Chem2/5 Labs  
Ksp,  Solubility Product
Help


Know:

Prediction of effect on equilibrium of:
 
Concentration (adding or removing products or reactants)
Temperature (endothermic vs exothermic)

Be able to write the equilibrium constant expression for
a given solubility equilibrium reaction, based on its formula, 
and thus the number of ions produced.

(Remember, pure solids and liquids do not appear in 
the solubility product constant expression, 
only species in solution having concentrations.)


example: for As2S3(s) <==>  2As+3(aq)  +  3S-2(aq)

so the Ksp expression would be:  [As+3]squared x [S-2]cubed

A term for As2S3(s) does not appear, because it is a pure solid.

(sorry I cannot do subscripts and superscripts via HTML )

and if I were inserting molar values (s=molar solubility) for the ions:

[As+3] = 2s
[S-2] = 3s

Giving, for the relationship between Ksp and molar solubility:  

Ksp = [2s]squared x [3s]cubed = 108 x (s to the 5th power)

(NOTE, the most common mistake is to forget either 
the coefficient inside the brackets or to also use it as the exponent)