First slide

Electrochemical cells

Question

For the cell prepared from electrode A and B;
$Electrode A : {Cr}_{2} O_{7}^{2 -} ∣ {Cr}^{3 +}, E_{red}^{\circ} = + 1.33 V and$
$Electrode B : {Fe}^{3 +} ∣ {Fe}^{2 +}, E_{red}^{\circ} = 0 .77 V$
Which of the following statements is/are correct ?

Moderate

A

The electrons will flow from B to A when connection are made
B

The EMF of the cell will be 0.56V
C

A will be positive electrode
D

All of these

Solution

$E_{{RP}_{{Cr}_{2} O_{7}^{2 -} / {Cr}^{3 +}}^{\circ}}^{2 +} = 1 .33 V and E_{{RP}_{{Fe}^{3 +} / {Fe}^{2 +}}^{\circ}}^{2 +} = 0 .77 V$
$∴ E_{{op}_{{Fe}^{+ 2} | Fe}}$ is more thus it will oxidise or electron will
flow from Fe electrode to Cr electrode. Also Fe electrode will be negative. Also,
$E_{cell}^{o} = E_{{OP}_{Fe}}^{0} + E_{{RP}_{Cr}}^{0} = - 0 .77 + 1 .33$

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