Electrochemistry for Energy Materials SS2013

Electrochemistry for Energy Materials SS2013
Hubert Gasteiger, Tom Nilges, Moniek Tromp
30/Apr/2013 – Sheet 2
Julien Durst, Thomas Mittermeier
Exercise 1:
In a conductivity cell an aqueous solution of 0.1 M HClO 4 is contained. The hereby
measured resistance is 12 Ω. The molar conductivity of HClO 4 is 418 S cm 2 mol -1 . Now, a
KNO 3 solution of unknown concentration is measured in the same cell with a resulting
resistance of 6.9 Ω. Calculate the concentration of KNO 3 (the molar conductivity of KNO 3 is
145 S cm 2 mol -1 ).
Exercise 2:
At infinite dilution, the following molar conductivities are given [1] and references therein:
substance [cm 2 S mol -1 ]
KOH 272
KCl 150
NaCl 126
1. Calculate the molar conductivity of Na + and OH - at infinite dilution if .=
76 cm 2 S mol -1 .
2. Calculate the molar ionic conductivities at a concentration of 0.01 M NaOH in
aqueous solution (assume a Kohlrausch constant of 3162 cm 7/2 S mol -3/2 ). Further,
the mobility of the Na + and OH - ions.
3. A potential difference of 1.1 V is applied between two plates separated by 1 cm in
the solution. Find the current density and the drift speed of each ion.
[1] A.J. Bard, L.R. Faulkner, Electrochemical Methods (2 nd edition).
Exercise 3:
Suppose one wants to determine the contribution of electronic (as opposed to ionic)
conduction through doped AgBr, a solid electrolyte. A cell is prepared with a film of AgBr
between two Ag electrodes, each of mass 1.00 g, that is, (-)Ag/AgBr/Ag(+). After passage of
200 mA through the cell for 10.0 min, the cell was disassembled and the cathode was found
to have a mass of 1.12 g. If Ag deposition is the only faradaic process that occurs at the
cathode, what fraction of the current through the cell represents electronic conduction in
AgBr
1 Exercise 2 „Elektrochemie für Energiematerialien“ SS2013 30/Apr/2013

Exercise 4:
Transference numbers are often measured by the Hittorf method as illustrated in this
problem. Consider the three-compartment cell:
L С R
(-)Ag/AgNO 3(0.100 M)//AgNO 3(0.100 M)//AgNO 3(0.100 M)/Ag(+)
where the double slashes (//) signify sintered glass disks that divide the compartments and
prevent mixing, but not ionic movement. The volume of AgNO3 solution in each
compartment (L, C, R) is 25.00 ml. An external power supply is connected to the cell with
the polarity shown, and current is applied until 96.5 С have passed, causing Ag to deposit
on the left Ag electrode and Ag to dissolve from the right Ag electrode.
1. How many grams of Ag have deposited on the left electrode How many mmol of Ag
have deposited
2. If the transference number for Ag + were 1.00 (i.e., t Ag+ = 1.00, t NO3- = 0.00), what
would the concentrations of Ag + be in the three compartments after electrolysis
3. Suppose the transference number for Ag + were 0.00 (i.e., t Ag+ = 0.00, t NO3- = 1.00),
what would the concentrations of Ag + be in the three compartments after
electrolysis
4. In an actual experiment like this, it is found experimentally that the concentration of
Ag + in the anode compartment R has increased to 0.121 M. Calculate t Ag+ and t NO3.
2 Exercise 2 „Elektrochemie für Energiematerialien“ SS2013 30/Apr/2013