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Name: Jeff
Status: other
Grade: other
Location: FL
Date: December 2007


Question:
How is Oxalic Acid H2C2O4 used to polish CaCO3. How can a strong acid produce a shine when the acid should be dissolving CaC03?



Replies:
Jeff,

Polishing, in this case, usually means dissolving a small top layer and leaving behind a smooth surface.

Greg (Roberto Gregorius)


Strong acids, at low concentration, polish reactive surfaces BY DISSOLVING the solid. With mechanical rubbing the acid preferentially dissolves the "high" spots thus leveling the peaks and valleys. Oxalic acid used to polish marble by also forming the complex salt Ca(C2O4). The key to using aggressive polishing agents like oxalic acid is LOW CONCENTRATION. You don't want the reaction to dissolve much of the solid surface, only the "peaks" that are exposed by rubbing.

Vince Calder



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