For almost any aqueous chemical system there are always two or more equilibrium

Question

For almost any aqueous chemical system there are always two or more equilibrium occurring concurrently. Each separate equilibrium can be described with a balanced equation, an equilibrium constant and the Law of Mass Action expression.

(a)What must be true at the equilibrium condition for each and every Law of Mass Action expression for any given equilibrium system?

(b)For the two aqueous equilibrium system below (parts i and ii), the identity of the original chemicals added to the system are listed. Analyze each system and list below:

I. The symbol (ex:Ksp) for all the equilibrium constants applicable to each system

II. The value of each Keq

III. The equilibrium expression (Law of Mass Action), and

IV. Identify every separate chemical species that is present in each system in each system whether that species be ions, molecules, or precipitates (Remember when analyzing each system that there are many types of equilibrium that have been studied in these last two chapters: Kw, Ka, Kb, Ka's for poly - acids, Kb, Ksp, K.....)

(i) Starting chemicals: ammonium hydroxide, zine nitrate (five Keq's and ten separate chemical species)

(ii) Starting chemicals: carbonic acid and nickel(II) nitrate (five Keq's and ten seperate chemical species)

Explanation / Answer

(i)

(1)

NH4OH   <--------------------->   NH4+ (aq) + OH- (aq)

Kb = [NH4+][OH-]/[NH4OH]

(2)

Zn+ 2 (aq)   + 2 NO3 - (aq) ---------------------> Zn(NO3)2 (aq)

Kf = [ Zn(NO3)2 ]/[ Zn(NO3)2 ][NO3 -]^2

(3)

2 NH4OH (aq) + Zn(NO3)2 (aq) -----------------------> Zn(OH)2 (s) + 2NH4NO3(aq)

Keq = [NH4NO3]^2/ [NH4OH][Zn(NO3)2]

4)

Zn(OH)2 (s) ---------------------->Zn+2 + 2 OH-

Ksp = [Zn+2][OH-]^2

(ii)

H2CO3 <---------------------> H + HCO3 -

Ka1 = [HCO3 -][H+]/[H2CO3]

HCO3-   <--------------------> CO3^-2   + H+

Ka2 = [CO3 -2][H+]/[HCO3-]

NiNO3 + H2CO3 -------------------------> NICO3 + HNO3

NiCO3 ----------------------> Ni+2 + CO3^-2

Ksp = [Ni+2][CO3-2]

these are all possible equilibriums

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