Determination of cell constant

Conductometry

1. SHREE MALLIKARJUN COLLEGE CLASS: SYBSC
Dr. Mithil Fal Desai
Aim: Determination of cell constant.
Chemicals: Potassium chloride.
Apparatus: Beakers, standard flask and glass rod.
Instrument: Conductivity cell
Theory: Conductivity (mho or ohm
-1
) of any solution depends on the nature of ions present in it.
The specific conductance is measure of conductance of solution with electrodes of unit area that
are place 1 cm apart. The specific conductance (K) is given by
K = (1/R) (l/a) as 1/R = C i.e. conductance
K = C (l/a)
l/a = K/C as l/a is constant called as ‘cell constant’
Cell constant = Specific conductance (ohm
-1
cm
-1
) / measured conductance (ohm
-1
)
Thus, the unit of cell constant is cm
-1
.
Procedure:
i) Calibrate the conductivity cell
Refer the instrument manual.
ii) Preparation of 0.1 M and 0.01N KCl solution
Prepare 0.1 N KCl by dissolving _____g in 100 mL distilled water. Pipette out 10 mL of 0.1 N
KCl and dilute to 100 mL to prepare 0.01N KCl solution
iii) Measuring conductance.
a) Measure the conductance of distilled water.
b) Dip the conductivity cell in 40 mL 0.1N KCl and record the conductance observed. Note down
the temperature. Wash the conductivity cell with distilled water and measure the conductance
for 0.01 N KCl. Tabulate the readings in Table 1.
Observations:
Room temperature =____ ◦C.
Conductance of distilled water ‘A’=______ ohm
-1
.
Table 1
Concentration of
KCl
Specific
conductance
(mohm
-1
cm
-1
)
Measured
conductance
(ohm
-1
)
‘B’
Observed
conductance
(ohm
-1
)
= B - A
Cell constant
(cm
-1
)
0.1 12.88
0.01 1.413
Result: Cell constant =______ cm
-1
.
Further Reading
Experiments in Applied Chemistry, S. Rattan, S. K Kataria and Sons.