JEE Main · 2024 · Shift-IImediumEC-099

Which out of the following is a correct equation to show change in molar conductivity with respect to concentration for…

Electrochemistry · Class 12 · JEE Main Previous Year Question

Question

Which out of the following is a correct equation to show change in molar conductivity with respect to concentration for a weak electrolyte, if the symbols carry their usual meaning:

Options
  1. a

    ΛmΛm0+AC1/2=0\Lambda_m - \Lambda_m^0 + AC^{1/2} = 0

  2. b

    Λm2CKaΛm02+KaΛmΛm0=0\Lambda_m^2 C - K_a \Lambda_m^{0^2} + K_a \Lambda_m \Lambda_m^0 = 0

  3. c

    Λm2C+KaΛm02KaΛmΛm0=0\Lambda_m^2 C + K_a \Lambda_m^{0^2} - K_a \Lambda_m \Lambda_m^0 = 0

  4. d

    ΛmΛm0AC1/2=0\Lambda_m - \Lambda_m^0 - AC^{1/2} = 0

Correct Answerc

Λm2C+KaΛm02KaΛmΛm0=0\Lambda_m^2 C + K_a \Lambda_m^{0^2} - K_a \Lambda_m \Lambda_m^0 = 0

Detailed Solution

Strategy: Use Ostwald's Dilution Law combined with the definition of \degree of dissociation (α=Λm/Λm\alpha = \Lambda_m / \Lambda_m^\circ) to derive an relationship between concentration (CC) and molar conductivity.

Step 1: Start with KaK_a Ka=Cα21αK_a = \frac{C\alpha^2}{1-\alpha}

Step 2: Substitute α\alpha Ka=C(Λm/Λm0)21(Λm/Λm0)=CΛm2Λm0(Λm0Λm)K_a = \frac{C(\Lambda_m / \Lambda_m^0)^2}{1 - (\Lambda_m / \Lambda_m^0)} = \frac{C\Lambda_m^2}{\Lambda_m^0 (\Lambda_m^0 - \Lambda_m)}

Step 3: Rearrange into the target form KaΛm0(Λm0Λm)=CΛm2K_a \Lambda_m^0 (\Lambda_m^0 - \Lambda_m) = C\Lambda_m^2 Ka(Λm0)2KaΛmΛm0=CΛm2K_a (\Lambda_m^0)^2 - K_a \Lambda_m \Lambda_m^0 = C\Lambda_m^2 CΛm2+KaΛmΛm0Ka(Λm0)2=0C\Lambda_m^2 + K_a \Lambda_m \Lambda_m^0 - K_a (\Lambda_m^0)^2 = 0

Note based on the signs in the options: CΛm2+Ka(Λm0)2KaΛmΛm0=0C\Lambda_m^2 + K_a (\Lambda_m^0)^2 - K_a \Lambda_m \Lambda_m^0 = 0 Matches Option (c).

Answer: (c)\boxed{\text{Answer: (c)}}

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