When does percipitation occur?
When Q is greater than Ksp becuase the solution is beyond saturation
True or false? The system is at equilibrium when Q = Ksp
True
To an aqueous solution originally containing 1.0 x 10-4 mol/L Ag+ was
added enough of the weak acid HCN to reach an equilibrium concentration of [HCN] = 3.0 x 10-4
mol/L. What must be the pH of the solution in order to observe a precipitate of AgCN?
(Hint: Assume any change in pH will not change the value of [HCN]).
π²ππ ππ π¨ππͺπ΅ = π. π Γ ππβππ
π²π ππ π―πͺπ΅ = π. π Γ ππβπ
- Write out both the equilibrium constant expression and the dissolution constant expression.
- At equilibrium Q = Ksp so you find the CN- value which makes this so
Q = [Ag+][CN-]
This CN- value is at equilibrium
- Then you sub in this value into the Ka expression to find the H3O+ concentration
- Following this you take the log to find the pH, and in order for precipitation to occur, the pH must be higher than this value
Outline the important insoluable salt
AgCl = Ag+ + Cl-
Define molar solubility
of moles that will dissolve in 1L of solvent
When is Ksp used?
only for poorly soluable salts
What is teh common ion effect in relation to solubility
The addition of soluble salt that shares a common ion with insoluble salt reduces solubility of insoluble salt
when does pH affect the solubility of salts
when anion is the conjugate base of a weak acid, because in acidic conditions the conjugate base reacts with H+ to form weak acid, shiftning equilibrium away and increases solubility
When will lower Ksp percipitae?
At lower concentration of precipitating ion
How to solve selective precipitation questions
Identify reagent and write out dissociation equations along with K for each
Precipitation occurs when Q is greater than KSP so setup that inequality and solve for what the concentraction of OH or H has to be
Find molar solubility of AgCl in 0.1M NH3(aq)
- Create expression for Ka and for Ksp
- Add both equations and multiply K’s to get overall K
- Solve the ice table for S
If you have 0.1 + S, when do yuo neglect the 0.1 and the S
You neglect the solubility if it is very small compared to the inita lconcentration of the ion
You neglect inital concentration if it is very small compared to the solubility
