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Home > News & Articles > Molar Conductivity: Definition, Formula, Importance, Variation, Application & Solved Examples
Updated on 27th April, 2023 , 6 min read
Molar conductivity is a fundamental concept in chemistry that describes the ability of a solution to conduct electric current. It is a critical parameter used to understand the behaviour of electrolytes in solution and is widely used in various chemical and electrochemical applications. In this article, we will delve into the definition, importance, and applications of molar conductivity, providing a comprehensive understanding of this key concept in chemistry.
Molar conductivity, denoted by the symbol λ (lambda), is defined as the conductance of a solution containing one mole of solute dissolved in a given volume of solvent, typically one liter. It is expressed in units of Siemens per meter (S/m) or Siemens per centimeter (S/cm). Molar conductivity is a measure of the ability of ions to migrate through a solution under the influence of an electric field.
Molar conductivity can be determined experimentally by measuring the conductance of a solution using a conductivity meter and dividing it by the concentration of the solute in moles per liter (mol/L) or millimoles per liter (mmol/L). Mathematically, it is given by the equation:
λ = κ / c
Where λ is the molar conductivity, κ is the conductance of the solution in S/cm (or S/m), and c is the concentration of the solute in mol/L (or mmol/L).
The following expression is used to mathematically represent molar conductivity.
Λm = K / C
Where K is the specific conductivity and c is the concentration in mole per litre.
In general, the molar conductivity of an electrolytic solution is the conductance of the volume of the solution containing a unit mole of electrolyte that is placed between two electrodes of unit area cross-section or at a distance of one centimeter apart.
The unit of molar conductivity is S⋅m2⋅mol-1.
Molar conductivity is a crucial parameter in understanding the behaviour of electrolytes in solution. Electrolytes are substances that dissociate into ions when dissolved in a solvent, and their ability to conduct electricity is directly related to the concentration and mobility of these ions in solution. Molar conductivity provides valuable information about the extent of dissociation of electrolytes and the mobility of ions, which is vital in various chemical and electrochemical processes.
Some of the key reasons why molar conductivity is important are:
Molar conductivity finds applications in various fields of chemistry and electrochemistry. Some of the notable applications are:
When weak and strong electrolytes are diluted, their molar conductivity increases. Molar conductivity refers to the conductivity provided by one mole of ions. Even after dilution, the solution still contains the same quantity of one mole of ions. However, increased dilution causes more electrolytes to dissociate into ions, effectively increasing the number of active ions in the solution. The greater number of active ions in the solution imparts greater conductivity.
IMAGE
The provided graph illustrates that the molar conductivity of strong electrolytes increases gradually with dilution. Kohlrausch's law can be used to express the general equation for the plot of strong electrolytes, where slope A depends on the electrolyte type and the temperature and solvent used. The molar conductivity of weak electrolytes, on the other hand, increases rapidly at lower concentrations but decreases at higher concentrations due to reduced dissociation.
Regarding specific conductivity, the conductivity increases as the concentration of the electrolyte increases. This is because the current-carrying ions increase in solution with increasing dissociation due to dilution. However, the number of ions per unit volume of the solution decreases with dilution, causing a reduction in conductivity. Strong electrolytes exhibit a sharp increase in conductivity with increasing concentration. Conversely, weak electrolytes have low specific conductivity at lower concentrations, and the value increases gradually with concentration due to the increase in active ions in the solution.
Given:
Molarity (M) = 0.30M
Conductivity at 298 K (k) = 0.023 S cm–
Solution:
Molar conductivity = (1000 × k) /M
= (1000 × 0.023) / 0.30
= 76.66 cm² mol⁻¹
Therefore, the molar conductivity of the KCl solution is 76.66 cm² mol⁻¹.
Given:
Molarity (M) = 0.20M
Conductivity at 298 K (k) = 0.0248 S cm–
Solution:
Molar conductivity = (1000 × k) /M
= (1000 × 0.0248) / 0.20
= 124 cm² mol⁻¹
Therefore, the molar conductivity of the KCl solution is 124 cm² mol⁻¹.
Solution:
Molar conductance at infinite dilution
λ+Na = 51.12×10−4 Sm2mol−1
λ+Cl = 73.54×10−4 Sm2mol−1
Molar conductance of NaCl = λ+Na + λ+Cl
= 51.12×10−4 + 73.54×10−4
= 124.66 ×10−4 Sm2mol−1
Therefore, the molar conductance of NaCl is 124.66 ×10−4 Sm2 mol−1.
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By - Nikita Parmar 2023-08-25 09:48:44 , 11 min readMolar conductivity is the ability of a solution to conduct electricity and is defined as the conductivity of a solution containing one mole of solute per liter of solution.
The unit of molar conductivity is Siemens per meter squared per mole (S m²/mol).
For strong electrolytes, molar conductivity decreases with increasing concentration due to increased ion-ion interactions, while for weak electrolytes, molar conductivity increases with increasing concentration due to increased dissociation.
Kohlrausch’s law states that the limiting molar conductivity of an electrolyte is the sum of the molar conductivity of its cations and anions at infinite dilution.
The molar conductivity of an electrolyte is proportional to the degree of dissociation, which is the fraction of the total amount of electrolyte that has dissociated into ions.
The limiting molar conductivity provides information on the strength of an electrolyte and the ease with which it dissociates into ions in a solution.
As temperature increases, the molar conductivity of a solution generally increases due to increased mobility of ions, although some exceptions exist.
The degree of dissociation of an electrolyte can be determined by measuring its molar conductivity at different concentrations and extrapolating to infinite dilution using Kohlrausch’s law.
The molar mass of an electrolyte can be determined by measuring its molar conductivity and using the relationship between molar conductivity and molar mass.
Molar conductivity can provide information about the strength and behavior of an electrolyte, but it cannot be used alone to determine the identity of an unknown compound. Other analytical techniques are typically required to identify unknown compounds.
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