Engineering Chemistry S Datta

226 ENGINEERING CHEMISTRY
Q. 15. What is specific conductance?
Ans. The specific conductance (K) is the reciprocal of specific resistance (ρ).
K = 1 ρ =
1
R
F l
H G I K J
a
It is defined as the conductance of 1 cm 3 of a conductor
unit of K = ohm –1 cm –1
Q. 16. What do you mean by equivalent conductivity of an electrolytic solution?
Ans. It is the conducting power of all the ions present in a solution of an electrolyte
containing 1 g equiv.
Equivalent conductivity λ eq
= 1000 K
C
C = normality of the solution.
Unit of λ eq
= ohm –1 cm 2 equiv –1 .
Q. 17. What do you mean by molar conductivity of an electrolyte?
Ans. It is the conductivity of all the ions produced in a solution containing one gm mole
of the electrolyte. i.e., molar conductivity λ m
= 1000 K
M
where, M = molarity of the solution
K = specific conductance.
Q. 18. Give the relationship of molar conductivity with concentration.
Ans. The relation is
λ m
= λ
∞
m
– b c
where, b = constant c = concentration
λ
∞
m
= molar conductivity at infinite dilution
λ m
= molar conductivity at a given dilution
As c → 0 λ m
= λ ∞ m
.
Q. 19. What is the effect of dilution on molar conductivity?
Ans. Molar conductivity increases with dilution.
Q. 20. What do you mean by degree of dissociation of an electrolyte?
Ans. The degree of dissociation (α) is the fraction of the electrolyte that dissociates into
ions. For weak electrolytes it is related to λ m
and λ
∞
m
as follows:
α = λ m
∞
λ
.
m
Q. 21. What is transport number?
Ans. It is the fraction of total quantity of electricity, carried by cations or anions.
Q. 22. Define Kohlrausch’s law.
Ans. The molar conductance, at infinite dilution of an electrolyte, is equal to the sum of
ionic conductances of cations and anions.
Q. 23. What are the applications of conductance measurement?
Ans. (i) Measurement of degree of dissociation.
(ii) Determination of solubility and solubility product.
(iii) Conductometric titration.