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The measured voltage in a Zn-H cell is 0.45 V at 25°C when IZn*21 is 1 M. What is the concentration of H? 0592 E-E- 1g a Q =
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Answer #1

Anode Reaction : Zn ----> Zn2+ + 2e- ; E0 = 0.76 V

Cathode Reaction 2H+ + 2e - ------ > H2 ; E0 = 0.00 V (SHE)

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Cell Reaction : Zn (s) + 2H+ (aq) ------- > Zn2+ (aq) + H2 (g) ; E0cell = 0.45 + 0.00 = 0.76 V

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Applying Nerns't Equation :

Ecell = E0Cell - 0.059 / n log [Zn2+] / [H+]^2

(n = number of electron transferred ; n =2 in this case)

0.45 = 0.76 - (0.059/2) log [1] / [H+]^2

-0.31 = -0.03 * log 1/ [H+]^2

-0.31 / -0.03 = log 1/ [H+]^2

10.3 = log 1/ [H+]^2

1/ [H+]^2 = 1010.3

On solving [H+] = 7.1 * 10-6

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