Sciencemadness Discussion Board

Calcium Carbonate from Eggshells

javagamer - 25-9-2008 at 16:45

I'm a beginning chemist and I'm interested in the best way to extract calcium carbonate from eggshells. My current method is to clean out the egg gunk inside the eggs by hand, stick the eggshells in the toaster oven for a few minutes, then grind them up in a mortar and pestle. This method works fine except for removing the egg gunk by hand which is really a pain and probably not very efficient. I'm wonder if anyone here can suggest a better method to remove the egg gunk, maybe a solvent that doesn't dissolve the egg shells? Also, I know it is possible to by calcium carbonate over the counter, but at the moment I'm interested in what useful chemicals I can make for free from things most people have at home.
EDIT: Hints as to how I could figure this out myself are also appreciated.

Thanks in advance,

[Edited on 25-9-2008 by javagamer]

Magpie - 25-9-2008 at 17:33

Perhaps you could burn out the organic matter. My wife says that our self-cleaning oven literature claims it gets to 875F (468C). Probably would leave some carbon residue, however.

Or you could dissolve the CaCO3 in an acid (HCl) , filter saving the filtrate, then neutralize with baking soda. Then add further CO2 from a bubbler using vinegar and baking soda. This should precipitate out fairly pure CaCO3.

[Edited on 25-9-2008 by Magpie]

javagamer - 25-9-2008 at 17:42

I read somewhere that CaCO3 dissolves in vinegar, but I heard elsewhere that it reacts with vinegar and I'll be left with something else. Can someone clear this up for me?

bfesser - 25-9-2008 at 17:54

CaCO<sub>3</sub>(s) + 2 CH<sub>3</sub>COOH(aq.) -> Ca(CH<sub>3</sub>COO)<sub>2</sub>(aq.) + H<sub>2</sub>O(l) + CO<sub>2</sub>(g)

Calcium carbonate (base) reacts with the acetic acid in vinegar to form calcium acetate, water, and carbon dioxide. It's an acid-base reaction. Google/Wiki it.

[Edited on 9/25/08 by bfesser]

not_important - 25-9-2008 at 18:04

CaCO3 (solid) + 2 AcOH (liq) => Ca(OAc)2 (in solution) + CO2 (gas)

So vinegar dissolves CaCO3 by reactive with it. If an inorganic carbonate is insoluble in water then generally anything that dissolves it does so by reacting with it.

Heating the shells to 500-600 C in air will remove the organics, CaCO3 doesn't break down very fast below 800C, but there's other stuff than just CaCO3 in the shells. If you calcine the shells like that, then grind them, finally soaking them in colddistilled/deionised water for a hour so so and pour off the water - repeat several times - you'll get pretty pure CaCO3. Magnesium and phosphate are the major impurities, followed by sodium, potassium. Washing with water will remove the Na, K, and some Mg.

Attachment: Elemental and Ultrastructural Analysis of the Eggshell.pdf (634kB)
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bfesser - 26-9-2008 at 04:19

not_important, your equation is not_balanced. :P

javagamer - 27-9-2008 at 10:55

not_important: Doesn't calcium carbonate react with water? I heard a simple qualitative way to check whether you have calcium carbonate or calcium oxide is to add a little to water, the more bubbles you get the more calcium carbonate you have.

chemkid - 27-9-2008 at 15:33

That is not true. Calcium carbonate does not react with water. CaO reacts with water however there should be no effervescence (bubbling):

CaO + H2O --> Ca(OH)2

This is true of most alkali and alkali earth oxides.

Calcium carbonate will effervesce with acid. But calcium carbonate is not a base in some regards. This has to do with the different theories of acids and bases. (Bronsted, Lewis etc.)

All carbonates (or a lot of them) react like this:

H+ + CO3(2-) --> H2CO3

H2CO3 dissociates....

H2CO3 --> H20(aq) + CO2 (g)

The carbon dioxide is insoluble and comes off as a gas.


[Edited on 27-9-2008 by chemkid]

not_important - 28-9-2008 at 00:26

What chemkid said. Adding CaO to a not too large excess of water will boil the excess water. Calcium carbonate just sits there. Egg and sea shells are mostly calcium carbonate, as is coral and marble rock; if it was very reactive rain would make some building and statues interesting to be around, and imagine the ocean if CaCO3 reacted with plain water to give CO2.

kclo4 - 28-9-2008 at 01:29

I know it is possible to by calcium carbonate over the counter, but at the moment I'm interested in what useful chemicals I can make for free from things most people have at home.

Chalk is a pretty good source of Calcium Carbonate. Most people have this at home also. :D
just so you know

not_important - 28-9-2008 at 06:44

While many people may have 'chalk' at home, they may may not have calcium carbonate. Children's and blackboard chalk is often gypsum in part or whole, other 'chalks' can be talc or magnesium carbonate. Be sure to test you chalk before attempting to do a demonstration of the reaction of chalk and acid, it can be a bit embarrassing to add the acid and just have the mixture sit there inertly.

[Edited on 28-9-2008 by not_important]

kclo4 - 28-9-2008 at 11:24

Oh wow your right, didn't realize this, sorry about that!