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.