Write a balanced net ionic equation to show why the solubility of Co(OH)2(s) (Ks

Question

Write a balanced net ionic equation to show why the solubility of Co(OH)2(s) (Ksp = 2.5E-16) increases in the presence of a strong acid and calculate the equilibrium constant for the reaction of this sparingly soluble salt with acid.

Write a balanced net ionic equation to show why the solubility of Co(OH)2(s) (Ksp = 2.5E-16) increases in the presence of a strong acid and calculate the equilibrium constant for the reaction of this sparingly soluble salt with acid.

Use the pull-down boxes to specify states such as (aq) or (s).

+

+

K = __________

         (aq) (s) (l) (g)

+

         (aq) (s) (l) (g)          (aq) (s) (l) (g)

+

         (aq) (s) (l) (g)

Explanation / Answer

Solubility of salts

Chemical equations,

Co(OH)2(s) <==> Co2+(aq) + 2OH-(aq)     Ksp

2H+(aq) + 2OH-(aq) <==> 2H2O(l)             1/Kw

adding,

Co(OH)2(s) + 2H+(aq) <==> Co2+(aq) + 2H2O(l)   K = Ksp/Kw

Ksp = 2.5 x 10^-16

Kw = 1 x 10^-14

So,

equilibrium constant K = 2.5 x 10^-16/1 x 10^-14 = 0.025

So as can be seen, adding strong acid (H+), the soluble OH- ions in solution reacts with H+ added and forms H2O(l). This reduces the concentration of OH- on the right handside of the Ksp equation. Therefore, more of Co(OH)2 dissolves in solution. This can also be seen from K equation, H+ reacts to form more Co2+(aq) in solution. Thus solubility of sparingly soluble salt Co(OH)2(s) increases upon addition of strogn acid.

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