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Electrochemistry — Chemistry STD 12 Science — Question

Maharashtra BoardEnglish MediumSTD 12 ScienceChemistryElectrochemistry3 Marks
Question
Explain the variation of molar conductivity with concentration for strong and weak electrolytes.
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How is the molar conductivity of strong electrolytes at zero concentration determined by graphical method? Why is this method not useful for weak electrolytes?
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Answer

(i) As the dilution of an electrolytic solution increases, the dissociation of the electrolyte increases, hence the total number of ions increases, therefore, the molar conductivity increases.
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(ii) The increase in molar conductivity with increase in dilution or decrease in concentration is different for strong and weak electrolytes.
(iii) On dilution, the molar conductivity of strong electrolytes increases rapidly and approaches to a maximum limiting value at infinite dilution or zero concentration and represented as $\wedge \infty$ or $\wedge_0$ or $ \wedge^0{ }_m $. In case of weak. In case of weak electrolytes which dissociate less as compared to strong electrolytes, the molar conductivity is low and increases slowly in high concentration region, but increases rapidly at low concentration or high dilution. This is because the extent of dissociation increases with dilution rapidly.
(v) $\wedge_0$ values for strong electrolytes can be obtained by extrapolating the linear graph to zero concentration (or infinite dilution). However $\wedge_0$ for the weak electrolytes cannot be obtained by this method, since the graph increases exponentially at very high dilution and does not intersect $\wedge_{ m }$ axis at zero concentration.

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