PCC Chemistry Competency Practice Exam

What is the net ionic equation for the precipitation reaction when BaCl2 and Na2SO4 are mixed in aqueous solution?

Ba2+ + 2Cl− → BaCl2(aq) BaSO4(s) precipitates directly from Ba2+ and SO4^2− Ba2+ + SO4^2− → BaSO4(s) Na+ + Cl− → NaCl

Correct Answer:

Ba2+ + SO4^2− → BaSO4(s)

Explanation:

When two aqueous solutions react to form a solid, the net ionic equation keeps only the ions that actually form the precipitate and removes the spectator ions that don’t participate in the solid formation. Here, BaCl2 provides Ba2+ and Cl−, while Na2SO4 provides Na+ and SO4^2−. The sulfate ion and the barium ion combine to make BaSO4, which is insoluble and precipitates. The sodium and chloride ions remain in solution and do not take part in the solid formation, so they’re removed in the net ionic form. Thus the net ionic equation is Ba2+ + SO4^2− → BaSO4(s).

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