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Products and Equilibria of Reaction of Alum with Carbonates

If we were to add sodium carbonate and calcium carbonate to separate samples of Al2(SO4)3, what would the reaction/equilibrium equations look like?

What are the pKa values of Na2SO4 and CaSO4 ---- even though they are salts, would they continue to add at least in part to the acidity of the solution?

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Please see the attached file.

As for the acidity or basicity of sodium sulfate or calcium sulfate, you will find that sulfate is the conjugate base of an fairly strong acid (HSO4-). Its pKa is around 2. This means the pKb of sulfate is around 12 (pKw = pKa + pKb), which makes it a pretty weak base. Aside from that, any basic effects of the sulfate will be outweighed by the formation of CO2 by the reaction. This leads to a slight lowering of pH by causing the production of carbonic acid (a weak acid). It is my opinion that carbonic acid is a stronger acid than sulfate ion is ...

Solution Summary

The reaction products and equilibria of alum in wastewater are discussed in depth.The pKa values of Na2SO4 and CaSO4 are determined. The expert determines if they would continue to add at least in part to the acidity of the solution.

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