Specific Conductivity and Molar Conductivity - Definition, Unit, Relation, FAQs

Edited By Team Careers360 | Updated on Jul 02, 2025 04:55 PM IST

Here in this article we will be discussing about conductance, conductivity, symbol of conductance, what is specific conductance, definition of specific conductivity, unit of specific conductivity, Specific conductivity of a solution, ratio of specific conductance to that of conductance, definition and relationship between conductivity and molar conductivity, what is equivalent conductivity and everything related to specific and molar conductivity will be discussed here.

What is meant by Conductance?

The term conductance is the reciprocal of resistance and it is denoted by the symbol G. Conductance can be defined as the measure of ease of current flow through a conductor. It can be given by the formula:

Conductance, G=1/R ……………(1)

In equation (1), ‘R’ is the resistance of the conductor. The unit of conductance is ohm^-1 or Ω^-1 and its SI unit is Siemens or S.

The conductance of a material generally depends on the following factors:

The nature of the metal.
The number of valence electrons present per atom.
Temperature (conductance generally decreases with increase in temperature).

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Ionic conductance

The capacity of an ion to conduct electricity is commonly defined as ionic conductance. The value of ionic conductance of a metal ion is affected by the extent of its hydration in aqueous solutions.

In the state of infinite dilution, the ionization of the electrolyte will be complete and all forces of interaction between the ions will have ceased to exist. Under such a condition, all the ions that can possibly be derived from the electrolyte under consideration are free to carry current. The motion of ionic charge causes electrical conductivity. It is called ionic conductivity or ionic conductance. Equivalent conductance, molar conductance and specific conductance are different types of conductance.

Conductivity or Specific conductance

Define specific conductance

The term specific conductance, nowadays referred to as property of any conductor which is the capacity to conduct electricity.It can be represented by the symbol ‘K’. Specific conductance gives the measure of capacity of a material to conduct electricity.

Specific conductance formula or conductivity can be given as:

1640162995997

In equation (2), ρ is the specific resistance.

We know that 1640162997034

Here in equation’R’ indicates the resistance of a conductor of length ‘l’ and ‘a’ is the area of cross section in cm².

Then,

1640163003707

Here in equation(4) ’G’ is the conductance 1640163002160 . Obviously if, and , then equation becomes,

Thus the conductivity or specific conductance of an electrolyte solution represents the conductance with unit length and unit cross section. In other words, conductivity or specific conductance of an electrolyte solution represents the conductance of one centimeter cube of the solution kept between two ‘’ electrodes of unit area of cross section and placed unit distance apart.

The unit of specific conductance is microsiemens/cm

The conductivity or specific conductance of an electrolyte depends on the following factors.
Nature of electrolyte – Strong electrolytes have high conductance whereas the weak electrolytes have low conductance.
Concentration of the solution – Molar conductance varies with concentration of the electrolyte.
Temperature – The conductivity of an electrolyte increases with increase in temperature.

What does the term cell constant indicate?

The term cell constant is obtained by dividing the distance between the two electrodes in a conductivity cell by the cross-section of the electrode. It is commonly expressed in the unit and its SI unit is.

The expression for conductivity of an electrolyte solution is given as:

i.e., Conductivity Conductance Cell constant

The cell constant can also be denoted as. Then the expression for ‘K’ becomes:

1640162996398

Hence from equation It is clear that the cell constant is the ratio of specific conductance and conductance.

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Equivalent conductivity or Equivalent conductance

Equivalent conductivity of an electrolyte solution of a given concentration is explained as the conducting power of ions formed from one equivalent of electrolyte present in solution. It is generally denoted as.

Specific conductance or conductivity (K) of a solution is related to equivalent conductivity by the equation:

Here in equation ’K’ is expressed in and the concentration ‘c’ in. Then the unit of is .

