RogueRose
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Most hydrophilic: MgO, CaCl2, Cu(NO3)2, Ca(NO3)2, CuSO4, NH4NO3 - Very interesting Results!!
Well, I didn't really think there would be any question about which of these would absorb atmospheric water faster but the results are astounding,
IMO.
Just to make sure we are all on the same page with what hydrate level and purity I'm talking about, here is the list of the products:
MgO - Side walk deicer
CaCl2 - Side walk deicer (says 77& but that means that about 20-23% is water - so it's a hydrate already)
Ca(NO3)2 - fertilizer - hydrated
NH4NO3 - Fairly pure powder - probably close to 98-99+%
Cu(NO3)2 - very pure 99+% - very blue crystals (looks basically like the sulfate)
CuSO4.5H2O - 99+% pure - pentahydrate
After a year of sitting exposed to the elements in the same setting, the MgO is a solid brick and is dripping a MgO solution while the CaCl2 is
somewhat caked together on the top of the container while the bottom 80% is still the same as it was before.
The Cal Nit has changed slightly by caking at the top 5-8% while the rest remain the same.
I've seen no change at all in the CuSO4, Cu(NO3)2 of NH4NO3. I was very surprised at these as I expected some absorption of liquid and maybe there
has been but not enough to pool any liquid in the container.
The MgO has almost doubled in weight while the CaCl2 is only about 10% heavier. I would never have thought this and I'm trying to figure out how
the MgO is absorbing so much water and if it is forming a hydrate then a solution?? I havent' been able to find a MgO hydrate so this is a little
confusing.
Anyone have any idea as to why I'm getting this result and how the MgO is absorbing so much?
I'd like to try this with anhydrous CaCl2 and CuSO4 and then do a weight test to see which absorbs more.
Also, when people talk about the strength of a dessicant, are they talking about "how much they can absorb" as in quantity, or how strong the pull is
such as being able to pull the last 2-3% of moisture out of the air where other dessicants can't do it.
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DraconicAcid
International Hazard
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Your MgO isn't forming a hydrate- it's forming a hydroxide first. MgO + H2O --> Mg(OH)2 Magnesium oxide and hydrixide aren't very soluble, so I'm
surprised that it's forming a solution.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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feacetech
Hazard to Others
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https://en.wikipedia.org/wiki/Critical_relative_humidity
is a helpful parameter
however contaiminats can quickly change this usually for the worse
Calcined magnasite MgO and Burnt lime CaO are a bitch if you get the dust on the back of your sweaty neck
as above forms a hydroxide and genrates heat when water is added
aformention hot hydroxide + skin = ouch
[Edited on 8-9-2017 by feacetech]
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Magpie
lab constructor
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Mood: Chemistry: the subtle science.
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When I worked we had a LUWA vertical dryer with a rotor that wiped the inside surface and the powder fell to a vapor locked outlet for disposal. The
steam jacket was kept at about 365 deg F. Mg(NO3)2 would not dry. So we pre-treated the feed with NaOH to convert it to insoluble Mg(OH)2 which
would dry to a powder.
[Edited on 8-9-2017 by Magpie]
[Edited on 8-9-2017 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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AJKOER
Radically Dubious
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The MgO may do more than just form Mg(OH)2. If sunlight is a factor in exposure to the elements, note that MgO is also photoactive, but not to the
extent of say TiO2.
In the presence of impurities, more chemistry could be occurring, adding to the mass of the MgO!
[Edited on 9-9-2017 by AJKOER]
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clearly_not_atara
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MgO also absorbs CO2 from the air over time. This adds more weight than water. Copper nitrate is volatile when anhydrous isn't it? IIRC it can only be
prepared in a hydrogen-free protocol (Cu + N2O5 or similar)
[Edited on 9-9-2017 by clearly_not_atara]
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kmno4
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Funny (or sad) thing, how many "chemists" here uncritically discuss this MgO....
Besides, this is one of the most stupid topics in this year.
Слава Україні !
Героям слава !
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