Question

The standard emf for the cell using the overall cell reaction below is +2.20 v: 2al(s) + 3i2(s) → 2ai3+(aq) + 6i-(aq) the emf generated by the cell when [ai3+] = 3.5 × 10-3 m and [i-] = 0.015 m is ________ v.

Answer 1

Following reactions are involved in above electrochemical cell:

At Anode:           2Al                 →      Al3+         +      6e-
At cathode:       3I2  +  6e-       →    6I-
Net Reaction:  2Al(s) + 3I2(s)   →  2Al3+(aq) + 6I-(aq)

Net electron involved in above reaction = n = 6

Given: Eo cell = 2.20 v

From Nerst equation, we have
Ecell = Eo cell - $\frac{RT}{nF}log( \frac{1}{[Al3+]^2[I-]^6) }$
         =  2.20 - $\frac{8.314X298}{6X96500}log( \frac{1}{[3.5 × 10-3 ]^2[0.015]^6) }$
         =  2.1755 v

Thus, EMF generated by cell = 2.1755 v