Sciencemadness Discussion Board - Dimorphism of Calcium Acetate


	Not logged in [Login ]

FAQ

Member List

Today's Posts Forum Stats

Stats

Back to:

Sciencemadness Discussion Board » Fundamentals » Chemistry in General » Dimorphism of Calcium Acetate

Printable Version

SnailsAttack

Hazard to Others

Posts: 166
Registered: 7-2-2022
Location: The bottom of Lake Ontario
Member Is Offline

posted on 2-3-2022 at 00:47

Dimorphism of Calcium Acetate

In the past few months I've recrystallized a lot of calcium acetate, whether it's from eggshells or seashells, or rocks (my new preferred source because they don't smell). And what I noticed is that it evaporates to form 2 very distinct crystals, which I've designated as the alpha and beta variants.

[1]

Calcium Acetate Alpha (CaAc α)
- puffy, almost like popcorn.
- fluoresces under ultraviolet light.
- tends to absorb impurities in the brine, causing discoloration.

Calcium Acetate Beta (CaAc β)
- forms spiny, needle-like crystals, sometimes growing freely or else entrapped in larger masses.
- exhibits no fluorescence
- tends to eject impurities in the brine, resulting in very pure white crystals.

[1] [2]
Calcium acetate alpha often possesses geode-like cavities of the beta morph. I'm not really sure how it generates these hollow shells, maybe through some sort of weird capillary pumping mechanism like the way that saltwater climbs the edge of a glass as it evaporates.

[1] [2] [3]
In these images you can see radial patterns in the beta morph. In the larger of the two "craters" there's a big cluster of the alpha morph growing right in the center.

The criss-crossing interwoven spikes of the beta morph remind me a lot of rapidly-crystallized solutions of supersaturated sodium acetate.

[1]
A high-purity sample so you can see how both polymorphs are normally white.

[1] [2]

When viewed under ultraviolet light, the alpha morph fluoresces while the beta morph does not. I have no idea how this happens and it was the main reason I was absolutely convinced they must be two different chemicals.

This conviction was broken when I tried to isolate the two materials, but found that no matter how many times I separated and recrystallized them I always ended up with dishes containing both crystals.

I also tested if it could've been magnesium acetate, which I made from epsom salt, but I found that magnesium acetate doesn't crystallize, it just turns to goop in a similar fashion to nickel acetate.

--

The conditions under which the crystal structures diverge is unclear but has something to do with the water level of the evaporation dish. Other determining factors such as temperature and impurities are unknown. Further testing required.

clearly_not_atara

International Hazard

Posts: 2799
Registered: 3-11-2013
Member Is Offline

Mood: Big

posted on 3-3-2022 at 09:17

Is it possible that one of them is Ca(OAc)2*xH2O and another is Ca(OAc)2*yH2O*zHOAc?

Quote: Originally posted by bnull

you can always buy new equipment but can't buy new fingers.

SnailsAttack

Hazard to Others

Posts: 166
Registered: 7-2-2022
Location: The bottom of Lake Ontario
Member Is Offline

posted on 4-3-2022 at 04:54

Quote: Originally posted by clearly_not_atara

Is it possible that one of them is Ca(OAc)2*xH2O and another is Ca(OAc)2*yH2O*zHOAc?

you mean maybe the calcium acetate is complexing with some leftover vinegar in solution? I think that could definitely be possible. if the beta morph is absorbing vinegar that might explain why it tends to forms last, since vinegar has a somewhat higher boiling point than water.

macckone

Dispenser of practical lab wisdom

Posts: 2168
Registered: 1-3-2013
Location: Over a mile high
Member Is Offline

Mood: Electrical

posted on 4-3-2022 at 12:08

Sodium acetate forms a diacetate, I would assume calcium would do the same if there is excess acetic acid.

AJKOER

Radically Dubious

Posts: 3026
Registered: 7-5-2011
Member Is Offline

Mood: No Mood

posted on 9-3-2022 at 10:50

Some comments per Atomistry at http://calcium.atomistry.com/calcium_acetate.html on crystallization products, to quote:

"Calcium Acetate, Ca(C2H3O2)2, crystallises from hot solutions in thin needles with 1 molecule, from cold solutions with 2 molecules of water of crystallisation. The transition point is at 84° C. At 20° C. 100 grm. of water dissolve 34.73 grm. of anhydrous calcium acetate, and at 100° C. 29.65 grm."

And also apparently, at times indeed an acid salt presence:

"With acetic acid and calcium nitrate a crystallised double compound is formed, and an acid salt, Ca(C2H3O2)2.C2H3O2, is obtained by treating solid calcium hydroxide with concentrated acetic acid."

Note: my observation is that Atomistry is a collection of dated (no copyright active) chemical journal accounts.

SWIM

National Hazard

Posts: 970
Registered: 3-9-2017
Member Is Offline

posted on 9-3-2022 at 11:25

YOU AGREE THAT THE INFORMATION IS PRESENT ON AN "AS IS" BASIS AND THAT atomistry.com IN NO WAY WARRANTS THE INFORMATION OR ANY OF ITS RESULTS AND IS IN NO WAY LIABLE FOR ANY USE YOU MAKE OF THE INFORMATION. IN NO EVENT SHALL atomistry.com BE LIABLE FOR ANY ACTUAL, DIRECT, INDIRECT, SPECIAL, CONSEQUENTIAL, OR INCIDENTAL DAMAGES, HOWEVER CAUSED, INCLUDING, WITHOUT LIMITATION, ANY DAMAGES ARISING OUT OF THE USE OF THE INFORMATION.

All information presented here is based on lectures given by author and also some information for this website was taken from the following sources:
--------------------------------------------------------------------------------------------------------------------
So it seems to actually be mostly from a series of lectures by one Sergey Ruzheinikov, born November 1973, a research associate from Sheffield U. At least he was until 2012 or so. Can't find later references to him on their site.

The atomistry site says he holds the copyright on these lectures.

[Edited on 9-3-2022 by SWIM]

Sciencemadness Discussion Board » Fundamentals » Chemistry in General » Dimorphism of Calcium Acetate