1. ⇒ (NEET 2023 Manipur )

Molar conductance of an electrolyte increase with dilution according to the equation:

$Λ_{m} = Λ_{m}^{\circ} - A \sqrt{c}$

Which of the following statements are true?

(A) This equation applies to both strong and weak electrolytes.

(B) Value of the constant $A$ depends upon the nature of the solvent.

(C) Value of constant $A$ is same for both ${BaCl}_{2}$ and ${MgSO}_{4}$

(D) Value of constant $A$ is same for both ${BaCl}_{2}$ and $Mg (OH)_{2}$

Choose the most appropriate answer from the options given below:

(A) (A) and (B) only

(B) (A), (B) and (C) only

(C) (B) and (C) only

(D) (B) and (D) only

Correct Answer is Option (D)

B and D statement are correct.

2. ⇒ (NEET 2023 )

The conductivity of centimolar solution of $KCl$ at $25^{\circ} C$ is $0.0210 {ohm}^{- 1} {cm}^{- 1}$ and the resistance of the cell containing the solution at $25^{\circ} C$ is $60 ohm$ . The value of cell constant is -

(A) $3.28 {cm}^{- 1}$

(B) $1.26 {cm}^{- 1}$

(C) $3.34 {cm}^{- 1}$

(D) $1.34 {cm}^{- 1}$

Correct Answer is Option (B)

Centimolar solution $= \frac{1}{100} M = 0.01 M$

Conductivity $(k) = 0.0210 {ohm}^{- 1} {cm}^{- 1}$

Resistance $(R) = 60 ohm$

$k = \frac{1}{R} (\frac{ℓ}{A})$

$\Rightarrow 0.0210 = \frac{1}{60} (\frac{ℓ}{A}) \Rightarrow \frac{ℓ}{A} = 1.26 {cm}^{- 1}$

3. ⇒ (NEET 2021 )

The molar conductance of NaCl, HCl and CH₃COONa at infinite dilution are 126.45, 426.16 and 91.0 S cm² mol^{$-$ 1} respectively. The molar conductance of CH₃COOH at infinite dilution is. Choose the right option for your answer.

(A) 540.48 S cm² mol^{$-$ 1}

(B) 201.28 S cm² mol^{$-$ 1}

(C) 390.71 S cm² mol^{$-$ 1}

(D) 698.28 S cm² mol^{$-$ 1}

Correct Answer is Option (C)

According to Kohlrausch law of independent migration of ions.

$Λ_{m}^{o} (C H_{3} C O O H)$

$= Λ_{m}^{o} (C H_{3} C O O N a) + Λ_{m}^{o} (H C l) - Λ_{m}^{o} (N a C l)$

= 91.0 S cm² mol^{$-$ 1} + 426.16 S cm² mol^{$-$ 1} $-$ 126.45 S cm² mol^{$-$ 1}

= 390.71 S cm² mol^{$-$ 1}

4. ⇒ (NEET 2016 Phase 2 )

The molar conductivity of a 0.5 mol/dm³ solution of AgNO₃ with electrolytic conductivity of 5.76 $\times$ 10^{$-$ 3} S cm^{$-$ 1} at 298 K is

(A) 2.88 S cm²/mol

(B) 11.52 S cm²/mol

(C) 0.086 S cm²/mol

(D) 28.8 S cm²/mol

Correct Answer is Option (B)

$Λ_{m} = \frac{κ \times 1000}{M o l a l i t y}$

= $\frac{5.76 \times 10^{- 3} \times 1000}{0.5}$

= 11.52 S cm²/mol

5. ⇒ (NEET 2013 )

At 25^oC molar conductance of 0.1 molar aqueous solution of ammonium hydroxide is 9.54 ohm^{$-$ 1} cm² mol^{$-$ 1} and at infinite dilution its molar conductance is 238 ohm^{$-$ 1} cm² mol^{$-$ 1}. The degree of ionisation of ammonium hydroxide at the same concentration and temperature is

(A) 4.008%

(B) 40.800%

(C) 2.080%

(D) 20.800%

Correct Answer is Option (A)

Degree of dissociation( $α$ ) = $\frac{9.54}{238}$ = 0.04008 = 4.008%

6. ⇒ (AIPMT 2010 Prelims )

An increase in equivalent conductance of a strong electrolyte with dilution is mainly due to

(A) increase in ionic mobility of ions

(B) 100% ionisation of electrolyte at normal dilution

(C) increase in both i.e., number of ions and ionic mobility of ions

(D) increase in number of ions.

Correct Answer is Option (A)

Dilution of strong electrolytes increases ionisation, hence ionic mobility of ions increases which in turn increases equivalent conductance of the solution.

7. ⇒ (AIPMT 2009 )

The equivalent conductance of M/32 solution of a weak monobasic acid is 8.0 mho cm² and at infinite dilution is 400 mho cm². The dissociation constant of this acid is

(A) 1.25 $\times$ 10^{$-$ 6}

(B) 6.25 $\times$ 10^{$-$ 4}

(C) 1.25 $\times$ 10^{$-$ 4}

(D) 1.25 $\times$ 10^{$-$ 5}

Correct Answer is Option (D)

The degree of dissociation ( $α$ )

$α$ = $\frac{8}{400}$ = 2 $\times$ 10^-2

From Ostwald’s dilution law for weak monobasic acid, we have

k_c = C $α$ ²

= $\frac{1}{32} \times {(2 \times 10^{- 2})}^{2}$

= 1.25 $\times$ 10^-5

8. ⇒ (AIPMT 2008 )

Kohlrausch's law states that at

(A) Infinite dilution, each ion makes definite contribution to conductance of an electrolyte whatever be the nature of the other ion of the electrolyte

(B) Infinite dilution, each ion makes definite contribution to equivalent conductance of an electrolyte, whatever be the nature of the other ion of the electrolyte

(C) Finite dilution, each ion makes definite contribution to equivalent conductance of an electrolyte, whatever be the nature of the other ion of the electrolyte

(D) Infinite dilution each ion makes definite contribution to equivalent conductance of an electrolyte depending on the nature of the other ion of the electrolyte.

Correct Answer is Option (A)

Kohlrausch’s law states that the equivalent conductance of an electrolyte at infinite dilution is equal to the sum of the equivalent conductance of the component ions.

$λ$ _$\infty$ = $λ$ _a + $λ$ _c

where, $λ$ _a = equivalent conductance of the anion

$λ$ _c = equivalent conductance of the cation.

9. ⇒ (AIPMT 2000 )

Equivalent conductances of Ba²⁺ and Cl^$-$ ions are 127 and 76 ohm^{$-$ 1} cm^{$-$ 1} eq^{$-$ 1} respectively. Equivalent conductance of BaCl₂ at infinite dilution is

(A) 139.5

(B) 101.5

(C) 203

(D) 279

Correct Answer is Option (A)

According to Kohlrausch’s law, the equivalent conductance of BaCl₂ at infinite dilution,

$λ$ _$\infty$ of BaCl₂ = $\frac{1}{2}$ $λ$ _$\infty$ of Ba²⁺ + $λ$ _$\infty$ of Cl^-

$\Rightarrow$ $λ$ _$\infty$ of BaCl₂ = $\frac{1}{2} \times 127 + 76$ = 139 5

⇒Electrochemistry

Topic 3 : Conductance of Electrolytic Solution