Question

Calculate the Co²+ equilibrium concentration when 0.010 mole of Co(NH₃)₆₂ is added to a solution with 0.25 M NH₃. Assume the volume is 1.00 L.

a) 0.05 M
b) 0.10 M
c) 0.15 M
d) 0.20 M

Answer 1

The equilibrium concentration of Co2+ is approximately 0.000708 M.

Step-by-step explanation:

To calculate the Co2+ equilibrium concentration, we need to set up an ICE table for the reaction.

First, write the balanced equation:

[Co(NH₃)₆]²⁺ + H₂O ⇌ [Co(NH₃)₅(H₂O)]³⁺ + NH₄⁺

Next, set up the initial, change, and equilibrium concentrations. The initial concentration of Co(NH₃)₆²⁺ is 0.010 M since 0.010 mole was added to a 1.00 L solution.

The initial concentration of NH₃ is 0.25 M. Let's assume the equilibrium concentration of Co(NH₃)₆²⁺ is x.

The concentration of NH₃ will decrease by 6x while the concentration of NH₄⁺ will increase by x at equilibrium. Using the given equilibrium expression:

K = [Co(NH₃)₅(H₂O)]³⁺/[Co(NH₃)₆]²⁺[NH₄⁺]

Substituting the equilibrium concentrations, we get:

K = x/[0.010][0.25]

Simplifying, we find:

x = K[0.010][0.25]

Using the given value of K (0.283), we can calculate x:

x = 0.283[0.010][0.25] = 0.00070825 M

Therefore, the equilibrium concentration of Co2+ is approximately 0.000708 M.