If ‘N’ is the normality of the solution and ‘K’ is expressed in then,

Also, students can refer,

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Molar conductivity or Molar conductance

Molar conductivity or molar conductance of an electrolyte solution of a given concentration can be defined as the ratio of conductivity and the molar concentration. It is denoted as.

Specific conductance or conductivity (K) of a solution is related to molar conductivity by the equation:

In equation, when ‘K’ is expressed in and the concentration ‘c’ in, then the SI unit of will be.

If ‘M’ is the molarity of the solution and ‘K’ is expressed in then,

For an electrolyte solution, is related to as:

1640163002656

Relation between conductivity and molar conductivity

Λm=KC

C is the concentration

K is the conductivity

Λm is the molar conductivity

Also check-

NCERT Chemistry Notes:

Frequently Asked Questions (FAQs)

1. What are conductivity cells?

Various types of specially prepared cells that are used to calculate conductance. They are called conductivity cells. These cells are made of Pyrex glass and fitted with two platinum electrodes. These are welded to platinum wires fused into the bottom of two thin glass tubes containing some mercury for making contact to the circuit by means of copper wires. The glass tubes are fixed rigidly into an ebonite cover so that the distance between the electrodes remains constant.

2. What is the difference between conductivity and molar conductivity?

The term conductivity represents the measure of an electrolyte's ability to conduct electricity flowing through it whereas the molar conductivity gives the conductivity measured per unit molar concentration of an electrolyte solution.

It is essential to consider the concentration of an electrolyte solution while determining the molar conductivity.

3. How does the concept of ionic mobility relate to conductivity?

Ionic mobility is the velocity of an ion in an electric field of unit strength. It directly affects conductivity because ions with higher mobility can carry charge more efficiently through the solution. Factors that increase ionic mobility, such as smaller ion size or lower solution viscosity, generally increase conductivity.

4. How does the nature of the electrolyte affect specific and molar conductivity?

The nature of the electrolyte affects conductivity through factors like ion size, charge, and solvation. Strong electrolytes generally have higher conductivities than weak electrolytes at the same concentration due to complete dissociation. Ions with higher charges and smaller sizes typically contribute more to conductivity.

5. How does temperature affect specific and molar conductivity?

Generally, both specific and molar conductivity increase with temperature. This is because higher temperatures increase ion mobility by reducing solution viscosity and weakening ion-ion interactions, allowing for easier movement of ions through the solution.

6. What is the difference between strong and weak electrolytes in terms of their conductivity behavior?

Strong electrolytes completely dissociate in solution, resulting in a large number of ions and high conductivity. Their molar conductivity decreases slightly with concentration due to ion-ion interactions. Weak electrolytes partially dissociate, leading to fewer ions and lower conductivity. Their molar conductivity increases significantly with dilution as the degree of dissociation increases.

7. How does the concept of transference number relate to conductivity?

The transference number is the fraction of the total current carried by a particular ion in solution. It's related to conductivity because ions with higher mobility and concentration contribute more to the overall conductivity. The sum of all transference numbers in a solution equals one.

8. What is specific conductivity in electrochemistry?

Specific conductivity, also called conductivity, is the ability of a solution to conduct electricity. It's measured in siemens per centimeter (S/cm) and depends on the concentration of ions in the solution. The higher the concentration of ions, the greater the specific conductivity.

9. What is the unit of molar conductivity?

The unit of molar conductivity is siemens centimeter squared per mole (S·cm²/mol). This unit reflects that molar conductivity is the conductivity per unit concentration of electrolyte.

10. How are specific conductivity and molar conductivity related?

Molar conductivity (Λm) is related to specific conductivity (κ) by the equation: Λm = κ / c, where c is the molar concentration of the electrolyte. This relationship shows that molar conductivity is the specific conductivity normalized for concentration.

11. How does specific conductivity differ from molar conductivity?

Specific conductivity measures the overall conductance of a solution, while molar conductivity measures the conductance per mole of electrolyte. Specific conductivity increases with concentration, whereas molar conductivity typically decreases with increasing concentration due to ion-ion interactions.

