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?
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2$\begingroup$ 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. $\endgroup$– Ivan NeretinCommented May 2, 2020 at 16:23
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$\begingroup$ 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. $\endgroup$– Mathew MahindaratneCommented May 2, 2020 at 16:25
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$\begingroup$ Good question would be this type: chemistry.stackexchange.com/questions/72700/…. You can learn about a thing or two of solubility in those answers. $\endgroup$– Mathew MahindaratneCommented May 2, 2020 at 16:28
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$\begingroup$ @MathewMahindaratne I could have been clearer, I mean weight of KCl : weight of KI is 75% : 25% $\endgroup$– R. WangCommented May 2, 2020 at 16:40
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1$\begingroup$ Do not forget there is a common ion effect here as well. $\endgroup$– Mathew MahindaratneCommented May 2, 2020 at 18:30
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