The solubility of a compound represents the maximum amount of solute that can dissolve in a given solvent.
Soluble means that the compound is aqueous, breaks up into ions and can be classified as an electrolyte because it conducts electricity.
Insoluble means that the compound is a solid, liquid or gas, doesn’t break up into ions, can be classified as a non-electrolyte and does not conduct electricity.
How to Memorize the Solubility Rules
The Solubility Rules are a convenient set of guidelines to help us determine if an ionic compound will be soluble or insoluble. To determine the solubility of any ionic compound we can refer to the image below.
“The bank robber was GANA CASH his loot, but the COPS stopped him”
GANA CASH represents the ions that are normally soluble except for a few exceptions.
G represents the Group 1A ions from the Periodic Table: H+, Li+, Na+, K+, Rb+, Cs+, Fr+
A represents the acetate ion: C2H3O2–
N represents the nitrate ion: NO3–
A represents the ammonium ion: NH4+
C represents the chlorate and perchlorate ions: ClO3– and ClO4–
S represents the sulfate ion: SO42– (becomes a solid once it connects to Ca2+, Ba2+, Sr2+, Hg22+, Ag+ or Pb2+)
H represents the halogens, the elements from Group 7A: F –, Cl –, Br –, I – (become solids once they connect to Hg22+, Ag+ or Pb2+)
COPS represents the ions that are normally insoluble except for a few exceptions.
C represents the carbonate and chromate ions: CO32– and CrO42–
O represents the oxide and hydroxide ions: O2– and OH– (become soluble aqueous compounds once they connect to Ca2+, Ba2+, Sr2+)
P represents the phosphate ion: PO43–
S represents the sulfide ion: S2– (becomes a soluble aqueous compound once it connects to Ca2+, Ba2+, Sr2+)
The Solubility Rules go beyond just determining the physical state of a compound. Once you’ve mastered this concept you’ll apply it to writing balanced molecular equations, total ionic equations and net ionic equations.