Carboxylic acids and related compounds
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Which is more soluble, calcium oxalate or silver oxalate. I know that the value for calcium oxalate is 2.3 x 10–9 (mol per 100 g?), but I do not seem to be able to find a value for silver oxalate.
Igloo writes
Presumably you obtained your value for calcium oxalate (calcium ethanedioate) from the Nuffield Book of Data.
I have access to what is known as the CRC Handbook of Chemistry and Physics (at my local library). This is a 3-4 inch thick book listing most physical and chemical constants, and if a value isn’t in this document, it is probably not easily found in any other! If you seek data in the future try the reference department of the library at your local town or city.
Well, according to the data in this book, the solubilities are as follows:
CaC2O4 0.00067 g per 100 cm3 of water at 13 °C
Ag2C2O4 0.00339 g per 100 cm3 of water at 18 °C
What a pity that the data isn’t available for the same temperature, let alone the standard temperature of 298 K ! As it happens I doubt whether the actual solubilities will vary too greatly over a range of 5 °C, but I wouldn’t be sure.
Anyway, if you need your data in mol per 100 cm3 you will need to divide these values by the molar mass of each substance. Since Mr[Ag2C2O4] is much greater than Mr[CaC2O4], it wouldn’t surprise me that in terms of molar quantities, calcium oxalate came out with a higher solubility, whereas in mass units, as you can see, the solubility of calcium oxalate is about 5 times lower.
In summary, there isn’t a great deal of difference between the two. Neither is very soluble at all. If you’re carrying out an experiment in which you are relying on a certain mass of precipitate to be formed, then the mass data I have given you is probably more relevant.
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updated: 27 August 2003