12. Why does molar conductivity generally decrease with increasing concentration?

Molar conductivity decreases with increasing concentration due to increased ion-ion interactions. As the solution becomes more concentrated, ions are closer together, leading to stronger electrostatic attractions and reduced mobility, which lowers the overall conductivity per mole of electrolyte.

13. What is the Kohlrausch law of independent migration of ions?

Kohlrausch's law states that at infinite dilution, each ion contributes independently to the molar conductivity of an electrolyte. This means that the molar conductivity at infinite dilution is the sum of the individual ionic conductivities of the cation and anion.

14. What is the Ostwald dilution law, and how does it relate to the conductivity of weak electrolytes?

The Ostwald dilution law relates the degree of dissociation of a weak electrolyte to its concentration: Ka = α²c / (1-α), where Ka is the dissociation constant, α is the degree of dissociation, and c is the concentration. This law helps explain why the molar conductivity of weak electrolytes increases with dilution.

15. What is the Walden product, and what does it tell us about ion mobility?

The Walden product is the product of the limiting molar conductivity (Λ°m) and the viscosity (η) of the solvent. It's approximately constant for a given ion in different solvents: Λ°m · η ≈ constant. This relationship suggests that ion mobility is inversely proportional to solvent viscosity.

16. How does the concept of activity coefficient relate to conductivity measurements?

The activity coefficient accounts for non-ideal behavior in electrolyte solutions. As concentration increases, ion-ion interactions become more significant, and the effective concentration (activity) of ions deviates from the actual concentration. This affects conductivity measurements, especially at higher concentrations.

17. What is the Fuoss-Onsager equation, and how does it improve upon the Debye-Hückel-Onsager equation?

The Fuoss-Onsager equation is an extension of the Debye-Hückel-Onsager equation that accounts for short-range ion-ion interactions and the effect of ion size. It provides a more accurate description of how molar conductivity varies with concentration, especially for more concentrated solutions of strong electrolytes.

18. How does the concept of molar conductivity at infinite dilution relate to the transport number of ions?

The transport number (t) of an ion is the fraction of the total current carried by that ion. At infinite dilution, the transport number of an ion is directly proportional to its limiting ionic conductivity (λ°): t₊ = λ°₊ / (λ°₊ + λ°₋) for a cation, and t₋ = λ°₋ / (λ°₊ + λ°₋) for an anion. This relationship allows the calculation of transport numbers from limiting molar conductivities.

19. What is the Onsager limiting law, and how does it describe the concentration dependence of conductivity?

The Onsager limiting law is an extension of the Debye-Hückel theory that describes how the molar conductivity of a strong electrolyte varies with concentration at low concentrations. It's expressed as Λm = Λ°m - (A + BΛ°m)√c, where A and B are constants that depend on the properties of the solvent and temperature. This law accounts for both the electrophoretic effect and the relaxation effect in reducing molar conductivity as concentration increases.

20. What is meant by "infinite dilution" in the context of molar conductivity?

Infinite dilution refers to a hypothetical state where the solution is so dilute that ion-ion interactions are negligible. At infinite dilution, molar conductivity reaches its maximum value (Λ°m) because each ion can move independently without interference from other ions.

21. What is the significance of molar conductivity at infinite dilution (Λ°m)?

Molar conductivity at infinite dilution (Λ°m) represents the maximum conductivity an electrolyte can achieve when ion-ion interactions are negligible. It's important for comparing the intrinsic conducting abilities of different electrolytes and for calculating dissociation constants of weak electrolytes.

22. How can you determine the degree of dissociation of a weak electrolyte using conductivity measurements?

The degree of dissociation (α) can be determined by comparing the molar conductivity of the weak electrolyte (Λm) to its molar conductivity at infinite dilution (Λ°m): α = Λm / Λ°m. This ratio indicates the fraction of the electrolyte that has dissociated into ions.

