Variation of Conductance with Concentration - UNSOLVED PRACTICE SET
Chapter: Electrochemistry | Topic: Variation of Conductance with Concentration
VARIATION OF CONDUCTANCE WITH CONCENTRATION - UNSOLVED PRACTICE SET
Topic: Variation of Conductance with Concentration
Multiple Choice Questions
Q1. For strong electrolytes, the plot of molar conductivity (Λm) versus the square root of concentration (√c) is:
- A curve
- A straight line with a positive slope
- A straight line with a negative slope
- A parabola
Q2. Kohlrausch's law of independent migration of ions states that:
- The molar conductivity of an electrolyte depends only on the cation
- The limiting molar conductivity of an electrolyte is the sum of the limiting molar conductivities of its constituent ions
- The conductivity of a solution is independent of temperature
- Strong and weak electrolytes behave identically at all concentrations
Q3. The degree of dissociation (α) of a weak electrolyte can be calculated from molar conductivity data using:
- α = Λm / Λ°m
- α = Λ°m / Λm
- α = Λm × Λ°m
- α = Λm - Λ°m
Q4. At infinite dilution, the molar conductivity of CH₃COOH is equal to:
- Λ°(CH₃COOH) = λ°(CH₃COO⁻)
- Λ°(CH₃COOH) = λ°(H⁺) + λ°(CH₃COO⁻)
- Λ°(CH₃COOH) = λ°(H⁺) - λ°(CH₃COO⁻)
- Λ°(CH₃COOH) = λ°(Na⁺) + λ°(CH₃COO⁻)
Q5. The conductivity of a strong electrolyte solution:
- Increases sharply with dilution
- Decreases with dilution due to a decrease in the number of ions per unit volume
- Remains constant with dilution
- First increases, then decreases
Q6. The ionic mobility of H⁺ in aqueous solution is exceptionally high because of:
- Its small size
- The Grotthuss mechanism (proton hopping)
- It's high charge
- Both (a) and (b)
Short Answer Questions
Q7. State Kohlrausch's law of independent migration of ions. How is it useful in determining the limiting molar conductivity of weak electrolytes?
Q8. The molar conductivity at infinite dilution for NaCl, HCl, and CH₃COONa are 126.4, 425.9, and 91.0 S·cm²·mol⁻¹ respectively. Calculate Λ°m for CH₃COOH.
Q9. Why does the conductivity of a solution decrease with dilution, while molar conductivity increases? Explain for both strong and weak electrolytes.
Q10. The limiting molar conductivity of NH₄Cl is 149.6 S·cm²·mol⁻¹ and that of NaOH is 247.7 S·cm²·mol⁻¹. If Λ°m for NaCl is 126.4 S·cm²·mol⁻¹, calculate Λ°m for NH₄OH.
Q11. Your school lab has two bottles — one containing 0.1 M HCl and another 0.1 M CH₃COOH. Both have similar conductivity values at this concentration. Explain why this happens despite HCl being a strong acid and CH₃COOH being a weak acid.
Q12. Why does the plot of Λm vs √c for strong electrolytes deviate from linearity at higher concentrations?
Long Answer Questions
Q13. Discuss the variation of conductance with concentration for electrolytes:
(a) Strong electrolytes — conductivity decreases, molar conductivity increases slightly with dilution
(b) Weak electrolytes — conductivity decreases, molar conductivity increases sharply with dilution
(c) Explanation using degree of dissociation and interionic attraction
(d) Debye-Hückel-Onsager equation for strong electrolytes
(e) Ostwald's dilution law for weak electrolytes
(f) Graphical representation and interpretation for both types
Q14. Explain Kohlrausch's law and its applications:
(a) Statement of Kohlrausch's law of independent migration of ions
(b) Mathematical expression: Λ°m = ν₊λ°₊ + ν₋λ°₋
(c) Application 1: Calculation of Λ°m for weak electrolytes from strong electrolyte data
(d) Application 2: Calculation of degree of dissociation and dissociation constant
(e) Application 3: Determination of ionic product of water
(f) Application 4: Solubility determination of sparingly soluble salts
Q15. Conductivity-concentration relationships guide quality control in Indian industries. Discuss:
(a) How dairy industries use conductivity to detect adulteration in milk (water addition changes conductivity predictably)
(b) The use of conductivity titrations in pharmaceutical manufacturing in India
(c) How conductivity monitoring ensures proper regeneration of ion-exchange resins in water treatment plants
(d) The role of conductometric studies in developing new electrolytes for India's battery research programs
Numerical / Application-Based Problems
Q16. The following data is given at 25°C:
Λ°m(NaCl) = 126.4 S·cm²·mol⁻¹
Λ°m(KCl) = 149.8 S·cm²·mol⁻¹
Λ°m(NaBr) = 128.1 S·cm²·mol⁻¹
(a) Calculate Λ°m(KBr) using Kohlrausch's law.
(b) Calculate the limiting ionic conductivity of K⁺ if λ°(Cl⁻) = 76.3 S·cm²·mol⁻¹.
(c) If the measured Λm of 0.01 M KBr is 145.5 S·cm²·mol⁻¹, calculate the degree of dissociation (assume KBr behaves ideally at this dilution).
Q17. The molar conductivity of 0.05 M CH₃COOH is 7.36 S·cm²·mol⁻¹. The limiting molar conductivities are:
λ°(H⁺) = 349.8 S·cm²·mol⁻¹, λ°(CH₃COO⁻) = 40.9 S·cm²·mol⁻¹
(a) Calculate Λ°m(CH₃COOH).
(b) Calculate the degree of dissociation (α) at 0.05 M.
(c) Calculate the dissociation constant Ka.
(d) Calculate the pH of this solution.
Q18. A dairy cooperative in Gujarat tests milk samples for water adulteration using conductivity.
(a) Pure milk has a conductivity of about 5 mS·cm⁻¹ at 25°C. If 100 mL of milk is mixed with 10 mL of water, predict whether conductivity will increase or decrease and explain.
(b) If the conductivity drops to 4.2 mS·cm⁻¹, estimate the percentage of water added (assume linear relationship for small dilutions).
(c) Design a conductometric method to detect common adulterants (water, urea, detergent) in milk and explain the principle for each.