16 at 23:07

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