Limiting molar conductivity of an electrolyte cannot be determined experimentally why

Solution : In weak electrolyte the conductivity of the solution increases very slowly with dilution of solution and goes on increasing upto infinity. Hence, it can not be measured experimentally. <br> <img src="https://doubtnut-static.s.llnwi.net/static/physics_images/OSW_GRU_SQP_XII_T2_SS_PCB_CHE_SP_01_E01_026_S01.png" width="80%">

Solution : We can determine the molar conductivity of an electrolytic solution at infinite dilution `(Delta_(m)^(@))` , if the plot of molar conductivity vs concentration (obtained from experiments ) is extrapolated to zero concentration is extrapolated to zero concentration. As `Delta_(m)` of the solution of a strong electrolyte varies linearly with the concentrations of the solution , the method of extrapolation is used to determine `Delta_(m)^(@)` for strong electrolytes . However , this method cannot be use for the solution of a weak eletrolyte because `Delta_(m)` for such a solution keeps on increasing with dilution even at very low extrapolation becomes invalid . Hence , molar conductivity of a weak electrolyte at infinite dilution cannt be determined experimentally .

If both assertion and reason are true, and reason is the true explanation of the assertionif both assertion and reason are true, but reason is not the true explanation of the assertion.if assertion is true, but reason is false.If both assertion and reason are false.

Answer : B

Solution : Correct explanation. The dissociation of weak electrolyte keeps increasing with dilution and is not complete even infinite dilution.

Answer

Verified

Hint: We must know that the conducting power of all the ions made by dissolving one mole of an electrolyte in a solution is called molar conductivity. Kohlraush’s law can be defined as the equivalent conductivity of an electrolyte at infinite dilute is equal to total conductance of the anions and cations.

Complete step by step answer:
We know that molar conductivity of a solution comprises one mole of the electrolyte and it is not constant. It is the conductance unit mole of electrolyte, which is placed between two electrodes of unit cross section or at a separate distance of one-centimeter.
Kohlraush’s law can be defined as the equivalent conductivity of an electrolyte at infinite dilute is equal to total conductance of the anions and cations.
We explain the assertion as molar conductivity of a strong electrolyte at infinite dilution could be calculated by extrapolation as linear plot is obtained. In the case of weak electrolyte, the molar conductivity at infinite solution cannot be measured experimentally and by extrapolation because the plot obtained is not linear, the highest value of molar conductivity at infinite solution cannot be determined.
The dissociation of weak electrolyte keeps rising with dilution and is not finished even with infinite dilution.
The assertion and reason is true but reason is not the correct explanation for assertion.
Hence, option (B) is correct.

Note:
Kohlraush’s law helps in determining the limiting molar conductivity of any electrolytes. Weak electrolytes contain lower molar conductivities and lower degree of dissociation for higher concentration. It is used to calculate the dissolution of salts that are sparingly soluble.

asked Jan 9, 2019 in Electrochemistry by (78.0k points)
recategorized Feb 12, 2020 by subrita

Assertion : Molar conductivity of a weak electrolyte at infinite dilution cannot be determined experimentally.

Reason : Kohlrausch law helps to find the molar conductivity of a weak electrolyte at infinite dilution.

(a) Both A and R are true and R is the correct explanation of A

(b) Both A and R are true but R is not correct explanation of A

(c) A is true but R is false

(d) A and R are false

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