Conductance And Kohlrausch's Law
Using Kohlrausch's law, the limiting molar conductivity of CH₃COOH can be obtained from the limiting molar conductivities of which set of electrolytes?
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Solution
CH₃COONa, HCl, and NaCl
Kohlrausch's law of independent migration of ions states that Λ°(CH₃COOH) = λ°(CH₃COO⁻) + λ°(H⁺). We can obtain these ionic conductivities by combining strong electrolytes: Λ°(CH₃COONa) = λ°(CH₃COO⁻) + λ°(Na⁺), Λ°(HCl) = λ°(H⁺) + λ°(Cl⁻), and Λ°(NaCl) = λ°(Na⁺) + λ°(Cl⁻). Therefore: Λ°(CH₃COOH) = Λ°(CH₃COONa) + Λ°(HCl) − Λ°(NaCl). This algebraic combination cancels out Na⁺ and Cl⁻ contributions, leaving only CH₃COO⁻ and H⁺. This is the classic application of Kohlrausch's law to determine limiting molar conductivity of weak electrolytes that cannot be measured directly due to incomplete dissociation even at high dilution.
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About This Question
- Subject
- chemistry
- Chapter
- redox reactions and electrochemistry
- Topic
- conductance and kohlrausch's law
- Difficulty
- Medium
- Year
- 2025
Solution
Correct Answer:
CH₃COONa, HCl, and NaCl
Kohlrausch's law of independent migration of ions states that Λ°(CH₃COOH) = λ°(CH₃COO⁻) + λ°(H⁺). We can obtain these ionic conductivities by combining strong electrolytes: Λ°(CH₃COONa) = λ°(CH₃COO⁻) + λ°(Na⁺), Λ°(HCl) = λ°(H⁺) + λ°(Cl⁻), and Λ°(NaCl) = λ°(Na⁺) + λ°(Cl⁻). Therefore: Λ°(CH₃COOH) = Λ°(CH₃COONa) + Λ°(HCl) − Λ°(NaCl). This algebraic combination cancels out Na⁺ and Cl⁻ contributions, leaving only CH₃COO⁻ and H⁺. This is the classic application of Kohlrausch's law to determine limiting molar conductivity of weak electrolytes that cannot be measured directly due to incomplete dissociation even at high dilution.
This medium difficulty chemistry question is from the chapter redox reactions and electrochemistry, covering the topic of conductance and kohlrausch's law. It appeared in the 2025 exam.
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