Chemistry pdf specific conductance download

2. Electrolytic Conductance
Metallic and electrolytic conductors obey ohm's law according to which
the resistance of a conductor is the ratio of the applied potential
difference (V) to the current (I) flowing.
R=
V
I
Where,
R is expressed in ohms.
Units of R = ohm, ??????

3. Conductance (C)
The conductance of a conductor is equal to reciprocal of resistance.
C=
1
R
Where,
C is expressed in mho or ohm
–1
or Siemen (S).

4. Specific resistance (??????)
The resistance (R) of a conductor of uniform cross section is directly
proportional to its length� and inversely proportional to its area of
cross section (A). It is also known as resistivity.
R∝
�
A
R=ρ
�
A

5. Where, ?????? is a constant and called resistivity or specific
resistance.
When l = 1 , A = 1 , then ?????? = R thus the specific resistance may be
defined as the resistance of a conductor of unit length and unit
area of cross section.
Unit of ?????? is ohm - cm

6. Specific conductance or Conductivity (k, kappa)
It is defined as the reciprocal of specific resistance it is also known as
conductivity.
k=
1
ρ
Units of “k” = ohm
–1
m
–1
or S m
–1
or S cm
–1
The above definitions apply to metallic conductors and electrolytes.

7. Specific conductance or Conductivity (k, kappa)
In the case of solution of electrolytes, the resistance offered by
the solution to the flow of current is,
(i) Directly proportional to the distance between the electrodes
R∝�

8. (ii) Inversely proportional to the area of cross section of the
electrodes
R∝
�
A
R=??????
l
A
The conductance
C=
A
ρ�

9. The conductance
C=
A
ρ�
Since
k=
1
ρ
So k=C×
�
A
If � = 1 cm , A = 1 cm
2
then ?????? = C
Hence specific conductance of a solution is defined as the
conductance of one centimetre cube of the solution of the
electrolyte.

10. k=C×
�
A
Where, (� /??????) = Cell constant
Cell constant (x) is a fixed quantity for a particular cell and is
defined as the distance between two parallel electrodes of a cell
divided by the area of cross section of the electrodes.
k=C×cell constant
????????????�� ??????����??????��=
�
??????
= � R = Specific conductance × resistance
Unit of ?????? is ohm
-1
cm
-1

11. Equivalent Conductivity / Equivalent Conductance (λ
eq , Λ
eq)
It is defined as the product of specific conductance ( ?????? ) and the
volume (V in ml) of the solution which contain one gram
equivalent of the electrolyte.
λeq =� × Vml
If concentration of solution is C - gram equivalent per litre then
λeq=
??????×1000
N
Unit of λeq : ohm
-1
cm
2
per gram equivalent

12. Molar Conductivity/Molar Conductance(λ
m or Λ
m )
It is defined as the product of specific conductance (??????) and the
volume (V in ml) which contains one mole of the electrolyte.
λm= ??????×V
ml
λm=
κ ×1000
Molarity
Unit→ohm
-1
cm
2
permole

13. and
Or
So
Relation between λ
eq and λ
m
λm=
κ ×1000
M
λeq=
κ ×1000
N
Normality = Valency Factor × Molarity
N=n×M
λeq=
λ�
V.F.

14. Example
Solution
The molar conductivity of a 1.5 M solution of an electrolyte is found
to be 138.9 Scm
-2
mol
-1
. Calculate the conductivity of this solution .
Ans : 0.20835

15. Example
Solution
The resistance of a 1 N solution of a salt is 50 . Calculate the
equivalent conductance of the solution, if the two platinum
electrodes in solution are 2.1 cm apart and each having an area of
4.2 cm
2
.
Ans : 10 ohm
−1
cm
2
eq
-1

16. Home Work

17. Example
Solution
Which of the following has higher molar conductivity.
(i)0.08 M solution and its specific conductivity is 2 × 10
-2

-1
cm
-1
(ii)0.1 M solution and its resistivity is 50  cm

18. Example
Solution
The reciprocal of electrical resistance is
(1)Voltage
(2)Current
(3)Conductance
(4)none of the above

19. Example
Solution
The resistance of a conductor varies inversely as
(1)length
(2)area of cross-section
(3)temperature
(4)resistivity

20. Example
Solution
The SI unit of specific resistance is
(1)ohm m
(2)ohm/m
(3)ohm/m
2
(4)(ohm)
-1