Question

Write the difference between molar conductance and specific conductance.

Answer 1

The conductivity of an electrolyte when divided by molar concentration is called molar conductance whereas the ability of an electrolyte to conduct electricity in meters is known as specific conductance.

Complete step-by-step answer:
We denote molar conductance by $\lambda$ and molarity of an electrolyte as M. Then the molar conductance of an electrolyte which is dissolved in one mole of its solution can be calculate of the formula: $\lambda = \dfrac{k}{M}$ , where k is the specific conductance.
We introduced this concept of molar conductance because the electrolytic conductivity is not suitable for comparing the conductance of different solutions at different concentrations. Molar conductance varies according to the nature of the electrolyte. It increases when the electrolyte is diluted as a greater number of moles dissociate. Therefore, the weak electrolytes have less molar conductance.
We can also write molar conductance as $\lambda = k \times V$ where k is the specific conductance and V is the diluted volume of the solution. Its units will be $oh{m^{ - 1}}c{m^2}mo{l^{ - 1}}$ or $Sc{m^2}mo{l^{ - 1}}$.
The specific conductance(k) is measured as per the length and area covered by an electrolyte. It is inversely proportional to specific resistance and is given by Siemens/meter or G/m. We know that specific resistivity is $\rho = \dfrac{{RA}}{l}$ from $R = \rho \dfrac{l}{A}$. The reciprocal of specific resistance is called as specific conductance denoted as kappa (k). Then,
$\rho = \dfrac{1}{k}$ from $R = \dfrac{1}{G}$.
We know that the characteristic constant of the cell is cell constant (l/A). Therefore, specific conductance is a product of conductance and cell constant. Its units are $Sc{m^{ - 1}}$ or $oh{m^{ - 1}}c{m^{ - 1}}$.

Note: Molar conductance can also be called as ionic strength of a solution as it is the conducting power of all the ions which are produced by dissolving one mole of an electrolyte in the solution. We can also represent it in terms of specific conductance as $\lambda = k \times \dfrac{{1000}}{M}$