Variations of Conductivity with Concentration — Prelims Strategy

Prelims Strategy

To excel in NEET questions on 'Variations of Conductivity with Concentration', a multi-pronged strategy is crucial. Firstly, master the definitions and units of specific conductivity ($\kappa$) and molar conductivity ($\Lambda_m$), along with the conversion factor of 1000 when using concentration in mol L$^{-1}$ and $\kappa$ in S cm$^{-1}$.

Secondly, understand the qualitative trends: remember that $\kappa$ always decreases with dilution, while $\Lambda_m$ always increases with dilution. The key is to know why these trends occur and how they differ for strong and weak electrolytes.

For strong electrolytes, focus on reduced inter-ionic attractions and the linear $\Lambda_m$ vs. $\sqrt{c}$ plot (Debye-Hückel-Onsager equation). For weak electrolytes, emphasize the increased degree of dissociation and the sharp, non-linear $\Lambda_m$ vs.

$\sqrt{c}$ plot. Practice interpreting these graphs. Thirdly, practice numerical problems extensively. Be proficient in calculating $\Lambda_m$ from $\kappa$ and vice-versa. Also, practice problems involving the degree of dissociation ($\alpha = \Lambda_m / \Lambda_m^\circ$) for weak electrolytes.

Pay close attention to units and significant figures. Finally, be aware of common trap options, such as confusing the trends of $\kappa$ and $\Lambda_m$, or misapplying the Debye-Hückel-Onsager equation to weak electrolytes.