Chapter 14 - Solubility Equilibria Flashcards
Define solubility.
Layman terms: ability to dissolve
Solubility of a salt is the number of moles/mass of solute/salt that can be dissolved in 1dm3 of a given solvent to form a saturated solution at a given temperature.
How is a dynamic equilibrium formed when a sparingly soluble salt is dissolved?
Upon addition of excess solute into a saturated solution, a dynamic equilibrium will be set up, where there is simultaneous dissolution of the excess undissolved solute and precipitation of the solution. These two processes take place at the same rate.
What is solubility product (Ksp)?
Ksp of a sparingly soluble salt is the product of the molar concentration of the constituent ions in a saturated solution, raised to appropriate powers (stoichiometric coefficient) at a given temperature. (Ksp changes with temperature only)
What is ionic product (IP)?
The IP of a sparingly soluble salt is the product of the molar concentrations of the constituent ions in the solution raised to appropriate powers (stoichiometric coefficient).
How can IP and Ksp be used to predict the occurrence of precipitation? (3)
- when IP < Ksp, there is less ions than saturation point, the forward reaction occurs (salt dissolves)
- when IP = Ksp, the solution is saturated
- when IP > Ksp, there is more ions than saturation point, backward reaction occurs (salt precipitates until IP=Ksp again)
What is selective precipitation?
It is the separation of ions in an aqueous solution by using a reagent that forms a precipitate with one or a few of the other ions but not all.
How can ions be separated from each other?
Add an ionic salt to a solution containing two cations. Ions can be separated based on the different solubilities of different salts: the less soluble salt precipitates first.
What are 3 factors affecting solubility?
1) common ion effect
2) formation of complex ion
3) pH
What is the common ion effect?
The solubility of a sparingly soluble salt decreases in the presence of a second solute that contains a common ion.
How does the common ion effect decrease solubility?
If a common ion was added to a salt solution, by LCP, the position of equilibrium will shift left to decrease concentration of newly added common ion. Thus less salt will dissolve, reducing its solubility.
How does the formation of complex ions increase solubility?
If an ion from the salt forms another complex ion with something else in a solution, the concentration of the ion decreases. By LCP, position of equilibrium shifts right to produce more of that ion, and thus more salt is dissolved, increasing its solubility.
How does changes of pH affect solubility?
When a bronsted acid/base is added to a solution containing a bronsted base/acid, the OH-/H+ ions will be neutralised and their concentration decreases. pH changes. By LCP, position of equilibrium shifts right, causing more salt to dissolve, thus increasing solubility.
