72) A voltaic cell is constructed with two silver-silver chloride electrodes, wh

Question

72) A voltaic cell is constructed with two silver-silver chloride electrodes, where the half-reaction is AgCl (s) + e- Ag (s) + Cl-(aq) E= +0.222 V The concentrations of chloride ion in the two compartments are 0.0100 M and 1.55 M, respectively At 25 °C, the cell emf is A) 0.216 B) 0.130 C) 0.00143 D) 34.4 E) 0.228 V. 73) The standard emf for the cell using the overall cell reaction below is +0.48 V: Zn (s) + Ni2+ (aq) Zn2+ (aq) + Ni (s) f generated by the cell when [NPY-0.100 M and [Zn2+] 225 M is

Explanation / Answer

Anode :            Ag + Cl- ==> AgCl + e-     Eo = -0.222 V
Cathode:            AgCl + e- ==> Ag + Cl-     Eo = +0.222 V
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Overall reaction : Ag + Cl-(anode) + AgCl ==> Ag + Cl-(cathode) + AgCl    Eo cell = +0.00 V

Due to the differences in Cl- ion concentration we get the volatge, which can calculate using
the Nernst equation:

E cell = Eo cell - 0.059/n log Q
       = 0.00 V - 0.059/1 log ([Cl- cathode] / [Cl- anode])
       = - 0.059 log(0.01 M/1.55 M)
       = 0.129 V
E cell = 0.130 V

Hence the answer is : B (0.130 V )

Given overall reaction : Zn(s)+Ni2+(aq)Zn2+(aq)+Ni(s) Ecell = + 4.8 V

E cell = Eo cell - 2.303 RT/nF log[Zn+]/[Ni+2]
       = Eo cell - 0.059/n log[Zn+2]/[Ni+2]
       = + 4.8 -0.059/2 log(2.25M/0.1M)
       = 4.76 V
     
Hence, the answer is : 4.76 V

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