CHEM3370 Physical Chemistry II
Electrochemistry Tutorial #1 – for week #3: 03-07/02/2020
1.
In order to determine the molar conductivity of a 0.0500 M solution of AgNO3, the
solution’s resistance was measured in a conductivity cell and it was found that R = 75.8 Ω.
In the same cell, a 0.0200 M KCl solution had a resistance of 157.9 Ω. Given that the
accepted molar conductivity of the KCl solution is 0.013834 S m2 mol¯1.
a)
Calculate the cell constant.
b)
Calculate the molar conductivity of the AgNO3 solution.
2. For a certain strong electrolyte, Λm is found to be 0.00786 and 0.00839 S m2 mol-1 for a
0.0200 M and a 0.00500 M solution respectively. What is the value of the limiting molar
conductivity, Λm°, for this electrolyte?
3. The molar conductivities at infinite dilution of NaCl, NaNO3, AgNO3, HCl and NaAc are
126.5, 121.6, 133.4, 426.0 and 91.0 S cm2 mol¯1 respectively at 298K.
4.
a)
Calculate the molar conductivities at infinite dilution for AgCl and HAc at 298K.
b)
The molar conductivity of 0.00500 M acetic acid (HAc) was found to be 22.9 S cm2
mol-1. What is the Ka of acetic acid at this concentration and 298K?
Calculate the contribution of the conductivities of the individual ions in a H 2SO4 solution
when its limiting molar conductivity is 0.0859 S m2mol¯1 and the transport number for H+
is 0.814.
5. For a solution of 2.0 x 10¯4 mol kg¯1 MgCl2
6.
i)
Calculate the ionic strength, I, of the solution.
ii)
Calculate the mean ionic activity coefficient using the Debye-Hückel Limiting Law,
log γ± = -A |z+ z−|√I where A = 0.509.
iii)
Calculate the activity of the Cl- ions in the solution.
The transport number of the sodium ion in 0.0200 M NaCl at 25°C was determined by the
moving boundary method and the following data were obtained.
L/cm
t/s
0.00
0
1.00
344
6.00
2070
10.00
3453
The cathode was Ag |AgCl and the anode Cd. The cross-sectional area of the tube was
0.1115 cm2. The current was 0.001601 amp. Calculate the transport number of the sodium
ion under these conditions.