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At a high temperature, water is evaporated from the saturated solution by heating. What is the solution losing exactly by the fact that the water left the saturated solution? Does it affect its concentration...solubility?

I have a two thoughts. First, as water evaporated, the amount of dissolved substance 'inside the water' in the solution a.k.a concentration is decreasing. Thus, if the concentration decreased, based on the substance the solution may turn into unsaturated solution.

However, I have another thoughts that water only carries the 'overall' volume of the solution. Meaning, decreasing the amount of water it will decrease the volume of the solution while the amount of substance inside the solution will remain constant, thus, the concentration will increase . These thoughts leaving me a doubt in my understanding.

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  • $\begingroup$ @Poutnik thats why I need someone to confirm this. How? $\endgroup$
    – Panpaka
    Commented Oct 24, 2020 at 8:36
  • $\begingroup$ @Poutnik so that means the water just affecting the total volume of the solution? e.g. if 10 liter of water evaporated from 50 liter saturated solution (after the temperature increased) then the initial volume would be 60 liter? $\endgroup$
    – Panpaka
    Commented Oct 24, 2020 at 9:01
  • $\begingroup$ The answer has been updated. $\endgroup$
    – Poutnik
    Commented Oct 24, 2020 at 9:04

2 Answers 2

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Salts do not precipitate from unsaturated solutions.

When saturated salt solution is being evaporated, water content decreases. The solution keeps being saturated, as while water is evaporating, the excessive amount of salt is precipitating. There is less salt in the solution, because there is less of saturated solution.

10 L of saturated solution does not contain 10 L of water. By other words, evaporating 10 L of the solution does not mean evaporating 10 L of water. If you get data about solubility and density you can easily calculate how much of salt and water is contained in 1 L of the saturated solution.

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  • $\begingroup$ That's actually my main question and I tried to connect the logic from the question I posted here. Let's say again, 10 liter of water evaporated from 50 liter saturated solution (after the temperature increased to T) and the solubility of saturated solution is 20 at that T temperature. What do we know from this? I couldn't relate the evaporated water and the solubility of saturated soln. Does this have a connection to precipitation formed? I apology if I kept bombing you with questions. $\endgroup$
    – Panpaka
    Commented Oct 24, 2020 at 13:14
  • $\begingroup$ Technical note: If you need to clarify an answer, than comment the answer. If you rather clarify and further elaborate your question, modify the question instead. That gives you more space and options to formulate and format the text. $\endgroup$
    – Poutnik
    Commented Oct 24, 2020 at 13:18
  • $\begingroup$ By solubility 20 you mean 20g/100mL water, right? As that is the standard way. Then you need the density of such solution. There is many data pages or online calculators to do so.Then from this density and density of the solid salts you can calculate, how much of water evaporated and how much of salt precipitated if the total volume decreased by a given values. The key here is law of mass conservation. Law of volume conservation does not exist. $\endgroup$
    – Poutnik
    Commented Oct 24, 2020 at 13:21
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When water is evaporated from a solution, the water molecules leave the solution so there are more molecules if the substance left in the solution, so therefore overall the amount of water decreases from the solution and hence there are more substance molecules dissolved than water molecules in comparison to the solution prior to hearing and as the amount of substance increases relatively,the concentration of the substance increases in the solution

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