The electrical transport property of a material is defined by its resistance and conductivity. Resistance is the measure of a material's ability to resist the flow of electric current, while conductivity gauges its ability to allow the current to pass through, depending on the geometry of the measurement cell, such as electrode spacing and area. Conductivity is measured in Siemens (S). There are different types of conductance, including specific conductance, equivalent conductance, and molar conductance.
Specific conductance removes geometric effects and refers to the conductance of a material with a length of 1 meter and a cross-sectional area of 1 square meter; it's measured in Siemens per meter (S/m). Generally, specific conductivity is determined with the cell constant- the ratio of the distance between the electrodes to the area of the cross-section of the electrodes.
Equivalent conductance focuses on ion quantity rather than volume alone. It is defined as the conductance of ions produced by one gram equivalent of an electrolyte. Numerically, it is the product of the specific conductance and the volume, in cubic meters, that contains one gram equivalent of the electrolyte. This is expressed in Siemens per square meter (S m2).
Molar conductivity, on the other hand, refers to the conductance of ions produced by one mole of an electrolyte. It's calculated by dividing the specific conductance by the number of moles of electrolytes per cubic meter of solution. The unit of molar conductivity is Siemens square meter per mole (S m2 /mol ). Molar conductance is especially useful because it reveals how ion mobility and electrolyte dissociation vary with concentration, making it important to examine its behavior in both concentrated and dilute solutions.
In strong electrolytes, the plot of molar conductivity against dilution shows that molar conductivity tends to approach a limiting value as concentration approaches zero. The molar conductivity at this point is referred to as molar conductivity at zero concentration or molar conductivity at infinite dilution. As the dilution increases, so does the molar conductivity of an electrolyte due to an increase in the degree of dissociation of electrolytes. However, the rise in the number of ions during dilution is significantly less than the increase in the volume of the solution. It follows that specific conductivity decreases with increasing dilution.
Conductance G is the inverse of resistance R. It shows how easily electricity flows through a solution, depending on the geometry of the measurement cell.
To remove the effect of cell geometry, conductance is multiplied by the cell constant Kcell, defined as the distance between electrodes divided by their cross-sectional area. This gives the specific conductance, κ, which represents the conductance of a one-meter cube of the solution.
Equivalent conductance Λ relates conductance to the amount of electrolyte. It represents the conductance of ions produced by one gram equivalent of an electrolyte and equals κ multiplied by the volume containing one gram equivalent.
Meanwhile, molar conductance Λm describes the conductance due to ions from one mole of electrolyte and is obtained by dividing κ by the molar concentration of the added electrolyte.
As an electrolyte's dilution increases, its Λm increases due to greater electrolyte dissociation, while κ decreases since the total number of ions per unit volume drops.
As the concentration approaches zero, the Λm of strong electrolytes reaches a limiting value, called the molar conductance at infinite dilution, Λ°m.
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