Download Practical No 11

Practical no 11
IONIC MIGRATION VELOCITY
Experimental setup
Regulated power supply, flat chamber for ionic migration, digital multimeter, digital stopwatch, solutions of
potassium permanganate (KMnO4) and potassium nitrate (KNO3).
Fig. 1 View of the experimental setup
Course of measurements
A. Experimental part
1. Set the flat chamber for ionic migration in the horizontal position precisely using the mounted waterlevel.
2. Connect the power supply to the chamber – positive pole (red connecting cord) to the anode and
negative pole (blue connecting cord) to the cathode. Then connect the chamber to the digital multimeter
using another pair of connecting cords – anode to the positive sign input (red connecting cord) and
cathode to the negative sign input (blue connecting cord).
3. Do the measurements applying the solution of KMnO4 at the concentration of 0,015 [M] and the solution
of KNO3 at the concentration of 0,0025 [M]
A) In order to do the measurements one should cover the groove between the anode and the cathode
applying a small cover plate. Then start to fill the hole at the anode with the KNO3 solution using a
single-use pipette. Because of the capillary effects, filling of the groove towards the cathode will be
started (it is recommended to gently move the cover plate in the direction cathode-anode in order to
accelerate the filling and provide a homogenous distribution of the KNO3 solution in the groove.
Filling of the hole at the anode should be stopped while the KNO3 solution will be reaching the edge
of the hole at the cathode.
CAUTION: The KNO3 solution should NOT be present in the hole at the cathode before the start of
measurements !
Using another pipette fill the hole at the cathode with the KMnO4 solution until it is reaching the
groove between the cathode and the anode (there must be a direct contact between the solutions, if it
is not the case, add the KNO3 solution until the contact is obtained).
B) Set the voltage of 20 [V] on the power supply – check out the value on the digital multimeter.
Permanganate anions will start to migrate in the groove towards the anode in a violet „column”.
While the front of the column is reaching the first scale mark on the chamber for ionic migration,
turn on the stopwatch. Then record the time when the „column” is reaching the next scale marks on
the chamber. Write down the results to the table no 1 in the report’s sheet. After finishing the
measurements turn off the power supply and clean the migration chamber.
4. Perform measurements using sets of solutions as mentioned in the Table no 1. Measure the time of
migration of the front of the column of MnO anions between two neighbouring scale marks on the
migration chamber. Write down the results to the table in the point no 3 in the report’s sheet. The course
of measurement is the same as previously. After finishing the measurements turn off the power supply
and clean the migration chamber.
Number of measurement
KMnO4 [M]
KNO3 [M]
1
0,030
0,0050
2
0,060
0,0100
3
0,120
0,0200
Table no 1. Sets of solutions used in the measurements.
B. Presentation of results
5. Make a plot s = f(t) on the plotting paper. Then, on the basis of the plot, calculate the average ionic
migration velocity.
6. Calculate the mobility of ions (applying the formula from the theoretical part). Write down the result in
the point no 2 in the report’s sheet.
7. Make a plot of the mobility of ions versus the concentrations of solutions u = f(c). Then, on the basis on
the plot, calculate the ionic mobility for an infinite dilution.
8. Calculate the hydrodynamic radius of the permanganate ions (applying the formula from the theoretical
part). Write down the result in the point no 4 in the report’s sheet in the SI units [m], and in [Å].
Required background in theory
1.Uniform linear motion:
a. Definition, parameters of the motion and their units
b. Plots of the displacement and velocity versus time
c. Estimation of an average velocity on the basis of displacement versus time plot
d. Conversion of units of average velocity, for example: mm/s to km/h
2. Description of a motion of a spherical object in a viscous fluid at constant velocity:
a. Frictional force, viscous drag
b. The Stokes law
3. Intensity (E) and potential (U) of the electric field, definition and units of these physical quantities.
Relationship between the intensity and the potential of the electric field.
4. Movement of ions in the electric field:
a. Electric force acting on an ion in the electric field, the formula
b. Explanation of a difference between the average velocity of ion migration and the ionic mobility
c. Derivation of the formula for ionic mobility (u)
d. Definition of ionic mobility at infinite dilution (u0)
e. Method of estimation of the (u0)
f. Derivation of the formula for a hydrodynamic radius of the KMnO4-
Literature:
1. Glasser, „Biophysics”, Springer, 2001.
Medical University in Wrocław
Department of Biophysics
Practical No 11
Ionic migration velocity
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Names of students
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Tutor’s signature
Date
Note
.
1.
Plot the displacement of a front of the column versus time on a plotting paper.
Position
Distance [cm]
Time [s]
Average velocity of the ionic migration:
2.
Mobility of the ions for c = 0,015 [M]:
3.
Plot the ionic mobility [u] versus the concentration of KMnO4 solution on a plotting paper.
KMnO4 concentration [M]
0,03
0,06
0,12
Time [s]
Ionic mobility at infinite dilution [u0]:
4.
[m]
[Å]
Hydrodynamic radius of the ions [R]:
Viscosity of water [η] = 1,009 ∙ 10 [ ∙ ∙
Elementary charge [e] = 1,602 ∙ 10 [ ∙ ]
]
u [cm2V-1s-1]