Final answer:
Oxygen will not oxidize [Co(H2O)6]2+ or [Co(NH3)6]2+ to the corresponding cobalt(III) complexes under standard conditions because their oxidation potentials are less positive than the potential required for oxygen evolution.
Step-by-step explanation:
To determine whether the complex ions [Co(H₂O)6]2+ and/or [Co(NH3)6]2+ can be oxidized to the corresponding cobalt(III) complex by oxygen, we need to compare the standard reduction potentials of these complexes with the standard reduction potential for the oxidation of water to oxygen, which is a competing reaction that occurs at +1.229 V under standard conditions. The reaction for the production of oxygen is:
O₂(g) + 4H+(aq) + 4e- → 2H₂O(l) (E° = +1.229 V)
Oxidation of [Co(H₂O)6]2+ and [Co(NH3)6]2+ involve the removal of an electron to form [Co(H₂O)6]3+ and [Co(NH3)6]3+, thus their provided reduction potentials need to be inverted:
[Co(H₂O)6]3+(aq) + e- → [Co(H₂O)6]2+(aq) (E° = +1.8 V) becomes E° = -1.8 V for oxidation.
[Co(NH3)6]3+(aq) + e- → [Co(NH3)6]2+(aq) (E° = +0.1 V) becomes E° = -0.1 V for oxidation.
Since the cell potentials for oxidation of [Co(H₂O)6]2+ and [Co(NH3)6]2+ are -1.8 V and -0.1 V respectively, which are both less positive than the potential for the oxidation of water to oxygen, it implies that oxygen will not oxidize these Co(II) complexes to Co(III) under standard conditions. Oxygen can oxidize other species with oxidation potentials more positive than +1.229 V.