Chapter 17 - Solubility

Question 1

When does percipitation occur?

Answer 1

When Q is greater than Ksp becuase the solution is beyond saturation

Question 2

True or false? The system is at equilibrium when Q = Ksp

Answer 2

True

Question 3

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]).
𝑲𝒔𝒑 𝒐𝒇 𝑨𝒈𝑪𝑵 = 𝟏. 𝟐 × 𝟏𝟎−𝟏𝟔
𝑲𝒂 𝒐𝒇 𝑯𝑪𝑵 = 𝟔. 𝟐 × 𝟏𝟎−𝟏

Answer 3

1. Write out both the equilibrium constant expression and the dissolution constant expression.
2. At equilibrium Q = Ksp so you find the CN- value which makes this so

Q = [Ag+][CN-]
This CN- value is at equilibrium

3. Then you sub in this value into the Ka expression to find the H3O+ concentration
4. 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

Question 4

Outline the important insoluable salt

Answer 4

AgCl = Ag+ + Cl-

Question 5

Define molar solubility

Answer 5

of moles that will dissolve in 1L of solvent

Question 6

When is Ksp used?

Answer 6

only for poorly soluable salts

Question 7

What is teh common ion effect in relation to solubility

Answer 7

The addition of soluble salt that shares a common ion with insoluble salt reduces solubility of insoluble salt

Question 8

when does pH affect the solubility of salts

Answer 8

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

Question 9

When will lower Ksp percipitae?

Answer 9

At lower concentration of precipitating ion

Question 10

How to solve selective precipitation questions

Answer 10

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

Question 11

Find molar solubility of AgCl in 0.1M NH3(aq)

Answer 11

1. Create expression for Ka and for Ksp
2. Add both equations and multiply K’s to get overall K
3. Solve the ice table for S

Question 12

If you have 0.1 + S, when do yuo neglect the 0.1 and the S

Answer 12

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