1. Chapter 2 - Electrolyte conductance
Lecture no.2

2. Molar Conductivity Behaviour of Strong and Weak Electrolytes
Most compounds that dissolve in water and undergo ionization behave differently in highly dilute solutions compared to concentrated solutions.
Molar conductivity (Λ) of electrolytes increases with dilution.
The variation is different for strong and weak electrolytes.

3. 1. Molar Conductivity Behaviour of Strong Electrolyte
Compounds that exhibit molar conductivities that do not change significantly with concentration are referred to as strong electrolytes.

4. Λ = Λº - β√C
DEBYE HUCKEL ONSAGER equation.

5. As conclusion…Conductance behaviour of strong electrolyte:
No increase in the no. of the ions with the dilution ( completely ionized in the solution at all concentration).
In concentrated solution:
- strong inter-ionic forces
- Molar conductivity is low
In dilute solution:
- Inter-ionic forces low
- Molar conductivity increases with dilution
When concentration very low, inter-ionic interaction becomes almost negligible and molar conductance approaches the limiting value, Λ°.

7. 2. Molar Conductivity Behaviour of Weak Electrolyte
For weak electrolyte i.e. acetic acid, the increase in dilution shows significant increase in molar conductivity.
WHY???
Weak electrolytes are nearly completely ionize at low concentrations but are incompletely ionized at higher concentrations.
THUS
Their dissociation is strongly concentration dependent.

8. As conclusion… Conductance behaviour of weak electrolyte:
The no. of ions produced in solution depends upon the degree of dissociation with dilution.
The higher the degree of dissociation, the larger is the molar conductance.
With increase in dilution:
- Degree of dissociation increases as a result molar conductivity increases.
- At infinite dilution, the electrolyte is completely dissociated so that the degree of dissociation, α become one.
Thus, if Λ = molar conductivity at a given concentration and, Λ° = limiting molar conductivity, therefore:
α = Λ /Λº

9. Degree of Dissociation, α
The degree of dissociation (α) of the electrolyte on its molar conductivity by the Arrhenius expression:
Arrhenius assumed: incomplete dissociation at higher concentration but complete dissociation at infinite dilution.

10. Exercise…
Molar conductivity for 0.10 M NaCl is 107 S.cm2 mol-1. Calculate the degree of dissociation,α for the solution.

11. KOHLRAUSCH’S LAW 
At infinite dilution the ions act completely independently, and the Λ° obeys a rule of additivity:
where AX, AY, BX and BY are strong electrolytes.

12. Λ° for a weak electrolyte can be deduced from ° values obtained from strong electrolytes.
For example, consider CH3COOH:
Λ° CH3COOH = Λ° (HCl) + Λ° (KHCOO3) - Λ°(KCl)
Exercise:
Find the Λ° for NH4OH.

13. Kohlrausch also stated at infinite dilution when the dissociation complete, each ion makes a definite contribution towards molar conductance of the electrolyte irrespective of the nature of the other ion with which it is associated.
It means that the molar conductivity at infinite dilution for a given salt can be expressed as the sum of the individual contributions from the ions of the electrolyte.