Question

A12a The cell Ag //AgCl (sat'd), KCI (1.00 M) //NiL2 (0.0250 M), NL (0.150 M) //Ni has a voltage of -0.767 V. What is the overall formation constant of NIL ? Given: AgCl(s) + Ag(s) + CHE = +0.222 V Ni2+ + 2e Ni(s) Eo = -0.257 V A12b Consider the following standard reduction potential: Ag+e Ag() Eo = +0.800 V Agl(s) + Ag(s) + I EO = -0.164 V Calculate the solubility constant, Ksp at 250C for Agl. Agl(s) Ag+ (aq) + (aq).........--Section Break (Next Page)--

A12a The cell
Ag //AgCl (sat’d), KCl (1.00 M) //NiL2 (0.0250 M), NaL (0.150 M) //Ni
has a voltage of -0.767 V. What is the overall formation constant of NiL2?
Given:

AgCl(s) + e Ag(s) + Cl- Eo = +0.222 V Ni2+ + 2e Ni(s) Eo = -0.257 V
A12b Consider the following standard reduction potential:
Ag+ + e Ag(s) Eo = +0.800 V AgI(s) + e Ag(s) + I- Eo = -0.164 V
Calculate the solubility constant, Ksp at 25oC for AgI.
AgI(s) Ag+ (aq) + I- (aq)

Answer 1

A12a.

Ag //AgCl (sat’d), KCl (1.00 M) //NiL₂ (0.0250 M), NaL (0.150 M) //Ni
Ecell = -0.767 V.
Given:

AgCl(s) + e $\rightleftharpoons$ Ag(s) + Cl^- Eo = +0.222 V

Ni²⁺ + 2e    $\rightleftharpoons$ Ni(s) Eo = -0.257 V

Complex formation reaction :    Ni²⁺ + 2L    $\rightleftharpoons$ NiL₂

E^ocell = E_R -E_L = -0.257 V -0.222 V = -0.479 V (at 25 C)

Ecell =  -0.767 V. = -0.479 V - (0.0591/2 ) log ((Ni(s) ( AgCl(s))2 / (Ag(s)²(Cl^-)²(Ni²⁺))

activity for soild =1;   (Cl^-) = 1.00 M

Ecell =  -0.767 V. = -0.479 V - (0.0591/2 ) log (1 / (Ni²⁺)) = -0.479 V + (0.0591/2 ) log (Ni²⁺)

or log (Ni²⁺) = -9.75 or   (Ni²⁺) = 1.78*10^-10 M

Complex formation reaction :    Ni²⁺ + 2L    $\rightleftharpoons$ NiL₂

So, overall formation constant (Kf) =

Kf = ( NiL₂ ) / (Ni²⁺) (L-)² =  (0.0250 ) / (1.78*10^-10 ) (0.150)²  = 6.24*10⁹

12 b.

Given:

Ag+  + e $\rightleftharpoons$ Ag(s)     Eo = +0.800 V

AgI (s)  + e    $\rightleftharpoons$ Ag(s) + I^- Eo = -0.164 V

overall reaction :  AgI (s)   $\rightleftharpoons$ Ag+ (aq) + I^- (aq)

E^ocell = E_R -E_L = -0.164V - 0.800 V = -0.964 V (at 25 C)

Ecell    = -0.964 V - (0.0591/1 ) log ((Ag⁺) (I^-))

activity for soild =1

at equilibrium, Ecell    = -0.964 V - (0.0591/1 ) log ((Ag⁺) (I^-)) = 0.0

log (Ag⁺) (I^-) = -0.964 V / 0.0591V = -16.3

or Ksp (AgI) = (Ag⁺) (I^-) = 5.02*10^-17