MadSci Network: Chemistry

Re: Solubility of calcium carbonate

Date: Wed May 12 20:22:17 1999
Posted By: Charlie Crutchfield, , Retired, Retired
Area of science: Chemistry
ID: 926182697.Ch

Dear Student, My calculations agree with yours. Also, this reaction is used in industry to prepare "synthetic chalk", so there should be no hidden gremlins. At this distance, I cannot question your technique, etc. I suggest that you examine your reagents, look carefully at the labels. The Sodium Carbonate may be the mono-hydrate[sometimes a manufacturer will neglect to tell you such "minor" details] In which case 5 grams of the MONO-hydrate would react with 5 grams of Calcium Chloride [anhyd.] to form about 3.89 grams Calcium Carbonate. Or, maybe a little less, since the "excess" ca;cium chloride might cause the solution to be a little acidic, which would prevent complete precipitation of the Calcium Carbonate. Alternately, the Calcium Chloride actually may be the di-hydrate. "Flake" and "USP" Calcium Chloride is usually the di-hydrate, but it may not be so labelled. If this is the case, using 5 grams of the DIHYDRATE would yield 3.43 grams of Calcium Carbonate. This latter is fairly close to your result of 3.328 grams. Also, regardless of the label, both of these reagents, especially the Calcium Chloride, are hydroscopic, which could cause the results to be even less than my calculations of 3.89 or 3.43 grams. I have tripped over this "rock" myself more than oncein the past, which is what reminded me of this possibility. Please let me know if this is the correct answer to your problem, I am very curious. Charlie Crutchfield

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