The Standard Reduction potential at 25°C for ( MnO ₄)⁻¹/ H ^+ is +1.49 V. The E^0 values for four redox couples: (a). Co ³⁺/ Co ²⁺ , (b). Cr ³⁺/ Cr , (c). Au ³⁺/ Au and (d). Ag ^+/ Ag are +1.81 V, –0.74 V, +1.50 V and +0.8 V respectively. Identify the two reduced species which cannot be oxidised by ( MnO ₄)⁻¹/ H ^+

Step-by-step solution

(MnO₄)^-/H^+ has E° = +1.49 V. It can only oxidise species whose E° is less than +1.49 V. Species with E° > +1.49 V cannot be oxidised by permanganate: Co³⁺/Co²⁺ : E° = +1.81 V > +1.49 V cannot be oxidised Au³⁺/Au : E° = +1.50 V > +1.49 V cannot be oxidised Cr³⁺/Cr : E° = -0.74 V Ag^+/Ag : E° = +0.8 V The two species that cannot be oxidised are (a) and (c).