Cobalt ion exists as [Co(H_2O)]^2+ in aqueous solutions. The following equilibri

Question

Cobalt ion exists as [Co(H_2O)]^2+ in aqueous solutions. The following equilibrium reaction represents the two types of complexes of cobalt with two different colors. [C_0CI_4]^2 (aq. blue) + 6H_2O(1) [Co(H_2O)_4]^2+ (aq. pink) + Cl^-(aq) (a) What change in color do you expect when you add 10 drops of 12 M HCI to an aqueous solution of cobalt salt? Explain your answer in terms of LeChatlier principle. b) To the above mixture, if you add distilled water drop-wise what change you expect? Explain your answer in terms of LeChatlier principle. c) The above solution is divided equally into three test tubes a, B, C. Test tube "A" is placed in an ice bath kept at 0 degree C, test tube "B" is kept at room temperature (25 degree C) and test tube "C" is placed in a boiling hot water bath maintained at 100 degree C. The following are the colors of the solutions observed in each case. Solution "A" remained pink, solution "B" became dark pink and solution "C" turned blue. What do you conclude about the effect of temperature change on the position of equilibrium between cobalt complex ions (use the equation given above). Is the equilibrium reaction an exothermic or endothermic process? Explain.

Explanation / Answer

a) According to Le-Chtlier principle if the product concentration is increased, the equilibrium shifts to left side, reverse reaction rate increases. Thus addition of HCl , reverses the reaction and equilibrium goes to side of CoCl4-2 ion.

b) When water is added, the reactant concentration increases, Le- Chatlier principle says that the equilibrium goes in forward direction. Thus more products are formed.

c) the test tube A -at 0 C - has pink color

B at room temperature - dark pink

C at 100 c- blue

That is at high temperature the reverse reaction is favored and henc eblue color appered. That is the reverse reaction is endothermic reaction.

At low temperatures the pink color remained, that is forward reaction is favord. Thus the forward directioni is exothermic reaction.

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