ive been using the nersnt ewuation to no avail. i put .2/.8 in place of Q since

Question

ive been using the nersnt ewuation to no avail. i put .2/.8 in place of Q since i though it was products over reactants and it seemed that the anode would be the product in this relationship. im stuck. please help

19. A voltaic cell with Ni/Niir (Es -0.25V) and Coco as anode (E, -0.28 V has e following concentrations 030 Mi 0.20 M. Calculate the initial Eca. A) 0.0378 V B) 004 V C) 0.06 V D) 0.05 V 20. Calculate Eo and indicate whether the overal reaction shown is spontaneous or Half-reaction 0.53 V -0,74 V Overall reaction: 2Cr(s) +3 +2Crit (aq) +6l (aq) A) E cell 27 V spontaneous B) E cen 27 V, nonspontaneous Epeen .27 V. spontaneous D Eocell 1.27 V,nonspontaneous

Explanation / Answer

19) the reaction is Ni2+ (aq) + Co (s) <---> Ni (s) + Co2+ (aq)

Q = [Co2+]/ [Ni2+] = 0.2 /0.8 = 0.25

Eo cell = Eo cathode - Eo anode

   = -0.25 - (-0.28) = 0.03

Nernest equation is E cell = Eo cell - ( 0.059/n) log Q    where n = number of e- transferred per reaction = 2

E cell = 0.03 - ( 0.059/2) log ( 0.25)

      = 0.0477     ( rounded value is )

      = 0.05 V

20) Eo reaction = Eo ( reudction half) - Eo ( oxidation half)

           = Eo ( I2/I-) - Eo ( Cr3+/Cr)

       = 0.53 - (-0.74)

       = 1.27

Eo cell = 1.27 , reaction is spontanoeus                ( when Eo cell > 0 reaction is sponatneous)

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