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It doesn't melt in vinegar- rather, it dissolves in the acetic acid (H2C4O2)
Melting is a phase change- a physical process, not chemical.
The calcium carbonate (CaCO3) neutralizes the acetic acid (found in vinegar).
Reaction:
CaCO3(s) + 2 CH3COOH(aq) --> Ca(COOH)(aq) + CO2(g) + H2O (l)
Simply: a weak base reacting with a weak acid.
I've never tried this before but you could probably achieve the same results by placing a pearl in Coca-cola, or any common soda.
The phosphoric acid (relatively stronger than acetic acid) would dissolve it relatively quicker than acetic acid.
The carbonic acid could also facilitate the neutralization.
Reaction:
3 CaCO3 (s) + 2 H3PO4 (aq)<-> Ca3(PO4)2 + 3 H2O(aq) + 3 CO2(g)
/chemistry rant
OT:
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