(EXCEPTIONS: Cations Ag + , Pb 2+ , Hg 2 2+ ). d) Most compounds containing SO 4 2- (sulfate ion) are soluble . (EXCEPTIONS: Cations Ag + , Pb 2+ , Hg 2 2+ , Ca 2+ , Sr 2+ , Ba 2+ ). e) Most compounds containing OH - (hydroxide ion) are insoluble . (EXCEPTIONS: Cations from group 1A, Ca 2+ , Sr 2+ , Ba 2+ ). f) Most other compounds are insoluble . (EXCEPTIONS: Compounds covered by rules a-e).
Use of Solubility Rules Which of the following ionic compounds is soluble in water? KClO 4 (NH 4 ) 2 SO 4 CuCl 2 PbI 2 NiSO 4 Mg(OH) 2 Zn(IO 3 ) 2
Use of Solubility Rules KClO 4 soluble Rules a and b (NH 4 ) 2 SO 4 soluble Rule a CuCl 2 soluble Rule c PbI 2 insoluble Rule c NiSO 4 soluble Rule d Mg(OH) 2 insoluble Rule e Zn(IO 3 ) 2 insoluble Rule f
Determining Whether a Precipitation Reaction Will Occur When solutions of two soluble substances mix we will not always form a precipitate. We may use the solubility rules to decide if a precipitate will form. 1) Write the ions formed from the starting compounds. 2) Look at all possible combinations of cations and anions. a) If there is a combination of ions that forms an insoluble compound, a precipitate will form and a precipitation reaction occurs. b) If there is not a combination of ions that forms an insoluble compound, then there will be no precipitation reaction.
Examples: For each of the following mixtures of two solutions will a precipitate form? Note that all of the solutes are themselves soluble. Solution A solution B precipitate(?) 1) NaCl(aq) AgNO 3 (aq) 2) NaCl(aq) CuBr 2 (aq)
Solution A solution B precipitate(?) 1) NaCl(aq) AgNO 3 (aq) yes, AgCl(s) Na + Cl - Ag + NO 3 - NaCl(aq) + AgNO 3 (aq) NaNO 3 (aq) + AgCl(s) 2) NaCl(aq) CuBr 2 (aq) no Na + Cl - Cu 2+ Br - No reaction.
Net Ionic Equations To this point we have written chemical equations in terms of neutral species (molecules, or formula units). However, in aqueous solution it is often more appropriate to write equations in terms of ions. There are three ways we normally write chemical equations: 1) Molecular equation . All reactants and products are written in terms of their chemical formula. 2) Total ionic equation . Strong electrolytes (strong acids, strong soluble bases, and soluble ionic compounds) are written as ions. 3) Net ionic equation . The total ionic equation after removing spectator ions . A spectator ion is an ion that appears on both the reactant and product side of the equation, and which does not participate directly in the chemical reaction.
Net Ionic Equation (Example) We may show the various ways of writing chemical reactions as follows: Molecular AgNO 3 (aq) + NaCl(aq) NaNO 3 (aq) + AgCl(s) Total Ionic Ag + (aq) + NO 3 - (aq) + Na + (aq) + Cl - (aq) Na + (aq) + NO 3 - (aq) + AgCl(s) Net Ionic Ag + (aq) + Cl - (aq) AgCl(s)
Finding the Total and New Ionic Equations We find the total and net ionic equations as follows. 1) Begin with a balanced molecular equation.