Following figure shows dependence of molar conductance of two electrolytes on concentration. is the limiting molar conductance.
The number of incorrect statement(s) from the following is ______
(A) for electrolyte A is obtained by extrapolation
(B) For electrolyte B, vs graph is a straight line with intercept equal to
(C) At infinite dilution, the value of degree of dissociation approaches zero for electrolyte B.
(D) for any electrolyte A or B can be calculated using for individual ions
The number of incorrect statement(s) from the following is ______
(A) for electrolyte A is obtained by extrapolation
(B) For electrolyte B, vs graph is a straight line with intercept equal to
(C) At infinite dilution, the value of degree of dissociation approaches zero for electrolyte B.
(D) for any electrolyte A or B can be calculated using for individual ions
Show answer and solution
Answer: 2
Solution
From the graph, electrolyte A is a weak electrolyte (curve that doesn't extrapolate linearly) and electrolyte B is a strong electrolyte (linear Λm vs √c relationship).
Statement A is INCORRECT: For weak electrolyte A, Λ°m CANNOT be obtained by simple extrapolation of the Λm vs √c graph (the curve bends sharply), so Kohlrausch's law of independent migration of ions is used instead.
Statement B is CORRECT: For strong electrolyte B, Debye-Hückel-Onsager equation gives Λm = Λ°m − K√c, so the Λm vs √c graph is a straight line with y-intercept = Λ°m.
Statement C is INCORRECT: For electrolyte B (strong electrolyte), degree of dissociation is essentially 1 (complete dissociation) at all concentrations including infinite dilution — it does NOT approach zero.
Statement D is CORRECT: By Kohlrausch's law, Λ°m for any electrolyte = sum of λ° of individual ions, applicable to both A and B.
So statements A and C are incorrect → 2 incorrect statements.
Statement A is INCORRECT: For weak electrolyte A, Λ°m CANNOT be obtained by simple extrapolation of the Λm vs √c graph (the curve bends sharply), so Kohlrausch's law of independent migration of ions is used instead.
Statement B is CORRECT: For strong electrolyte B, Debye-Hückel-Onsager equation gives Λm = Λ°m − K√c, so the Λm vs √c graph is a straight line with y-intercept = Λ°m.
Statement C is INCORRECT: For electrolyte B (strong electrolyte), degree of dissociation is essentially 1 (complete dissociation) at all concentrations including infinite dilution — it does NOT approach zero.
Statement D is CORRECT: By Kohlrausch's law, Λ°m for any electrolyte = sum of λ° of individual ions, applicable to both A and B.
So statements A and C are incorrect → 2 incorrect statements.
[JEE Main 2023 · 29 Jan · Shift 1]