Question

Use the following notation for an electrochemical cell for Parts (I) – (III):
           
                        Al(s)|Al³⁺(aq) | | Ag¹⁺ (aq) |Ag(s)

(I). What is the balanced equation for the cell reaction? (Choose the correct letter)

A. Al(s) + Ag1+(aq) ---> Ag(s) + Al3+(aq)	C. Al(s) + 2Ag1+(aq) ---> 2Ag(s) + Al3+(aq)
B. 2Al(s) + 3Ag1+(aq) ---> 3Ag(s) + 2Al3+(aq)	D. Al(s) + 3Ag1+(aq) ---> 3Ag(s) + Al3+(aq)

(II). How many moles of electrons are transferred during the cell reaction above? (Choose the correct letter)   
                                             

A.    6 mol

B.    5 mol

C.    3 mol

D.    2 mol

(III). The E^o_cell for the reaction is 2.46 V. The approximate value of the equilibrium constant K_c at 25°C is (Choose the correct letter)
              

A.    10166

B.    10125

C.    1058

D.    1044

Answer 1

(I) The cell notation is:

Al(s)|Al3+(aq) | | Ag1+ (aq) |Ag(s)

The balanced cell reaction is shown below.

Al(s) + 3 Ag⁺(aq) ---------> Al³⁺ (aq) + 3Ag(s)

(II) Option (C) is the correct answer. 3 moles of electrons are lost by Al and 3 moles of electrons are gained by 3 moles of Ag+, 1 mole of electron by each Ag+ ion.

(III) At 25oC

E^o_cell = (RT /nFR) lnK

n = number of electrons involved in balanced redox rxn, n =3

lnK = (E^o_cell X n X F / RT)

logK =  2.46​ X 3 X 96500 / 8.314 X 298K X 2.303 = 124.81

K = 6309 X 10¹²⁴.