How do you write the Ksp equation?

1 Answer
Aug 16, 2017

Answer:

Well, for a start #K_"sp"=K_"solubility product"#, and we use an equilibrium expression.

Explanation:

For the sparingly soluble salt, #MX#, we write the equation that represents its dissolution:

#MX(s) stackrel(H_2O)rightleftharpoonsM^+ + X^-#

#K_"sp"=([M^+][X^-])/([MX(s)])#, but #MX(s)# as A SOLID cannot express a concentration, and thus the expression simplifies to...

#K_"sp"=[M^+][X^-]#

Usually standard conditions are specified, because a hot solution can generally hold more solute than a cold one.

For salts of the form #MX_2#, #K_"sp"=[M^(2+)][X^-]^2#. #K_"sp"#
have been measured for a host of insoluble, and semi-soluble ionic salts.

See here for more detail.