Solubility and Spectator Ions
Precipitates are electrically uncharged. In this experiment all of the precipitates result from the exchange of positive and negative ions between reacting solutions of two ionic compounds. Thus, in this example the precipitate must be either silver chloride, AgCl or sodium nitrate, NaNO3. Sodium nitrate dissolves readily in water and is therefore soluble. Thus we can conclude that silver chloride is the insoluble precipitate. We can represent the formation of this precipitate by a net ionic equation:
Ag+ +NO3 ̄ +Na++Cl ̄→AgCl+NO3 ̄+Na+ Net: Ag+ (aq)+Cl ̄ (aq)→AgCl(s)
Ions present in the solution but not involved in forming the precipitate are called spectator ions; in our example these would be Na+ and NO3-. Spectator ions are not recorded in net ionic equations. To help identify (or predict) which compounds are soluble or insoluble most chemistry texts contain solubility rules and tables.
Basic Solubility Rules:
A. Nitrates: All nitrate salts are soluble.
B. Alkali metals: The salts of lithium, sodium, potassium, rubidium, and cesium are generally very soluble.
C. Ammonium salts: Almost all ammonium salts are soluble.
D. Sulfates: The sulfates of most common elements are soluble, except those of calcium, strontium, barium, and lead (II) ions.
© 2010 Hands On Labs, Inc. LabPaq CK-1 103
E. Hydroxides: Most of the hydroxides are insoluble, except those of the alkali metals and barium; calcium hydroxide is moderately soluble.
F. Halides: The chloride, bromide, and iodide salts are generally soluble, except those of silver, lead (II), and mercury (I) ions.
G. Sulfides: Most sulfides are insoluble, except from alkali metals and ammonium ion.
H. Acetates: All acetates are soluble, except silver acetate, which is slightly soluble.
I. Silver salts: All silver salts are insoluble, except silver nitrate, silver nitrite, and silver perchlorate. Silver acetate and silver sulfate are slightly soluble.
J. Carbonates: All carbonates are insoluble, except those of
Ag+ +NO3 ̄ +Na++Cl ̄→AgCl+NO3 ̄+Na+ Net: Ag+ (aq)+Cl ̄ (aq)→AgCl(s)
Ions present in the solution but not involved in forming the precipitate are called spectator ions; in our example these would be Na+ and NO3-. Spectator ions are not recorded in net ionic equations. To help identify (or predict) which compounds are soluble or insoluble most chemistry texts contain solubility rules and tables.
Basic Solubility Rules:
A. Nitrates: All nitrate salts are soluble.
B. Alkali metals: The salts of lithium, sodium, potassium, rubidium, and cesium are generally very soluble.
C. Ammonium salts: Almost all ammonium salts are soluble.
D. Sulfates: The sulfates of most common elements are soluble, except those of calcium, strontium, barium, and lead (II) ions.
© 2010 Hands On Labs, Inc. LabPaq CK-1 103
E. Hydroxides: Most of the hydroxides are insoluble, except those of the alkali metals and barium; calcium hydroxide is moderately soluble.
F. Halides: The chloride, bromide, and iodide salts are generally soluble, except those of silver, lead (II), and mercury (I) ions.
G. Sulfides: Most sulfides are insoluble, except from alkali metals and ammonium ion.
H. Acetates: All acetates are soluble, except silver acetate, which is slightly soluble.
I. Silver salts: All silver salts are insoluble, except silver nitrate, silver nitrite, and silver perchlorate. Silver acetate and silver sulfate are slightly soluble.
J. Carbonates: All carbonates are insoluble, except those of