Recitation Activity wit h Electr ochem istry #2 RT nF o RT nF All temperatures a
ID: 695242 • Letter: R
Question
Recitation Activity wit h Electr ochem istry #2 RT nF o RT nF All temperatures are 298K On the previous recitation activity you determined the standard cell potential for a galvanic cell containing aluminum and zinc: 2Al (s) + 32n2. (aq) 2AP. (aq) +3 Zn (s) e-o9ov what is the cell potential after the reaction has reacted to a point where the concentration of zinc ion 0.250M and the concentration of the aluminum ion is 1.500M? 1. A melt of zinc chloride is subject to electrolysis. If 1.00 moles of zinc is to be produced, for how long should the reaction proceed if there is a current flow of 20.0 amps? 2.Explanation / Answer
1) Given
[Al+3] = 1.5 and [Zn+2] = 0.25 M
using the given Nernst equation
E cell = E0 -RT/nF ln K
= E0 - (0.059/n) log K [after substituting the standard values of R =8.314J, T=298K and F = 96500C]
= 0.90 V - (0.059/6) log (1.5)2/(0.25)3
=0.8787V
2) ACCording to Faradays first law
mass of substance deposited w = E it /96500
or w/E = i t/96500
We know mass /equivalent mass(w/E) = number of equivalents
1.0 moles of Zn = 2 equivalents
Thus 2 equivalents = 20 amp x t sec /96500 C
or T = 9650 sec
Thus to deposit 1 mole of Zinc using 20 amp currrent we to pass the current for 9650 sec =160.83 min
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