Question

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

Answer 1

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....