Conductance - Specific and Molar - UNSOLVED PRACTICE SET
Chapter: Electrochemistry | Topic: Conductance Specific and Molar
CONDUCTANCE - SPECIFIC AND MOLAR - UNSOLVED PRACTICE SET
Topic: Conductance Specific and Molar
Multiple Choice Questions
Q1. The SI unit of conductivity (specific conductance) is:
- S (siemens)
- S·m⁻¹ or S·cm⁻¹
- S·m²·mol⁻¹
- Ω·m
Q2. Molar conductivity (Λm) is defined as:
- κ × V, where V is volume in mL containing 1 mole of electrolyte
- κ / c, where c is concentration in mol/m³
- κ × V, where V is volume in m³ containing 1 mole of electrolyte
- Both (b) and (c) are correct
Q3. The conductivity of a solution depends on:
- The nature of the electrolyte
- The concentration of the electrolyte
- The temperature
- All of the above
Q4. Molar conductivity increases with dilution because:
- The number of ions increases
- The degree of dissociation increases, and interionic attraction decreases
- The volume decreases
- The mass of solute increases
Q5. The limiting molar conductivity (Λ°m) is:
- The molar conductivity at infinite dilution
- The molar conductivity at maximum concentration
- The molar conductivity at 0°C
- The molar conductivity at 100°C
Q6. The cell constant (G*) is defined as:
- l/A, where l is the distance between electrodes and A is the area
- A/l
- l × A
- 1/(l × A)
Short Answer Questions
Q7. Define specific conductance (κ) and molar conductivity (Λm). Write their units and the relationship between them.
Q8. A conductivity cell has electrodes 2 cm apart with an area of 4 cm² each. The measured resistance of 0.1 M KCl solution is 50 Ω. Calculate the cell constant and the conductivity of the solution.
Q9. Why does the conductivity of a strong electrolyte decrease with dilution, while molar conductivity increases?
Q10. The conductivity of 0.01 M NaCl solution at 25°C is 0.00141 S·cm⁻¹. Calculate its molar conductivity.
Q11. Your school lab uses a conductivity meter to test the purity of distilled water. Why does even pure water show some conductivity? What is the approximate value?
Q12. Differentiate between strong electrolytes and weak electrolytes with respect to their molar conductivity behaviour on dilution.
Long Answer Questions
Q13. Discuss conductance and its measurement in detail:
(a) Definition of conductance (G), resistance (R), and their relationship: G = 1/R
(b) Specific conductance (κ) — definition, units, and factors affecting it
(c) Molar conductivity (Λm) and equivalent conductivity (Λeq) — definitions and units
(d) Relationship between κ, Λm, and concentration
(e) Measurement of conductivity using a Wheatstone bridge and conductivity cell
(f) Cell constant and its determination using standard KCl solutions
Q14. Explain the variation of molar conductivity with concentration:
(a) For strong electrolytes — Kohlrausch's law and linear relationship: Λm = Λ°m - A√c
(b) For weak electrolytes — sharp increase on dilution due to increased dissociation
(c) Plot of Λm vs √c for strong electrolytes and Λm vs c for weak electrolytes
(d) Limiting molar conductivity (Λ°m) and its significance
(e) Comparison of Λ°m values for different electrolytes
Q15. Conductivity measurements are essential in Indian industry and healthcare. Discuss:
(a) How TDS (total dissolved solids) meters in Indian homes use conductivity to assess water quality
(b) The role of conductivity monitoring in boiler water treatment in thermal power plants
(c) How blood electrolyte analysers in Indian hospitals use conductivity for rapid diagnosis
(d) The use of conductivity sensors in monitoring river water quality under India's National Water Quality Monitoring Programme
Numerical / Application-Based Problems
Q16. The resistance of a conductivity cell filled with 0.01 M KCl solution is 150 Ω at 25°C. The conductivity of 0.01 M KCl is 0.00141 S·cm⁻¹. The same cell filled with 0.005 M NaOH solution gives a resistance of 250 Ω.
(a) Calculate the cell constant.
(b) Calculate the conductivity of the NaOH solution.
(c) Calculate the molar conductivity of NaOH at this concentration.
Q17. The molar conductivity of 0.01 M CH₃COOH is 16.3 S·cm²·mol⁻¹, while its limiting molar conductivity is 390.7 S·cm²·mol⁻¹.
(a) Calculate the degree of dissociation (α) of acetic acid at this concentration.
(b) Calculate the dissociation constant (Ka) of acetic acid.
(c) Calculate the pH of this acetic acid solution.
Q18. A water quality testing lab in Delhi measures the conductivity of Yamuna river water as 850 μS·cm⁻¹ at 25°C.
(a) Convert this conductivity to S·m⁻¹.
(b) Estimate the TDS (total dissolved solids) in mg/L using the approximate relationship: TDS (mg/L) ≈ 0.64 × κ (μS·cm⁻¹).
(c) The BIS standard for drinking water TDS is 500 mg/L. Assess whether this water is potable and suggest appropriate treatment if needed.