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Calcium carbonate gel?

Calcium carbonate gel? - Chemistry Forum

Calcium carbonate gel? - Chemistry Forum. Discuss chemical reactions, chemistry.


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  #1  
Old 11-05-2003, 06:01 AM
Repeating Decimal
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Default Calcium carbonate gel?



Upon mixing solutions of calcium chloride and sodium carbonate, I got a
gelatanous precipitate of calcium carbonate. Where can I find information on
the structure of such a gel? Google does not work for me although I got lots
of information on how to treat HF exposure.

Bill

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  #2  
Old 11-06-2003, 12:51 AM
Steve Turner
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Default Calcium carbonate gel?

Repeating Decimal <[Only registered users see links. ]> wrote:


HF exposure????

This is not an answer to your question, but I wonder about the
stability of this gel you're getting. When I was just starting out in
chemistry many moons ago I made CaCO3 via double decomposition from
CaCl2 and Na2CO3. I don't remember any gel. The precipitate was
filterable using typical home lab supplies (i.e., paper towel filter
in a funnel).

Does your gel collapse to a more typical precipitate with vigorous
stirring? Is its formation dependent on stoichiometry or order of
mixing or --??

Steve Turner

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  #3  
Old 11-06-2003, 01:33 AM
Gregg
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Default Calcium carbonate gel?


"Repeating Decimal" <[Only registered users see links. ]> wrote in message
news:[Only registered users see links. ]...
on
lots
What is the concentration of your initial solution?
Could it be flocculated CaCO3? - If the ionic strength of your solution is
high after precipitating and solids are high enough- you could end up with a
thick flocculated paste.
Try blowing a little CO2 into the slurry and see if the viscosity lowers. I
don't know the IEP point of CaCO3 off hand, but should be high. The CO2
should increase the particle charge and precipitate any remaining Ca++.
Gregg


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  #4  
Old 11-06-2003, 01:58 AM
Repeating Decimal
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Default Calcium carbonate gel?

in article [Only registered users see links. ], Steve Turner at
[Only registered users see links. ] wrote on 11/5/03 4:51 PM:


HF exposure is a bit of a red herring. Most of the Google hits were on that.

I did not do extensive experiments. When I mixed monohydrated sodium
carbonate (obtained as a photochemical several decades ago) with calcium
chloride and water, I got a gelatinous mass that reminded me of some
experiments I did very long ago with waterglass, sodium silicate. There was
a big drop in pH below that of the alkaline soda or the almost neutral
calcium chloride solution.

Bill

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  #5  
Old 11-06-2003, 03:00 AM
Gregg
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Default Calcium carbonate gel?


"Repeating Decimal" <[Only registered users see links. ]> wrote in message
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that.
was
I do some work with precipatating alkali-earth carbonates and I havn't run
across a clear gel.
I've read about some amorphorpous gels being formed in the presence of
chelating agents and under reflux conditions.-
I can dig up the references if you would like them.
I am very interested in what may have happened in your experiments if you
feel inclined to share details.

Gregg


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  #6  
Old 11-06-2003, 03:34 AM
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in article rxhqb.2474$[Only registered users see links. ].adelphia.net, Gregg at
[Only registered users see links. ] wrote on 11/5/03 5:33 PM:

This was a variation of a crude experiment suggested by a TV program
designed for elementary school. I did not keep good records.

The original experiment called for mixing NaHCO3 with CaCl2 and water.
There was lots of fizz. As a control, I substituted Na2CO3 for NaHCO3. That
is when I got the gel.

Bill

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  #7  
Old 11-06-2003, 03:40 AM
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Default Calcium carbonate gel?

in article 9Piqb.2495$[Only registered users see links. ].adelphia.net, Gregg at
[Only registered users see links. ] wrote on 11/5/03 7:00 PM:


I am going to demonstrate these reactions this weekend to some people that
gather every month. They, like me, are not primarily chemists. This time, I
will measure out the ingredients, at least by spoonfuls, and measure the
added water. I will record pH at the various steps. Then we can be more
definite.

Bill

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  #8  
Old 11-06-2003, 04:46 AM
hanson
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Re: Calcium carbonate gel?"Repeating Decimal" <[Only registered users see links. ]>
wrote in messages
news:[Only registered users see links. ]...

It appears me to that when you have at low temp (RT) &
a high conc. of the reactants, mixed fast and well, in the
stochiometric right proportions per Na2CO3+CaCl2 you will
get many nucleations in a small volume (due to exceeding
the solubility prod). This then simply means that you obtain
a slurry of CaCO3 whose xx are so many and so small that
the product appears as a translucent gelatinous product.

This "gelatin" will quickly turn opaque and then milky white
upon standing or heating due to the agglomeration of the
CaCO3 xx into larger crystals. You'll end up with a fine white
sediment of CaCO3 with a clear supernatant liquid of NaCl.

In the initial stages of the formation there may also be a
transition from originally formed CaCO3 ppt as aragonite xx
in to the calcite form (or vice versa/forgot). Aragonite
(orthorhombic) is a polymorph of calcite, (trigonal), both
CaCO3, and there is even 3rd rare form Vaterite (hexagonal).
Calcite is the most stable and hence the most abundant
form of CaCO3.

It is interesting to note that marine creatures, coral and
bivavles produce aragonite structure. If a technology can
be developed that generates fast and easy, dense CaCO3
mono- or coherent poly- crystalline structures, instead
of the usual amorphous ppts, in a simple fashion out of
aqueous solutions, you'll be a billionaire real fast.
The process will go thru the stage of the gelling you have
observed.
hanson


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  #9  
Old 11-06-2003, 06:48 AM
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Default Calcium carbonate gel?

in article Tmkqb.2960$[Only registered users see links. ].pas.earthlink.n et, hanson at
[Only registered users see links. ] wrote on 11/5/03 8:46 PM:


I do believe that you have hit the nail on the head. There was high
concentration. I do not know what the notation "xx" means.
Is this dense structure pearl?

Bill

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  #10  
Old 11-06-2003, 04:29 PM
hanson
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"Repeating Decimal" <[Only registered users see links. ]> wrote in message
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Bill, you are a good observer. But mind you hi-conc is only
one of many (perhaps the most influential) parameters. The
field of xx initiation is extremely complex under closer scrutiny.


"xx" is an old abbreviation for
"crystal(s), crystallization or crystalline"

Yes, Bill, dense structure pearl (pearlmutter) material has
applications for mass producing fake pearls and such jewelry
without the oyster in the sea, for uses in restoring historic and
archeo treasures, demand for it in the billion$ industry of sealing
anodized aluminum, the use for coating the insides of pipes
for drinking water, imagine such a solvent free mother of pearl
liquid/cream with which you could coat a dull looking drywall, etc, etc.
The potential of applications for this form of CaCO3 are immense.
Take care, dude,
hanson

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