1. Solubility Curves

2. Solubility curves
Solubility curves can be used to show the how much of a solid will dissolve at a given temperature
By convention solubility curves are graphed as solubility (g/100g of H2O)
So how many grams of a solid can be dissolved in 100g of water
100g of water =100 mL of water

3. Temperature (oC) 25 50 75
100
Solubility(g/100 g H2O)
150
Supersaturated
solution
Unsaturated
Saturated

4. Practice problems
If you put 40g of potassium chloride in 100g of water what is the lowest temperature that could be used while still dissolving all of the potassium chloride.

5. Practice problems
How much calcium chloride could you dissolve in 150g of water at 20⁰C?

6. Practice problems
If 50g of potassium dichromate is placed in 100g of water at 50⁰C will the solution be unsaturated, saturated or supersaturated?

7. Practice problems
Which of the following is the most soluble at 60⁰C: Potassium chloride, potassium chlorate, or sodium chloride?

8. Practice problems
At 40⁰C if 80g of potassium chloride is placed in 140g of water what ions and molecules will be present?

9. Common ion effect
What happens if we add a solid to a solution which contains a common ion or molecule?
Ex. A solution containing M F2 has solid calcium fluoride added. What is the molar solubility of calcium fluoride when placed into this solution?
Ca2+ F2 I C E

10. Ex. 2
A solution of 2.0 M beryllium hydroxide is prepared and completely dissociates into its ions. Solid silver hydroxide is added to the solution, what is the molar solubility of the silver hydroxide in this solution?
Ag+
OH- I C E

11. Common Ion Effect
When a solution is made with two compounds that share a common ion the molar solubility (s) is lowered.
For example if sodium hydroxide (which completely dissociates) and silver hydroxide are placed in solution they will dissociate into their respective ions
NaOH(s)  Na+(aq)+ OH-(aq)
AgOH(s)  Ag+(aq) + OH-(aq)
Because AgOH is not very soluble there may be some solid AgOH dependant upon how much is added.
Common Ion

12. Example problem 3:
Silver hydroxide is added to a solution of mol/L sodium hydroxide. Find the molar solubility of silver hydroxide in this solution.
Step 1: State the separate chemical equations for the dissociation of sodium hydroxide and silver hydroxide
NaOH(s)  Na+(aq)+ OH-(aq)
AgOH(s)  Ag+(aq) + OH-(aq)

13. Example problem:
Step 2: Set up an Ice table for the compound you are finding molar solubility for
Step 3: Determine the concentration of the common ion. Remember to look at the coefficients of the original solution. This is your Initial concentration on the ice table.
Ag+
OH- I C E

14. Example problem:
Step 4: Fill in the rest of the ICE table, remember coefficients.
Step 5: state the Ksp equation: Ksp=[Ag+][OH-]
DO NOT forget to include any coefficients as exponents.
Ag+
OH- I
0.200 M C E

15. Example problem:
Step 6: substitute concentrations from equilibrium (E) into the Ksp equation, state what Ksp for this compound is.
Ksp = (s) (0.200+s) Ksp=
Step 7: Assume “s” is small because Ksp is small, s still equals , just like the “x” is small approximation.
Ag+
OH- I
0.200 M C +s E S
0.200+s

16. Example problem:
Step 8: solve for “s”, the molar solubility. Remember “s” is in mol/L and represents how many moles of silver hydroxide can be dissolved in 1L of this solution.
Ksp= s(0.200)
Ksp/0.200 = s s=
Ag+
OH- I
0.200 M C +s E S
0.200+s