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I have to use dilute salt solutions incredibly frequently, and it takes valuable time to make them from pure reagents every time I need them.

Are concentrated salt solutions fairly stable over time? Does anyone know of any papers describing their ability to maintain static concentrations for long periods?

Edit:

To qualify, I am curious about a wide range of salts. NaCl, ammonium chloride, magnesium sulfate, calcium chloride, potassium phosphate etc...

I am also not especially concerned about analytical precision for my use, but understanding how this could be affected might be useful to others.

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    $\begingroup$ Do you mean 'table salt solutions' ? $\endgroup$ – permeakra Jul 15 '15 at 16:31
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    $\begingroup$ If you mean sodium chloride in water, I don't think chemical stability is your problem, but rather analytical precision. Contamination and solvent evaporation could throw off your measurements, for example. $\endgroup$ – Nicolau Saker Neto Jul 15 '15 at 16:33
  • $\begingroup$ Can we mark this as "homework"? The question lacks any display of own thought. $\endgroup$ – Karl May 25 '16 at 21:07
  • $\begingroup$ Mark it however you wish. I have my own thoughts about the issue, but I felt sharing them would have guided answers towards my own confirmed suspicions rather than being objective. $\endgroup$ – Eli Riekeberg Jun 20 '16 at 20:04
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Salt solutions generally do not spontaneously change in concentration. However, there are a few factors that could influence this: the first one is that the solvent (water, for example) could evaporate, increasing the concentration of the salt. You can prevent this by sealing your containers. The second one is that, as the temperature decreases, salts could crystallise out of the solution. However, this can be easily fixed by re-warming the solution.

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    $\begingroup$ There is more to it than that. Some salts would slowly hydrolyze over time. Some would react with oxygen or other components of air. Some would just up and decompose, even in a sealed container. Some (though none of the mentioned in the question, which are all inorganic) can even support primitive life. $\endgroup$ – Ivan Neretin Mar 26 '16 at 18:54

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