23. What is the Debye-Hückel-Onsager equation, and how does it relate to molar conductivity?

The Debye-Hückel-Onsager equation describes how molar conductivity varies with concentration for strong electrolytes: Λm = Λ°m - (A + BΛ°m)√c, where A and B are constants, c is concentration, and Λ°m is the molar conductivity at infinite dilution. This equation accounts for the decrease in molar conductivity with increasing concentration due to ion-ion interactions.

24. How can conductivity measurements be used to determine the solubility product (Ksp) of a sparingly soluble salt?

The solubility product can be determined by measuring the conductivity of a saturated solution of the sparingly soluble salt. The specific conductivity is converted to molar conductivity, which is then used to calculate the concentration of ions in solution. From this, the Ksp can be calculated using the solubility product expression.

25. How does the presence of common ions affect the conductivity of a weak electrolyte solution?

The presence of common ions decreases the conductivity of a weak electrolyte solution. This is due to the common ion effect, which suppresses the dissociation of the weak electrolyte, resulting in fewer ions in solution and thus lower conductivity.

26. What is the relationship between equivalent conductivity and molar conductivity?

Equivalent conductivity (Λeq) is related to molar conductivity (Λm) by the number of equivalents per mole of electrolyte (ν): Λeq = Λm / ν. For a 1:1 electrolyte, equivalent conductivity and molar conductivity are numerically equal.

27. What is the Grotthuss mechanism, and how does it contribute to the conductivity of certain solutions?

The Grotthuss mechanism, also known as proton hopping, is a process by which protons (H⁺) move through water or other hydrogen-bonded networks. This mechanism contributes significantly to the unusually high conductivity of acids in aqueous solutions, as protons can move more quickly than other ions.

28. How can conductivity measurements be used to monitor the progress of a chemical reaction?

Conductivity measurements can monitor reaction progress when the reaction involves a change in the number or mobility of ions. For example, in a neutralization reaction between an acid and a base, the conductivity typically decreases as highly mobile H⁺ and OH⁻ ions are replaced by less mobile salt ions.

29. What is the Wien effect, and how does it relate to conductivity?

The Wien effect, also known as the second Wien effect, is the increase in conductivity of weak electrolytes under very high electric fields. This occurs because the strong electric field increases the dissociation of the weak electrolyte, producing more ions and thus higher conductivity.

30. How does the concept of limiting molar conductivity relate to ion mobility?

Limiting molar conductivity (Λ°m) is directly related to ion mobility. It represents the molar conductivity at infinite dilution, where ion-ion interactions are negligible. The limiting molar conductivity of an electrolyte is the sum of the individual ionic conductivities, which are proportional to the mobilities of the ions.

31. What is the Debye-Falkenhagen effect, and how does it influence conductivity?

The Debye-Falkenhagen effect is the increase in conductivity of strong electrolytes at high frequencies of applied electric field. This occurs because the alternating field disrupts the ion atmosphere around each ion, reducing ion-ion interactions and allowing for greater ion mobility and thus higher conductivity.

32. How does the hydration of ions affect their contribution to conductivity?

Ion hydration affects conductivity by influencing ion size and mobility. Highly hydrated ions are effectively larger and move more slowly through the solution, contributing less to conductivity. Conversely, less hydrated ions are smaller and more mobile, contributing more to conductivity.

33. How can conductivity measurements be used to determine the critical micelle concentration (CMC) of a surfactant?

The critical micelle concentration (CMC) can be determined by measuring the conductivity of a surfactant solution at various concentrations. Below the CMC, conductivity increases linearly with concentration. At the CMC, there's a sharp change in the slope of the conductivity vs. concentration plot, indicating micelle formation.

