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Question

What is the most cost effective way to prepare saturated solutions of each of these compounds? LiCl, K2CO3, and NaCl.

Background

I am trying to create a rudimentary controlled humidity device within my lab. I am essentially taking a desiccator, removing the desiccant, cleaning thoroughly, and inserting various saturated salt solutions in order to have a controlled vapor pressure of water above the surface of the saturated solution; assuming there is a constant temperature.

I have included a temporary link to the two journal articles I am using to try and accomplish this goal, but I will try and give all the relevant information here as well so people don't have to go and check out my shadylinks.Dropbox w/ journal articles

I have the salts needed to make up solutions of LiCl, K2CO3, and NaCl. They were quite expensive for our small research group though and I don't want to waste any materials. The volume in the bottom of the desiccator is about 200mL and I have 100g of each salt to use for the course of the short experiment.

I know that a saturated solution in general chemistry is simply prepared by dissolving as much salt as is possible into a heated solution and then cooling it. However, as I have been reading some of these papers there are many reports of non-diffusing barrier layers on the surface of many saturated salt solutions. This means that the relative humidity of these solutions changes a significant amount over time. Some papers report the use of "slurries" or "sludges" in which just enough water is added to a pile of salt in order to make it appear damp.

I have also read that the preparation of a saturated salt solution is very dependent on the relative humidity which is established by that salt solution. More specifically, that low rel. humidity saturated solutions might need the slurry approach and higher rel. humidity solutions favor the standard saturation techniques. However, I have no idea what the cuttoff for "low" and "high" is and I am left to assume it's whatever the atmospheric humidity is.

I am more than happy to do the legwork and read up on as much as need be, and I am still doing so as this post sits. I just don't know where to go or how to approach the question of how much saturated solution, or how much slurry, will be enough to control the humidity inside of about a 1L container. I can't afford really to go about preparing the solutions in order to find the best method experimentally and I was really hoping there were some experienced people out there who could point me in the right direction.

Thank you for all of your time reading this regardless of response! It is much appreciated!

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  • $\begingroup$ I would go by simply adding while stirring until a solid remains. Then a little more. The temperature in the lab should be stable enough (presumably) not to alter Kps. Just check that no more salt dissolve, I.e. take a periodic look at the solid deposit at the bottom. That is. $\endgroup$ – Alchimista Dec 13 '18 at 12:27
  • $\begingroup$ "Some papers report the use of "slurries" or "sludges" in which just enough water is added to a pile of salt in order to JUST make it appear CLEARLY damp," adding water drop by drop uniformily (personal experience). $\endgroup$ – Fernando Dec 16 '18 at 22:35
  • $\begingroup$ I went through and tried to calculate how much water vapor I would need to fill the chamber, then added that much water to a slurry pile which was large enough to not dissolve when that much water was added. However, I am getting some pretty erroneous results with my K2CO3 samples. I am currently still trying to find out what could be going on here. $\endgroup$ – hotmaildotcom1 Apr 15 at 19:20
  • $\begingroup$ Thanks for all the help everyone. Sorry for the delay in response. $\endgroup$ – hotmaildotcom1 Apr 15 at 19:21

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