A student doing the experiment in this module extended the study of the [CoCI_4]

Question

A student doing the experiment in this module extended the study of the [CoCI_4]^2 ion/[Co(H_2O)_4]^2+, ion equilibrium. In one test tube, the student added silver nitrate (AgNO_3) to a blue equilibrium mixture prepared from CoCl_2. The reaction mixture became pink and cloudy, and a white precipitate settled out leaving a clear, pink solution. The student identified the precipitate as silver chloride, AgCl. Briefly explain how these observations are consistent with lessthanorequalto Chatelier's principle. In a second test, the student placed a test tube containing a pink equilibrium mixture in a hot-water bath. The solution turned blue. When the student removed the test tube from the hot-water bath and placed it in an ice-water bath, the solution turned pink. Is the forward reaction in the [CoCl_4]^2- ion/[Co(H_2O)_4]^2+ ion equilibrium exothermic or endothermic? Briefly explain how the student's observations support your answer to (2). Write the net ionic elation for this equilibrium, including heat.

Explanation / Answer

Q1

lechatelier principle states that the equilibirum will be always achieved, so for every action, there will be a reaction to counterbalance the equilibrium.

clearly, from here, CoCl2 and AgCl have common ions, therefore addition of Cl- ions will not favour AgCl in solution, but in solid state... i.e. a precipitate

Ag+ + Cl- <--> AgCl(s)

addition of Cl- increase left side, so right side must increase as well

Q2

according to this... the reaction must be

blue --> CoCl2

CoCl4 ---> pink, since this is in no presence of Cl- (all has preciptate already)

so...

if we heat --> turns blue

thn

Co(H2O)6]+2 formation is favoured with heat...

pink solution CoCl4-2 only favoured when cold solution

so...

the reaction is endothermic, meaning it requires heat to form [CoH2O)6]+2 ions

Q3

it supports, since heat favours formation of product, meaning that acrcording to le chatelier, this is expected, since the heat favours endothermic reaction

Q4

[CoCl4]-2 + heat --> [CoH2O)6]+2

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