Sulfate Ion, SO42-
Sulfate ion is a very weak base, while HSO4- is a fairly strong acid, with Ka = 0.01. On the other hand, H2SO4 is a very strong acid. Because it is such a weak base, sulfate ion undergoes negligible hydrolysis in aqueous solution.
Most sulfates, including those of Na+, K+, and NH4+, are soluble in water. Exceptions that are insoluble are white lead(II) sulfate and white barium sulfate:
Formation of white BaSO4 upon addition of Ba2+ to a solution of SO42-, even if it is acidic, is a reliable test for sulfate. Other insoluble sulfates are those of calcium, strontium, and mercury(I).
Sulfate is a very weak oxidizing agent. Since sulfur is in its maximum oxidation number in sulfate ion, this ion cannot act as a reducing agent.
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