Calculate the potential:

Problem:

Calculate the potential for the cell given below:

Answer:

Reaction for this cell can be written as:

1(Cr₂O ^2-₇+ 14H⁺   +  6e → 2Cr³⁺   +  7H₂O)

6(Fe²⁺ → Fe³⁺ +le)

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Cr₂O^2-₇ + 14H⁺ + 6Fe²⁺ → 2Cr³⁺ +6Fe³⁺ + 7H₂O

Cell potential :

E_cell = E_Cr2O7^2- / _Cr³⁺ - E_Fe³⁺_/Fe²⁺

Ecell ={E_Cr2O7^2- / _Cr³⁺ - (0.0591/6) log[Cr³⁺]²/[Cr₂O₇^2-][H+]12}- { E_Fe³⁺_/Fe²⁺ -(0.0591/6) log{[Fe²⁺]}/{[Fe³⁺]}

Substitute the values of standard potentials from Table 1, Appendix A, concentrations:

E_cell = {1.33 - 0.0591/6 log [0.005]² / [0.020][0.010]¹⁴} - {0.771 - (0.0591/1) log {[0.010]}/[0.001]}

E_cell = 1.33  - 0.109 - 0.771 + 0.0591  =  0.509 V