An electrochemical cell consists of a standard hydrogen electrode and a copper metal electrode. What is the potential of the cell at 25 °C if the copper electrode is placed in a solution in which [#Cu^(2+)#] = #2.5 x 10^-4# M)?

Question

The copper electrode is placed in a solution of unknown #Cu^(2+)#. The measured potential at 25°C is 0.195 V. What is #Cu^(2+)#? (Assume #Cu^(2+)# is reduced)

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Answer 1 · 2017-03-05T17:26:43

#sf((a))#

#sf(+0.23color(white)(x)V)#

#sf((b))#

#sf(1.25xx10^(-5)color(white)(x)"mol/l")#

#sf((a))#

The 1/2 cell in question is:

#sf(Cu_((aq))^(2+)+2erightleftharpoonsCu_((s))" "E^@=+0.34color(white)(x)V)#

The potential of the 1/2 cell at #sf(25^@C)# is given by:

#sf(E=E^(@)+0.05916/(z)log([["ox"]]/[[red]))#

#:.##sf(E=E^@+0.05916/(z)log[Cu_((aq))^(2+)])#

#sf(z)# is the number of moles of electrons transferred which, in this case, is 2.

#:.##sf(E=+0.34+0.05916/(2)log[2.5xx10^(-4)])#

#sf(E=+0.34+(0.02958xx-3.602)color(white)(x)V)#

#sf(E=+0.233color(white)(x)V)#

#sf((b))#

Here the electrode is being used to estimate concentration.

#sf(0.195=+0.34+0.05916/(2)log[Cu_((aq))^(2+)])#

#:.##sf(log[Cu_((aq))^(2+)]=-0.145/0.02958=-4.9012)#

#sf([Cu_((aq))^(2+)]=1.25xx10^(-5)color(white)(x)"mol/l")#