Please help me, i will give full points if you answered precisly and understanda

Question

Please help me, i will give full points if you answered precisly and understandably

Consider the endothermic reaction: in aqueous solution gives a red-colored solution, Br+ in aqueous solution is colorless, and CoBr42+ produces a blue color in aqueous solution. With equilibrium established in a system described by the equation above and with comparable concentrations of Co(H2O)62+ and CoBr42+, the solution color is purple. Write the equilibrium constant expression for the reaction shown above. If the solution temperature were lowered by 20 degree C, what solution color would you expect to see? Which as tge larger effect of the position of equilibrium: addition of 1 mL of liquid water or addition of 1 mL of 0.10 M AgNO3? What solution color do you expect to see after adding some ethanol, CH3CH2OH, to the solution?

Explanation / Answer

(a) (Co(H2O)6)2+(aq) + 4 Br-(aq) <=> (CoBr4)2-(aq) + 6 H2O(l)

Equilibrium constant K = [(CoBr4)2-]/[(Co(H2O)6)2+][Br-]^4


Note: Pure liquid term (H2O(l)) is left out of expression as it is effectively a constant value


(b) Since forward reaction is endothermic => it absorbs heat

(Co(H2O)6)2+(aq) + 4 Br-(aq) + heat <=> (CoBr4)2-(aq) + 6 H2O(l)


Lowering temperature => removing heat

=> equilibrium shifts to left according to Le Chatelier's principle

=> more (Co(H2O)6)2+ forms while (CoBr4)2- is consumed

=> color is red


(c) The answer is: addition of 0.10 M AgNO3

AgNO3 removes significant amounts of Br- from solution by precipitating insoluble AgBr:

AgNO3(aq) + Br-(aq) => AgBr(s) + NO3-(aq)


Removing Br- => equilibrium shifts to left according to Le Chatelier's principle


Adding H2O has little effect on equilibrium as [H2O] is effectively constant (water is the solvent) and adding another 1 mL is negligible.


(d) Ethanol does not react with any of the species in solution

=> it has no effect on the equilibrium position

=> color remains purple

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