Reference Electrodes The E degree value for the following reaction is 0.446 V re

Question

Reference Electrodes The E degree value for the following reaction is 0.446 V relative to the standard hydrogen electrode (SHE): Ag2CrO4(s) + 2e- rightarrow 2Ag(s) + CrO42-(aq) A chemist wishes to determine the concentration of CrO42' electrochemically. A cell is constructed consisting of a saturated calomel electrode (SCE; which has a reduction potential of 0242 V relative to the SHE) and a silver wire coated with Ag2CrO4 and suspended in a CrO42- solution. What is the potential of this cell at 25 degree C when [CrO42] = 1.00 M? 0.204 V Calculate Delta G for the full-cell reaction at 25 degree C when [CrO42-] = 1.00 M? What is the potential of this cell at 25 degree C when [CrO42] =4.80 times 10-5 M? For a solution of unknown [CrO42-], the measured potential for the cell at 25 degree C is 0.361 V. What is [CrO42-] (in mol/L)?

Explanation / Answer

We Know that :       The given Reaction is :       Ag2CrO4 (s) + 2e --------> 2Ag (s) + CrO4-2       The E0 value for theabove reaction is 0.446 V         G = - n FE0              = -2 x 96500 J / V x 0.204 V               = - 39372 J               = -39.372 kJ               = -39.372 kJ       E cell = E0 - 0.059 / 2 log [CrO4-2 ]                  = 0.204 V - 0.059 / 2 log [ 4.80 x 10-5]                  =    0.33140 V        Ecell = E0 - 0.059 / 2log [ CrO4-2 ]       0.361 V = 0.204 V - 0.059/2 log [ CrO4-2 ]         [CrO4-2 ] = 0.000004763 M                            = 4.763 x 10-6 M        Ecell = E0 - 0.059 / 2log [ CrO4-2 ]       0.361 V = 0.204 V - 0.059/2 log [ CrO4-2 ]         [CrO4-2 ] = 0.000004763 M                            = 4.763 x 10-6 M

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