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Topic: hygroscopic concept  (Read 2371 times)

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Offline johnnyjohn993123

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hygroscopic concept
« on: March 16, 2016, 08:50:47 AM »
hi , I was wondering if there is an existing  graphical representation of the increase in mass with time as the independent variable for a hygroscopic substances.. I only see with respect to humidity as the independent variable.

Offline Arkcon

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Re: hygroscopic concept
« Reply #1 on: March 16, 2016, 09:28:29 AM »
Hmmm... perhaps you can determine it experimentally for a fixed mass of sample over time, for a fixed ambient humidity.
Hey, I'm not judging.  I just like to shoot straight.  I'm a man of science.

Offline johnnyjohn993123

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Re: hygroscopic concept
« Reply #2 on: March 16, 2016, 10:10:36 AM »
well thanks! I was considering how the differential model for chemical reaction would occur, where at any given time , there would be some slight changes to a the mass of the salt. It just so happened that its dependent towards humidity and not time (accourding to the internet)  ;D

Offline Arkcon

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Re: hygroscopic concept
« Reply #3 on: March 16, 2016, 10:46:45 AM »
Well, there are other dependencies.  A mass of solid is going to shield the inner mass from moisture.  Even more so, as the mass coats itself with liquid.  At some point, an equilibrium is reached between the concentrated solution surrounding the hygroscopic salt, and the ambient air.

That's why quantitative drying generally specifies a layer of substance no deeper than a millimeter.  Even though that describes the reverse reaction, you see why its important.

So, you've got a controlled mass, in a thin layer that you've defined, you have it on the weigh pan of an analytical balance in a controlled humidity environment.  Then you can plot the gain in weight as a function of time.

The question is why?  If its not important enough for you to do, maybe its not important enough for anyone to do, and there's no table or reference to find the information.  Or maybe you can find a table of values such as you're looking for.
Hey, I'm not judging.  I just like to shoot straight.  I'm a man of science.

Offline Enthalpy

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Re: hygroscopic concept
« Reply #4 on: March 19, 2016, 08:39:40 PM »
In addition to all difficulties that result from inhomogeneity, I suspect that many hygroscopic molecules can bind several water molecules with varied strength - similarly to a polyacid having several pKa - which increase the difficulty of deriving a simple dependance over time.

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