#K_(sp)#, the #"sp"# stands for #"solubility product"#, is another equilibrium constant, and measures the solubility of an insoluble or sparingly soluble salt. As with any equilibrium, standard conditions are assumed, i.e. #298*K#, and #1*atm# pressure.
The larger the #K_(sp)# constant, the more soluble is the salt. Silver halides are the classic insoluble salts, and #K_(sp)# measures the extent of the following reaction:
#Ag^(+) + X^(-) rarr AgX(s) darr#
#K_(sp)# #=# #[Ag^+][X^-]# (of course #[AgX(s)]# does not appear in this equilibrium expression in that we cannot speak of the concentration of a solid.
#K_(sp), AgX:# #X=Cl, 1.8xx10^-10;#
#X=Br, 5.0xx10^(-13);#
#X=I, 8.5xx10^(-17)#
From the list, it is clear that #AgI# is the least soluble species.
#K_(sp)# are extensively tabulated, especially for salts of precious metals. How do you think #K_(sp)# values would evolve at higher temperatures? Say. #323*K#?