34. What is the Kohlrausch's law of independent migration of ions, and how is it used in conductivity calculations?

Kohlrausch's law states that at infinite dilution, each ion contributes independently to the molar conductivity of an electrolyte. It's expressed as Λ°m = ν₊λ₊ + ν₋λ₋, where ν₊ and ν₋ are the number of cations and anions per formula unit, and λ₊ and λ₋ are their respective limiting ionic conductivities. This law is used to calculate limiting molar conductivities of electrolytes from tabulated ionic conductivity values.

35. How does the concept of ionic strength relate to conductivity measurements?

Ionic strength is a measure of the total ion concentration in a solution, accounting for both concentration and charge of ions. It affects conductivity by influencing ion-ion interactions and the thickness of the ionic atmosphere around each ion. Generally, solutions with higher ionic strength have lower molar conductivities due to increased ion-ion interactions.

36. What is the Nernst-Einstein equation, and how does it relate conductivity to diffusion coefficients?

The Nernst-Einstein equation relates the limiting molar conductivity of an ion (λ°) to its diffusion coefficient (D): λ° = |z|F²D / RT, where |z| is the absolute charge of the ion, F is Faraday's constant, R is the gas constant, and T is temperature. This equation shows that ions with higher diffusion coefficients (more mobile) have higher conductivities.

37. How can conductivity measurements be used to determine the pKa of a weak acid?

The pKa of a weak acid can be determined by measuring the conductivity of the acid solution at various concentrations. By plotting the molar conductivity against the square root of concentration and extrapolating to infinite dilution, the limiting molar conductivity can be found. This value, along with the measured molar conductivity at a given concentration, can be used to calculate the degree of dissociation and thus the pKa.

38. What is the Bjerrum length, and how does it relate to conductivity in electrolyte solutions?

The Bjerrum length is the distance at which the electrostatic interaction between two ions is equal to the thermal energy (kT). It's an important parameter in electrolyte theory and affects conductivity by influencing ion-ion interactions. Ions separated by less than the Bjerrum length are more likely to form ion pairs, reducing the number of free ions and thus lowering conductivity.

39. How can conductivity measurements be used to determine the degree of hydrolysis of a salt?

The degree of hydrolysis of a salt can be determined by measuring the conductivity of its solution and comparing it to the conductivity expected if no hydrolysis occurred. The difference in conductivity is due to the additional ions produced by hydrolysis. By using the appropriate relationships between conductivity and ion concentration, the degree of hydrolysis can be calculated.

40. What is the Debye-Hückel-Onsager theory, and how does it explain the decrease in molar conductivity with increasing concentration?

The Debye-Hückel-Onsager theory explains the decrease in molar conductivity with increasing concentration for strong electrolytes. It accounts for two effects: (1) the electrophoretic effect, where the ion atmosphere moves in the opposite direction to the central ion, creating friction; and (2) the relaxation effect, where the ion atmosphere takes time to reform as the ion moves, creating an opposing electric field. These effects become more pronounced at higher concentrations, reducing ion mobility and thus molar conductivity.

41. How does the concept of activity coefficients relate to the measurement of conductivity in non-ideal solutions?

Activity coefficients account for non-ideal behavior in electrolyte solutions, where the effective concentration (activity) of ions differs from their actual concentration. In conductivity measurements, activity coefficients become important at higher concentrations, where ion-ion interactions are significant. The measured conductivity reflects the activity of the ions rather than their nominal concentration, and activity coefficients are used to relate the two.

42. What is the Kohlrausch regulator, and how is it used in conductivity measurements?

The Kohlrausch regulator is a mixture of potassium chloride and hydrochloric acid used to maintain a constant hydrogen ion concentration in conductivity measurements. It's particularly useful when measuring the conductivity of solutions containing weak acids or bases, as it helps to minimize changes in pH that could affect the conductivity readings.

43. How does the concept of ion pairing affect conductivity measurements, especially for multivalent ions?

Ion pairing occurs when oppositely charged ions associate in solution, effectively reducing the number of free ions available for conduction. This phenomenon is more pronounced for multivalent ions due to stronger electrostatic attractions. Ion pairing decreases the measured conductivity below