I understand that the ability of standard salt solutions commonly used to produce a certain relative humidity (RH) in a closed space changes somewhat with the temperature.
Where do I find data to trust when it comes to RH created by over-saturated solutions of magnesium chloride, magnesium nitrate and cobalt chloride at 15-30 degrees C?
The tables I have found does not cover the whole temperature span in question unfortunately...
Hi!
I attach a page from the handbook for MgCL2 and Mg(NO3)2.
For CoCl2 you can get the required data theoretically, from water activity obtained by PHREEQC modeling.
Michael Zilberbrand thanks a lot for your help!
PHREEQC modeling sounds like something I cannot do. You don't happen to know where to look or whom to contact to find out the data?
I already found the RH from saturated CoCl2 solution from 25 degrees C and up but I still haven't seen any information about temperatures below that.
It is just the values for 10, 15 and 20 degrees C I need.
I tried to compare the measured data for MgCl2 with calculated by PHREEQC. The absolute difference is about 1%. Is it good enough? See below:
Comparison of the results with measured data from Lide D.R. (ed.) Handbook ...
Temperature Calculated Reported
10 32.39 33.47
15 32.27 33.30
20 32.13 33.07
25 31.96 32.78
30 31.75 32.44
Michael Zilberbrand thanks a million for taking your time!
A difference within one percent would be fine and I guess that your thought is that if it fits for magnesium chloride the theoretical calculation would give a reasonable fit for cobalt chloride too?
However, I've been searching a couple of hours for more information regarding cobalt chloride and relative humidity and I finally found values for for 15 and 20 degrees! Unfortunately the RH goes upwards when the temperature goes down (73 % RH at 15 degrees C!) so I cannot use the water/CoCl2 system for my experiment since the purpose was to have 64-66 % RH at all temperatures.
I guess I will order some Boveda Humibags for 65 % RH from some cigar shop and see if they are stable enough over 15-30 degrees C. If that does not work I might use a 35 % H2SO4 solution that seems to be exactly what I need, although I really would have preferred not using acid in this case since spillage could make the samples self ignite (contains potassium chlorate!).
Thanks again!
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