Practicing Success
Conductivity of electrolytes is measured by using conductivity cell which contains two electrodes separated by a fixed distance \(‘l’\) and have an area of cross-section \(A\) The resistance R of conductivity cell is given by the relation \[R = \frac{\rho l}{A} = \frac{l}{\kappa A}\] The quantity \(l/A\) for a particular conductivity cell is constant denoted by \(G^*\) and is called cell constant. The cell constant can be determined by using a \(KCl\) solution whose conductivity is known accurately at various concentrations. The cell constant \(G^* = l / A = R\kappa\). The conductances of different solutions can be determine by using Wheatstone bridge principle. The specific conductance of a solution k is given by \[\kappa =\frac{G}{R}\] The total conductance of the solution is the product of specific conductance and volume of the solution \(\kappa × V\). If the amount of electrolyte dissolved in solution is equal to the gram equivalent weight of the electrolyte, then the total conductance is known as equivalent conductance \[\Lambda eq = 1000K /C\], where C is the concentration of solution in gram equivalents per litre. The unit of equivalent conductivity is \(\Omega^{−1}cm^2 eq^{−1}\) or \(Scm^2eq^{−1}\). If the amount of electrolyte dissolved in solution is equal to the gram molecular weight of electrolyte, then the total conductance is known as molar conductivity \((\Lambda_M)\). The unit of molar conductivity is \(\Omega^{−1}cm^2 mol^{−1}\). According to SI system, molar conductance is expressed as \(S m^2 mol^{−1}\), if concentration is expressed in \(mol\text{ }m^3\). Specific conductance always decreases with the decrease in concentration both for strong and weak electrolytes due to the decrease in the number of ions per unit volume that carry the current in a solution. |
Which of the following statement is not correct? |
When the solution of weak electrolyte is diluted, specific conductivity decreases When the solution of weak electrolyte is diluted, molar conductivity increases Equivalent conductance of a weak electrolyte solution on dilution increases. Dilution of a weak electrolyte solution does not affect the either equivalent conductance or molar conductance |
Dilution of a weak electrolyte solution does not affect the either equivalent conductance or molar conductance |
The correct answer is: (4) Dilution of a weak electrolyte solution does not affect either the equivalent conductance or molar conductance. |