How To Dissolve Calcium Oxalate

Calcium oxalate is an ionic compound with the chemical formula CaC2O4 and a salt of oxalic acid. It's highly insoluble and dissolves poorly in water. One method for dissolving calcium oxalate in the lab is the application of a compound called ethylenediaminetetraacetic acid or EDTA. EDTA is highly effective at binding the calcium ions and thereby decreasing the concentration of calcium in solution, shifting the reaction equilibrium so that more calcium oxalate will dissolve. In the procedure outlined below, you'll first make calcium oxalate using common chemicals then dissolve it using EDTA.

Step 1

Put on the goggles and gloves. Oxalic acid and calcium oxalate are potentially toxic if ingested. Perform this experiment under the fume hood for safety.

Step 2

Measure out .032 ounces (.9 grams or approximately .01 moles) of oxalic acid into the beaker and add just under .338 fluid ounces (10 milliliters) of water. Swirl it gently in the beaker until the oxalic acid dissolves.

Step 3

Add .049 ounces (roughly 1.3 grams) of calcium chloride to the solution and swirl gently. As the reaction progresses, solid calcium oxalate will form and precipitate out of the solution. You now have calcium oxalate–the same substance from which kidney stones often form.

Step 4

Add about .01 ounces (.29 grams) of EDTA to the solution and swirl it gently in the beaker. Some of the calcium oxalate should begin to dissolve.