A solution of Ca 2+ is added to a solution of SO4 2- and CO3 2- , what will precipitate first , CaCO3 or CaSO4?

1 Answer
anor277
Feb 8, 2018

Unknown in this scenario....

Explanation:

We do not know the concentration of calcium ion; nor do we know the concentrations of sulfate or carbonate ion. We do not know the solubility products of #CaSO_4# and #CaCO_3#... but these we can look up...

#CaSO_4(s) rightleftharpoonsCa^(2+) + SO_4^(2-)# #K_"sp"=4.93xx10^-5#

#CaCO_3(s) rightleftharpoonsCa^(2+) + CO_3^(2-)# #K_"sp"=3.3xx10^-9#

On these data, calcium carbonate is more insoluble than is calcium sulfate....and so the carbonate will precipitate first given equal concentrations of anions....

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