In: Chemistry
9. Calculate the solubility product of each of the following ions from the solubility given:
(a) AgBr, 5.7 x 10 - 7 mole/L
(b) PbF2 , 2.1 x 10 - 3 mole/L
(d) Ag 2CrO 4 , 4.3 x 10 - 2 g//L
Determine the Ksp of silver bromide, given that its molar solubility is 5.71 x 10¯7 moles per liter.
When AgBr dissolves, it dissociates like this:
AgBr (s) ⇌ Ag+ (aq) + Br¯ (aq)
The Ksp expression is:
Ksp = [Ag+] [Br¯]
There is a 1:1 molar ratio between the AgBr that dissolves and Ag+ that is in solution. In like manner, there is a 1:1 molar ratio between dissolved AgBr and Br¯ in solution. This means that, when 5.71 x 10¯7 mole per liter of AgBr dissolves, it produces 5.71 x 10¯7 mole per liter of Ag+ and 5.71 x 10¯7 mole per liter of Br¯ in solution.
Putting the values into the Ksp expression, we obtain:
Ksp = (5.71 x 10¯7) (5.71 x 10¯7) = 3.26 x 10¯13
Ksp = (5.71 x 10¯7) (5.71 x 10¯7) = 3.26 x 10¯13
(b) PbF2 , 2.1 x 10 - 3 mole/L
PbF2 (s) ⇌ Pb2+ (aq) + 2F¯ (aq)
The Ksp expression is:
Ksp = [ Pb2+] [F¯]2
= (2.1 x 10-3) (4.41 x 10¯3)2 =
Ksp = 4.0841 x 10-8
(d) Ag 2CrO 4 , 4.3 x 10 - 2 g//L
Ag 2CrO 4 (s) ⇌ 2Ag+ (aq) + CrO4¯ (aq)
Ksp = [ Ag+]2 [CrO4¯]
= [8.6 x 10-2]2 [4.3 x 10- 2]
Ksp= 3.18 x 10-5