Calculating Ksp from Solubility Information

 

 

Given:  Solubility of Cu(OH)2 is 3.42 X 10-7 mol/L

Required:  Calculate the Ksp for Cu(OH)2

 

Solution:

 

1.  Write Equation:                                Cu(OH)2 (s) Cu2+ (aq) + 2 OH-(aq)

 

2.  Prepare chart           Initial Conc.          -                   0                          0

                                    Change                 -                 +3.42 X 10-7        +2(3.42 X 10-7)

                                    Equilibrium            -                   3.42 X 10-7          6.84 X 10-7

 

3.      Calculate Ksp

 

Ksp = [Cu2+][OH-]2

Ksp = [3.42 X 10-7][6.84 X 10-7]2

Ksp = 1.6 X 10-19

 

 

 

 

Your turn

 

Given:  solubility of Fe(OH)3 is 9.9 X 10-11 mol/L

Required:  calculate the Ksp of Fe(OH)3

 

1.  Write equation                                 Fe(OH) (s)

 

2.  Prepare chart           Initial Conc.

                                    Change

                                    Equilibrium

 

3.  Calculate Ksp

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Calculating Solubility from Ksp

 

Given:  Ksp of AgCl = 1.8 X 10-10

Required:  solubility of AgCl in pure water

 

Solution:

 

1.  Let the solubility of AgCl (s) be x mol/L

 

2.  Write equation                                             AgCl (s) Ag+ (aq) + Cl- (aq)

 

3.  Prepare chart                       Initial

                                                Change            

                                                Equilibrium

4.  Fill in chart

 

Ksp = [Ag+][Cl-]

1.8 X 10-10 =

 

x =

Therefore the solubility of AgCl (s) in pure water is ___________ mol/L

Therefore, ______ mol of AgCl dissolves in 1 L of solution, and the equilibrium concentration of the Ag+ ions = ________ mol/l and the equilibrium concentration of the Cl- ions is _______ mol/L.

 

Problems   p. 491 #1-3

 

For 2 (b)      mol  X  g  =  g  =  mg

                      L        mol   L      mL

 

I.e.         g  X  1000 mg  X        1 L     mg

            L             1 g           1000 mL     mL

 



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