Specific, equivalent and molar conductivity; Kohlrausch's law — NEET & JEE Questions

Question 1 · difficulty L1 · recall

Molar conductivity is the conductance of the volume of solution containing

• A. one mole of electrolyte
• B. one gram of solvent
• C. one litre of pure water
• D. one equivalent of solvent

Question 2 · difficulty L2 · understanding

On dilution of an electrolyte solution, the specific conductivity generally

• A. increases because ions move farther apart
• B. decreases because the number of ions per unit volume decreases
• C. remains exactly constant
• D. becomes infinite

Question 3 · difficulty L2 · understanding

On dilution, molar conductivity of an electrolyte generally

• A. decreases
• B. increases
• C. remains zero
• D. becomes independent of ion mobility

Question 4 · difficulty L2 · understanding

Kohlrausch's law at infinite dilution states that the limiting molar conductivity of an electrolyte is

• A. the sum of independent limiting ionic contributions of its ions
• B. always zero
• C. equal only to the cation contribution
• D. independent of which ions are present

Question 5 · difficulty L3 · application

A solution has conductivity $\kappa=1.0\times10^{-3}\,\text{S cm}^{-1}$ and concentration $0.010\,\text{mol L}^{-1}$. What is its molar conductivity?

• A. 10 S cm² mol⁻¹
• B. 50 S cm² mol⁻¹
• C. 100 S cm² mol⁻¹
• D. 1000 S cm² mol⁻¹

Question 6 · difficulty L3 · application

At infinite dilution, $\lambda^\circ_{Na^+}=50.1$ and $\lambda^\circ_{Cl^-}=76.3$ S cm² mol⁻¹. What is $\Lambda_m^\circ$ for NaCl?

• A. 26.2 S cm² mol⁻¹
• B. 50.1 S cm² mol⁻¹
• C. 76.3 S cm² mol⁻¹
• D. 126.4 S cm² mol⁻¹

Question 7 · difficulty L3 · application

The molar conductivity of a weak electrolyte at a certain concentration is 40 S cm² mol⁻¹ and its limiting molar conductivity is 400 S cm² mol⁻¹. Estimate its degree of dissociation.

• A. 0.01
• B. 0.10
• C. 0.40
• D. 10

Question 8 · difficulty L3 · application

Which electrolyte is expected to show a much sharper increase in molar conductivity on dilution?

• A. A weak electrolyte such as acetic acid
• B. A strong electrolyte such as KCl
• C. A non-electrolyte such as glucose
• D. A metal wire

Question 9 · difficulty L4 · application

At infinite dilution, $\Lambda_m^\circ(HCl)=426$, $\Lambda_m^\circ(NaCl)=126$ and $\Lambda_m^\circ(NaA)=91$ S cm² mol⁻¹. Using Kohlrausch's law, estimate $\Lambda_m^\circ(HA)$ for the weak acid HA.

• A. 299 S cm² mol⁻¹
• B. 391 S cm² mol⁻¹
• C. 517 S cm² mol⁻¹
• D. 643 S cm² mol⁻¹

Question 10 · difficulty L4 · application

A 0.020 M solution has conductivity $2.5\times10^{-3}\,\text{S cm}^{-1}$. What is its molar conductivity?

• A. 12.5 S cm² mol⁻¹
• B. 50 S cm² mol⁻¹
• C. 125 S cm² mol⁻¹
• D. 500 S cm² mol⁻¹