Molar Conductivity
Why does the molar conductivity of a strong electrolyte increase only slightly on dilution while that of a weak electrolyte rises sharply?
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Solution
Weak electrolytes dissociate more completely on dilution
Molar conductivity is the conductance of all ions produced by one mole of electrolyte, and its variation with concentration depends on how the number of free ions changes. A strong electrolyte is already almost fully ionised even at moderate concentrations, so on dilution only the weak interionic attractions decrease, producing a small, gradual rise in molar conductivity described by the Debye-Hückel-Onsager equation. A weak electrolyte, however, is only partially dissociated; as it is diluted the degree of dissociation increases markedly, releasing many more ions and causing molar conductivity to climb steeply toward the limiting value at infinite dilution. Option claiming strong electrolytes ionise more on dilution is wrong because they are already near-complete ionisation. The option stating both behave identically contradicts experimental conductivity curves. The option that dilution removes ions misstates the physical effect, since dilution lowers concentration but increases ionisation for weak electrolytes. This distinction underpins Kohlrausch's law in NCERT. It is worth emphasising that this is not a special case but a representative example of how molar conductivity operates throughout redox reactions and electrochemistry. Plausibility check: a weak acid like acetic acid shows a dramatic conductivity rise on dilution, confirming the chosen answer.
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About This Question
- Subject
- chemistry
- Chapter
- redox reactions and electrochemistry
- Topic
- molar conductivity
- Difficulty
- Medium
- Year
- 2025
Solution
Correct Answer:
Weak electrolytes dissociate more completely on dilution
Molar conductivity is the conductance of all ions produced by one mole of electrolyte, and its variation with concentration depends on how the number of free ions changes. A strong electrolyte is already almost fully ionised even at moderate concentrations, so on dilution only the weak interionic attractions decrease, producing a small, gradual rise in molar conductivity described by the Debye-Hückel-Onsager equation. A weak electrolyte, however, is only partially dissociated; as it is diluted the degree of dissociation increases markedly, releasing many more ions and causing molar conductivity to climb steeply toward the limiting value at infinite dilution. Option claiming strong electrolytes ionise more on dilution is wrong because they are already near-complete ionisation. The option stating both behave identically contradicts experimental conductivity curves. The option that dilution removes ions misstates the physical effect, since dilution lowers concentration but increases ionisation for weak electrolytes. This distinction underpins Kohlrausch's law in NCERT. It is worth emphasising that this is not a special case but a representative example of how molar conductivity operates throughout redox reactions and electrochemistry. Plausibility check: a weak acid like acetic acid shows a dramatic conductivity rise on dilution, confirming the chosen answer.
This medium difficulty chemistry question is from the chapter redox reactions and electrochemistry, covering the topic of molar conductivity. It appeared in the 2025 exam.
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