Question

Table 20.2 Half-reaction E° (V) Cr3+ (aq) + 3e- → Cr (s) -0.74 Fe2+ (aq) + 2e- Fe () -0.440 Fe3+ (aq) + e- → Fe2+ (s) +0.771 Sn4+ (aq) + 2e- Sn2+ (aq) +0.154 The standard cell potential (Eºcell) for the voltaic cell based on the reaction below is V. Cr (s) + 3Fe3+ (aq) + 3Fe2+ (aq) + Cr3+ (aq) A) -1.45 B) +2.99 C) +1.51 D) +3.05 E) +1.57

Answer 1

Ans is C +1.51V

Cr(S) + 3Fe³⁺(aq)$\rightarrow$ 3Fe²⁺(aq) +Cr³⁺(aq)

Standard cell potential(E^o_cell): The cell potential when concentration of electrolytes in two half cells are unity( Molarity is 1M) is called standard cell potential.

Here

Reaction at anode is

Cr(s)$\rightarrow$ Cr³⁺(aq)

E^o_Cr³⁺/Cr = -0.74V(Given in data)

Reaction at cathode

Fe³⁺$\rightarrow$ Fe²⁺

E^o_Fe³⁺/Fe²⁺ =+0.771V

E^ocell = E^o_cathode - E^o_anode

=0.771V-(-0.74)V =1.511V