1

Let's say I have a satuated solution of two salts with a common ion e.g. KCl and KI, and they're at mutual saturation (let's say there are 75% by weight KCl/ 25% KI). If I slowly evaporate some water, which salt will precipitate first? What if there are 25% KCl instead? More generally, how to predict which salt will drop out of solution first?

R. Wang
  • 219
  • 2
  • 3
  • 2
    Mutual saturation is not a thing. If one salt reaches its solubility product, it will precipitate. If another does, it will. If both do, both will. – Ivan Neretin May 02 '20 at 16:23
  • This question is unsolvable at this stage. For example, you said your saturated solution consists of 75% $\ce{KCl}$ by weight. Is that mean $\pu{75g}$ of $\ce{KCl}$ in $\pu{100g}$ of solution? If so, it is impossible. Maximum solubility of $\ce{KCl}$ in water cannot exceed 25.5% at $\pu{20 ^\circ C}$. That's right, you forgot to include temperature. Solubilities are highly depend on temperature of the solution. – Mathew Mahindaratne May 02 '20 at 16:25
  • Good question would be this type: https://chemistry.stackexchange.com/questions/72700/can-other-substances-be-dissolved-in-a-saturated-solution. You can learn about a thing or two of solubility in those answers. – Mathew Mahindaratne May 02 '20 at 16:28
  • @MathewMahindaratne I could have been clearer, I mean weight of KCl : weight of KI is 75% : 25% – R. Wang May 02 '20 at 16:40
  • @IvanNeretin My bad on mutual satuation. I'm aware of Ksp, and I mean the concentration of both solutes at which one is at its satuation. Mutual satuation is a thing tho, and can be estimated from Ksp. For KI/KCl it should probably be 7.43M/2.14 M – R. Wang May 02 '20 at 17:11
  • I guess I answered my own question lol. thanks all! – R. Wang May 02 '20 at 17:12
  • 1
    Do not forget there is a common ion effect here as well. – Mathew Mahindaratne May 02 '20 at 18:30
  • A saturated solution of a mixture of the two salts would have such a large ionic strength that the notion of the Ksp being a constant just doesn't work, even using activities. – MaxW May 02 '20 at 19:08

0 Answers0