Eggshells in Vinegar - What Happened?
Most recent answer: 10/22/2007
- Anonymous (age 13)
St. Francis, Bakersfield, CA, USA
The reaction is: CaCO3+ 2H+ -> Ca+2 + H2O +CO2
(published on 10/22/2007)
Follow-Up #1: dissolving eggshells
Rialto Ca, USA
(published on 10/22/2007)
Follow-Up #2: egg shell in vinegar
- Theresa Estes
Walker, MO USA
I’m not sure your answer is as different as you think. Calcium acetate is somewhat water soluble, as you say. It goes into solution primarily as calcium ion Ca+2 and negatively charged acetate ions. So that’s what we showed. Since the acetate was there to begin with, it doesn’t appear in the formula showing what changed in the reaction. I don’t see how you get the reaction formula to balance without making an H2O, which would join the other water molecules already there. It’s true, however, that several different complexes of CO2 and water and its ions are in equilibrium in solution, so the CO2 produced isn’t all in the simple form.
(published on 10/22/2007)
Follow-Up #3: Effects of liquids on egg shells
- Gabby (age 13)
Nothing we could say would be as vivid or accurate as what you can observe yourself by doing the experiment. We do have something important to add, however. That oven cleaner can be quite nasty, so be sure to carefully follow all the handling guidelines- gloves, goggles, ventilation, etc. Some care is also good with the other cleaners.
(published on 02/22/2014)
Follow-Up #4: do eggshells completely dissolve?
- Arielle (age 18)
That is an excellent question to answer by doing the experiment. If I had to guess, some of the membrane that usually sticks on the inside of the shell wouldn't dissolve. But don't take my word for it.
(published on 02/24/2014)
Follow-Up #5: calcium acetate?
- Steven Lyod (age 19)
Tulsa, Oklahoma, united states of america
It's unclear what you think is inaccurate. So far as I can tell, we say what everybody says except that we describe part of the product as being Ca2+ rather than as calcium acetate. So I guess the issue is to what extent the calcium ion is free in solution and to what extent it's bound to the acetate ions. This website http://calcium.atomistry.com/calcium_acetate.html says on that issue, "The electrolytic dissociation of the salt in solution, calculated from the freezing-point lowering, is much greater than that indicated by the electrical conductivity". That sounds like many of the calcium ions may be loosely bound in hydrated complexes with acetate ions. (That's a little like the BeSO4 that I did some of my thesis on. Some of it goes into solution as free ions, some as a non-conducting hydrated neutral complex, and some as neutral molecules.) At this point you probably need a chemist if you want a more detailed description of what state the calcium ion is mostly in in vinegar.
The main point, however, is that other acids (e.g. HCl, citric, ...) also dissolve the eggshells. There's no special role played by the acetate. The acidity is the key. You can find a full discussion with lots of data here: http://en.wikipedia.org/wiki/Calcium_carbonate#Solubility_in_a_strong_or_weak_acid_solution. The solubility depends mostly on the pH and much less on the details of what other ions are around. So the common description of what's in solution as "calcium acetate" is misleading. It's clearer to think of it as the calcium ion.
(published on 04/28/2014)
Follow-Up #6: what dissolves eggshells?
- landon (age 13)
That sounds right to me. You can check by doing the experiment. Be careful with that toilet bowl cleaner, you'll need goggles and plastic gloves to work with it.
Let us know how it comes out.
(published on 12/08/2014)
Follow-Up #7: Why do we tell people to do the experiment?
- Rachel (age 55)
Blue Bell, PA
I can see why you might be frustrated to come to this page and not find "the answer." You're the first to mention a clogged garbage disposal or any other practical application—the previous questions were pretty clearly related to science fair-type projects. We usually encourage people to try those themselves first (after all, that's the point of a science fair) although we're happy to try to help explain their results. I'm jumping in for Mike here, so he can feel free to add anything he wants to say.
Consider this, as well: we're volunteers who do this for free to teach people about physics. There are a lot of questions we don't have time to respond to at all. More importantly, we may not know the answer to the question. I don't have the specific background knowledge to predict which household chemicals will or will not dissolve eggshells. Maybe a chemist would. If I had to know, I'd probably do an experiment.
Good luck with your garbage dispoal. Maybe I'll stop putting eggshells down mine...
Nothing to add to Rebecca's philosophy. On the eggshell issue, they're definitely not recommended for disposal, because they turn into a sort of heavy sand that sits in the pipes. They do make great garden compost. Vinegar should be good if it doesn't make problems for the pipes etc. It's environmentally benign. /Mike W.
(published on 03/23/2016)