sea shells

[budullewraagh]

how much CaCO3 is in sea shells?

 

when dissolved they should become basic, no?

[Mr_Mediocre]

There is quite alot of CaCO3 in seashells! This compound is only slightly soluble in water, however, and is stabilized in seashells by the matrix into which it is incoporated, so is even less soluble. If you would like to do a little test, you could sit a seashell in vinegar overnight, testing the pH beforehand, and afterwards. You should see a rise to around pH 7 if you use enough seashell.

 

If you have access to a decent balance, and an AAS (Atomic Absorption Spectrometer) with a calcium lamp, you could dissolve the seashell (after weighing it) in excess HCl, dilute it suitably (may require a few dilutions to get it right), then (after doing a standard curve with known Ca2+ standards) determine EXACTLY what percentage Ca2+ (by mass) was in your shell.

 

There is a titration you can do if you dont have an AAS...

 

http://www.ce.udel.edu/courses/CIEG%20437/lab02-2003.doc

 

[budullewraagh]

yeah, i decided to make calcium salts the other day. i started with calcium acetate (simple, no?).

i crushed my shells into a fine powder, then added some to a beaker with some ethanoic acid. not all the shells dissolved and it took quite awhile to finish the reaction. when i went to distill it, i turned on my burner and almost instantly the solution released a vapor that looked like water vapor. do you know why this was produced? i checked my merck index and it states that calcium acetate doesn't become anhydrous until higher temperatures

[Mr_Mediocre]

There vapour was probably trapped gas becoming liberated first, then water vapour closer to 80 C. From your solution should have been able to isolate Ca acetate monohydrate. What strength acetic acid did you initally use?

[budullewraagh]

heh, 3%

[Mr_Mediocre]

If you use a good excess of vinegar then boil it all down you might get calcium acetate monohydrate precipitating upon cooling. You'll have to muck around with it a little I think, but that's half the fun

[Toothpick93]

The vapors that came off the calcium acetate when heated was most likely acetone