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Solubility Rules

One of the factors driving a double-replacement reaction is the formation of a precipitate.  A precipitate is an insoluble solid compound formed during a chemical reaction in solution.  To predict whether a precipitate will form when you mix together two ionic reactants, you need to know whether any of the possible products are insoluble.  Considering the number of ionic compounds, it would be very difficult to memorize the solubilities of so many compounds. Fortunately we can group compounds into solubility categories. This is done with a set of eight rules called solubility rules.

         

           Rule Statement    Exceptions
1 All Group IA and ammonium compounds are soluble.         --
2 All Acetates and nitrates are soluble.         --
3 Most chlorides, bromides, and iodides are soluble. AgCl, Hg2Cl2, PbCl2, AgBr, HgBr2, Hg2Br2, PbBr2, AgI, HgI2,Hg2I2, PbI2
4 Most sulfates are soluble. CaSO4, SrSO4, BaSO4, Ag2SO4, Hg2SO4, PbSO4
5 Most carbonates are insoluble. Group IA carbonates, (NH4)2CO3
6 Most phosphates are insoluble. Group IA phosphates, (NH4)2PO4
7 Most sulfides are insoluble. Group IA sulfides, (NH4)2S
8 Most hydroxides are insoluble. Group IA hydroxides, Ca(OH)2, Sr(OH)2, Ba(OH)2






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