verification of debye-hÜckel-onsager equation
TRANSCRIPT
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CL 201 Date : Batch: ……..……...
Name : ………………………………….. Roll No.: …………..
EXPERIMENT 9
VERIFICATION OF DEBYE-HÜCKEL-ONSAGER EQUATION
FOR STRONG ELECTROLYTES
AIM
To verify the Debye-Hückel-Onsager equation λc = λo – (A + B λo)√c
for a strong uni-univalent electrolyte (KCl).
THEORY
Solutions of electrolytes (acids, bases and salts in water) conduct
electricity. In these solutions, the passage of electric current is due to
the migration of cations and anions in opposite directions.
It is the valence, migration velocity and the concentration of the ions
which determine the strength of the current flowing through a
solution of an electrolyte.
According to the Arrhenius theory, strong electrolytes (KCl, NaCl)
dissociate completely at all dilutions.
The increase in the molar conductance of solutions of strong
electrolytes, with dilution, is mainly due to the increased mobility of
the ions. Increase in dilution results in a decrease of inter ionic
interactions, thereby increasing the migration speed of the ions, and
hence the equivalent conductivity.
The conductance behavior of strong electrolytes has been given by
the Debye-Hückel-Onsager equation λc = λo – (A + B λo) √c ,
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where λc is the equivalent conductivity at concentration c ,
λo is the equivalent conductivity at infinite dilution,
A and B are the Debye – Hückel – Onsager coefficients.
At 25oC , the values are A = 60.2 , and B = 0.229 .
A plot of λc (y - axis) against √c (x - axis) should be linear,
with a slope = – (A + B λo).
The intercept on the y-axis would give λo .
Hence, λo can be obtained by extrapolating the graph to zero
concentration.
MATERIALS REQUIRED
Conductometer (with cell), pipettes, beakers, KCl, volumetric flasks.
PROCEDURE 1. Prepare a stock solution of 0.1 N KCl solution by exact
weighing.
2. Standardize the conductometer using this 0.1 N KCl solution.
3. Measure the conductance of the 0.1 N KCl solution.
4. Dilute the stock solution of 0.1 N KCl, so as to obtain
solutions of the following concentrations of KCl :
0.05 N ; 0.025 N ; 0.0125 N ; 0.00625 N ; 0.00312 N .
5. Measure the conductance of each solution prepared in Step 4.
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OBSERVATIONS Room Temperature = …….. oC Table 1. Conductivity of KCl solutions ____________________________________________________________
Sl. No. Concentration √c specific conductance
of KCl (N)
(c) ____________________________________________________________
1 0.10 2 0.05 3 0.025 4 0.0125 5 0.00625
6 0.00312 ____________________________________________________________
CALCULATIONS AND GRAPH
Plot a graph of λc (y - axis) against √c (x - axis).
Extrapolate to C = 0
Calculate the value of the Slope and the Intercept.
Comment on the values obtained.
RESULTS