Multiple choice

Calculate the minimum concentration of Ag+ that would remain unreduced by a standard Fe2+/Fe3+ electrodes at equilibrium?

Given Fe3+ + e- → Fe2+ + 0.671 v Ag+ + e- → Ag + 0.699 v

  1. 0.335 M

  2. 0.435 M

  3. 0.235 M

  4. 0.135 M

  5. 0.535 M

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A Correct answer
Explanation

The cell reaction is Fe2+ (aq) + Ag+ (aq) → Fe3+ (aq) + Ag (s)Eo cell = Eo Fe2+ → Fe3+ + E Ag+ → Ag (s)Eo cell = (- 671) + (0.699)Eo cell = + 0.028 vEo cell = 0.059/n log (Fe3+ x Ag)/(Fe2+ x [Ag+]) Now Eo cell = 0.028 vn = 1, [Fe3+] = [ Fe2+] = 1 M, [Ag+] = ? 0.028 = 0.059/1 log (1 x 1)/(1 x [Ag + ]) 0.028/0.059 = log 1/([Ag+])log 1/([Ag+]) = 0.4745log 1/([Ag+]) = 100.4745 = 2.98 [Ag+] = 1/2.98 = 0.335 M.