Equivalent Conductance

The conductance of a volume of solution containing one equivalent of an electrolyte is known as equivalent conductance. The symbol for equivalent conductance is Λ.

Consider the volume of solution Vcm³ having one equivalent of an electrolyte. It has the same conductance as equivalent conductance, Λ.

We also know that specific conductance, κ refers to the conductance indicated by a 1 cm³ solution containing this electrolyte.

i.e.,

 conductance of Vcm³ ——— Λ

conductance of 1 cm³———κ

Therefore,

=κ×V ………. equation (1)

The Normality(N) of a solution can be given as:

N=ne/V (in cc)×1000 ………equation (2)

In the above equation, number of equivalents, ne=1

When we put the value of ne in equation (2) we get,

V (in cc)=1000/N 

Now when we put the value of V in equation (1) we get,

=κ×1000/N 

Equivalent conductance unit

The unit of equivalent conductance is ohm-¹cm²/gram

OR  siemens m²/gram

Molar conductance

Molar conductance is the conductance of a volume of solution containing one mole of an electrolyte.

It is denoted by the symbol Λ mor μ.

Molar conductance is related to specific conductance, as:

μ = κ.V 

OR

μ = κ.1000/M 

In the above relation,

M is the molarity of the solution

Molar conductance unit 

The unit of molar conductivity is cm2  . ohm-¹ . mol-¹

OR m². Siemens. mol -¹.

The relationship between equivalent conductance, and molar conductivity, Λ m can be expressed as:

Λ m= ×(equivalent factor of the electrolyte) 

Specific Conductance

The conductance of an electrolytic solution enclosed between two electrodes 1 cm apart and 1 cm²area is called specific conductance (L). To put it another way, the specific conductance (L) can be defined as the conductance of a 1 cc solution enclosed between two electrodes separated by 1 cm. 

The unit of specific conductance (L) is ohm-¹ cm-¹ OR  siemens m-¹

The number of ions present per cc of solution, the charge of the ions, and the speed of the ions all influence specific conductance (L). It is also affected by the temperature of the electrolytic solution, increasing by 2% for every degree that the temperature rises. As a result, as the strong electrolyte solution is diluted, the quantity of ions per cc declines while ion speed increases. However, the first element takes precedence over the second, and L decreases when the solution is diluted.

Kohlrausch Law

The total number of ions fixed in 1 gramme equivalent electrolyte solution is always set since the strong electrolyte solution is fully dissociated at any concentration. As a result of less interionic interaction among the ions, the speed of the ions increases with dilution. The interionic attraction forces dissipate at a certain dilution, and riches limiting values disappear. For a strong electrolyte solution that obeys the Kohlrausch law of independent migration, it is called equivalent conductance at infinite dilution (Λ0).

Application of Conductivity Measurement 

• The ability of an electrolyte solution to conduct electricity is direct evidence of the presence of ions in the solution. The behaviour of ions in a solution can be determined experimentally by measuring conductance.
• Electrical conductance measurements are used to determine physical quantities such as the endpoint of an acid-base titration, the solubility of sparingly soluble salts, the ionic product of water, and the chemical kinetics of processes.
• In the agricultural industry, measuring the electrical conductivity of soil is essential for crop health and growth. It’s used to keep track of important soil nutrients like phosphorus, nitrates, calcium, and potassium, all of which are important for plant growth.
• Conductance is a quick and easy approach to determine the solubility of a salt that is sparingly soluble, such as silver chloride (AgCl).

Factors Affecting Equivalent Conductance

• Temperature: The conductance of an electrolyte solution increases as the extent of ionisation increases with rising temperature.
• Strong electrolytes undergo complete ionisation, resulting in higher conductivities due to the higher number of ions produced.
• Weak electrolytes, on the other hand, are partially ionised and so have low conductivities in their solutions.
• Ionic size and mobility: As an ion’s size increases, its mobility decreases, and its conductivity decreases.
• Due to the general nature of the solvent and its viscosity, ionic mobility is reduced in more viscous solvents. The conductivity decreases as a result.
• With an increase in solution concentration, the specific conductance rises as the number of ions per unit volume rises.
• The equivalent conductivity and molar conductance, on the other hand, rise when the amount of ionisation decreases with decreasing concentration (i.e., dilution).

Conclusion

The equivalent conductance of an electrolyte is defined as the conductance of a volume of solution containing one equivalent weight of dissolved substance when placed between two parallel electrodes 1 cm apart and large enough to accommodate the entire solution. Λ is estimated from a specific conductance rather than being determined directly. If C is the concentration per cubic centimetre, then 1000/C is the volume that contains one equivalent of the solute. As Ls, is the conductance of a centimetre cube of the solution, the conductance of 1000/C cc, will be

Λ=1000Ls/C