Question

You're provided with a bottle labled [CoCl2.6H2O] = 0.056 M in 4.60 M HCl. You heat a small volume of the solution in a hot water bath to 50 ∘C. If you determine that [CoCl42-] = 0.031 M at 50 ∘C at equilibrium, what must be the equilibrium concentration of [Cl-] at 50 ∘C?

Answer 1

Answer: Equilibrium concentration of $[Cl^-]$ at $50^0C$ is 4.538 M

Explanation:

Initial concentration of $CoCl_2$ = 0.056 M

Initial concentration of $Cl^-$ = 4.60 M

The given balanced equilibrium reaction is,

               $COCl_2+2Cl^-\rightleftharpoons [CoCl_4]^{2-}+6H_2O$

Initial conc.          0.056 M      4.60 M        0 M       0 M

At eqm. conc.     (0.056-x) M   (4.60-2x) M   (x) M    (6x) M

The expression for equilibrium constant for this reaction will be,

$K_c=\frac{[CoCl_4]^{2-}\times [H_2O]^6}{[CoCl_2]^2\times [Cl^-]^2}$

Given : equilibrium concentration of $[CoCl_4]^{2-}$ =x =  0.031 M

Concentration of $Cl^-$ = (4.60-2x) M  = $(4.60-2\times 0.031)$ =4.538 M  

Thus equilibrium concentration of $[Cl^-]$ at $50^0C$ is 4.538 M