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Electrochemistry question

2019 · 10 Apr · Shift 1 · Q19
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Electrochemistry question

2019 · 10 Apr · Shift 1 · Q19

JEE MainChemistryElectrochemistryMCQ+4 / −1
Consider the statements S1 and S2 S1 : Conductivity always increases with decrease in the concentration of electrolyte. S2 : Molar conductivity always increases with decrease in the concentration of electrolyte. The correct option among the following is :
  1. A
    Both S1 and S2 are wrong
  2. B
    S1 is correct and S2 is wrong
  3. C
    Both S1 and S2 are correct
  4. D
    S1 is wrong and S2 is correct
View written solutionFree

Correct answer: D

  1. Understand the two quantities

    • Conductivity (κ)(\kappa)(κ): conductance of a solution contained between electrodes of unit area and unit distance apart.
    • Molar conductivity (Λm)(\Lambda_m)(Λm​): conductivity due to all ions produced by 1 mole of electrolyte.

    They are related by Λm=κ×1000C\Lambda_m = \frac{\kappa \times 1000}{C}Λm​=Cκ×1000​ where CCC is concentration in mol L−1\text{mol L}^{-1}mol L−1.

  2. Check Statement S1: Conductivity always increases with decrease in concentration of electrolyte.

    This is false.

    Reason: On dilution, the number of ions per unit volume decreases, so conductivity κ\kappaκ generally decreases.

    Thus, conductivity does not always increase when concentration decreases.

  3. Check Statement S2: Molar conductivity always increases with decrease in concentration of electrolyte.

    This is true.

    Reason: On dilution, ions move more freely because interionic interactions decrease. Therefore, molar conductivity increases.

    • For strong electrolytes, it increases slowly with dilution.
    • For weak electrolytes, it increases sharply because ionization also increases.

    Hence, Λm\Lambda_mΛm​ increases with decrease in concentration.

  4. Conclusion

    • S1S1S1 is wrong
    • S2S2S2 is correct

    Therefore, the correct option is: D\boxed{D}D​

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