Consider the following electrochemical cell : Pt | O _ 2 ( ~g )(1 bar ) | HCl ( aq ) \| M ^ 2+ ( aq , 1.0 M ) M ( ~s ) The pH above which, oxygen gas would start to evolve at anode is \_\_\_\_ (nearest integer). [ array ll Given: & E ^ o _ M ^ 2+ / M =0.994 ~V \\ & E ^ o _ O _ 2 / H _ 2 O =1.23 ~V array \ standard reduction potential ]
A. A
In this electrochemical cell, at the anode oxygen evolution occurs from water oxidation. Using Nernst equation for the O₂/H₂O couple: E_ anode = E°_ O_2/H_2O - 0.059 4 1 [H^+]^4 = 1.23 - 0.059 pH At the cathode: E_ cathode = 0.994 V (standard potential for M²⁺/M reduction) For oxygen to start evolving, the cell potential becomes zero: E_ cell = E_ cathode - E_ anode = 0 0.994 = 1.23 - 0.059 pH 0.059 pH = 0.236 pH = 4.0
Related: Chemistry — Electrochemistry · All PYQ Banks