MX is a solid that is slightly soluble in water. The equation for the equilibrium between dissolved substance and its ions as well as the reaction quotient expression Qs is given below.
MX(s)
M+(aq) + X–(aq)
For any solution
Qs = [M+][X–]
For a solution at equilibrium
Ks = [M+][X–]
Comparing the value of Qs for a solution containing the cation and anion of an sparingly soluble solid with the equilibrium constant Ks for the slightly soluble solid enables prediction of whether precipitate will form for a given solution or when two solutions are mixed.
The concentrations in the mixed solution can be calculated from given volumes and concentrations of solutions to be mixed.
MX(s)
M+(aq) + X–(aq)For any solution
Qs = [M+][X–]
For a solution at equilibrium
Ks = [M+][X–]
Comparing the value of Qs for a solution containing the cation and anion of an sparingly soluble solid with the equilibrium constant Ks for the slightly soluble solid enables prediction of whether precipitate will form for a given solution or when two solutions are mixed.
If M+ and X– are in the same solution, and their concentrations are given, these are used directly to calculate Qs.
If M+ and X– in different solutions which are then mixed. The concentration of these ions in the mixture must be used to calculate Qs. These concentrations can be calculated by
If M+ and X– in different solutions which are then mixed. The concentration of these ions in the mixture must be used to calculate Qs. These concentrations can be calculated by
The concentrations in the mixed solution can be calculated from given volumes and concentrations of solutions to be mixed.
- Calculate the amount in moles of solute present in the original solution (n = cV where c and V are the concentration and volume of the solution containing that ion before mixing).
- Multiply that amount in moles by the number of that type of ion present in the solute
- Dividing the result by the total volume in litres of the solution after mixing.