Chemical Reactions: Precipitation and Solubility

What happens when the following compounds are mixed together: CaCl2, Na2S, Pb(NO3)2, (NH4)3PO4, Na2CO3, K2SO4, MgCl2, AgNO3?

The compounds that precipitate are CaCl2, Na2S, (NH4)3PO4, Na2CO3, and AgNO3. The compounds that remain soluble are Pb(NO3)2, K2SO4, and MgCl2.

Explanation:

Precipitation Reactions: When two soluble ionic compounds are mixed together, a precipitation reaction may occur if the possible cation/anion pairing results in the formation of an insoluble compound. Based on solubility guidelines, the compounds that precipitate are CaCl2, Na2S, (NH4)3PO4, Na2CO3, and AgNO3.
  • CaCl2 will form CaCO3
  • Na2S will form PbS
  • (NH4)3PO4 will form Pb3(PO4)2
  • Na2CO3 will form CaCO3
  • AgNO3 will form AgCl
Solubility: The compounds that remain soluble are Pb(NO3)2, K2SO4, and MgCl2.
  • Pb(NO3)2 will dissociate into Pb2+ and 2NO3-
  • K2SO4 will dissociate into 2K+ and SO42-
  • MgCl2 will dissociate into Mg2+ and 2Cl-
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