chemistry : class12 Kohlrausch Law : Conductance in electrolytic solutions : Electrochemistry MCQ Questions and Answers
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Kohlrausch Law
MCQ questions and answers.
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MCQ Questions
1. Kohlrausch's law states that at infinite dilution, the molar conductivity of an electrolyte is equal to:
A.
The sum of the conductivities of the solvent and solute
B.
The sum of the individual contributions of its ions
C.
The difference between ionic conductivities
D.
The product of the ionic conductivities
Correct Answer:
The sum of the individual contributions of its ions
Explanation:
Kohlrausch's law states that each ion contributes independently to the total limiting molar conductivity of an electrolyte.
2. The limiting molar conductivity of sodium chloride according to Kohlrausch's law is represented by:
A.
Λ°m(NaCl) = λ°(Na+) + λ°(Cl−)
B.
Λ°m(NaCl) = λ°(Na+) − λ°(Cl−)
C.
Λ°m(NaCl) = λ°(Na+) × λ°(Cl−)
D.
Λ°m(NaCl) = λ°(Na+) ÷ λ°(Cl−)
Correct Answer:
Λ°m(NaCl) = λ°(Na+) + λ°(Cl−)
Explanation:
For NaCl, the limiting molar conductivity is the sum of the limiting ionic conductivities of Na+ and Cl−.
3. Which quantity is added for individual ions in Kohlrausch's law?
A.
Limiting ionic conductivity
B.
Resistance
C.
Cell constant
D.
Concentration
Correct Answer:
Limiting ionic conductivity
Explanation:
Kohlrausch's law uses the limiting ionic conductivities of the cation and anion to calculate limiting molar conductivity.
4. If λ°(K+) = 73.5 S cm² mol⁻¹ and λ°(Cl−) = 76.3 S cm² mol⁻¹, what is Λ°m(KCl)?
A.
2.8 S cm² mol⁻¹
B.
73.5 S cm² mol⁻¹
C.
149.8 S cm² mol⁻¹
D.
5614.1 S cm² mol⁻¹
Correct Answer:
149.8 S cm² mol⁻¹
Explanation:
By Kohlrausch's law, Λ°m(KCl) = λ°(K+) + λ°(Cl−) = 73.5 + 76.3 = 149.8 S cm² mol⁻¹.
5. According to Kohlrausch's law, ionic migration at infinite dilution is considered to be:
A.
Dependent on the other ion present
B.
Independent of the other ion present
C.
Zero for both ions
D.
Equal for all ions
Correct Answer:
Independent of the other ion present
Explanation:
At infinite dilution, ions are sufficiently far apart, so each ion makes an independent contribution to conductivity.
6. Which expression gives the limiting molar conductivity of calcium chloride?
A.
Λ°m(CaCl₂) = λ°(Ca²⁺) + 2λ°(Cl−)
B.
Λ°m(CaCl₂) = 2λ°(Ca²⁺) + λ°(Cl−)
C.
Λ°m(CaCl₂) = λ°(Ca²⁺) − 2λ°(Cl−)
D.
Λ°m(CaCl₂) = λ°(Ca²⁺) × 2λ°(Cl−)
Correct Answer:
Λ°m(CaCl₂) = λ°(Ca²⁺) + 2λ°(Cl−)
Explanation:
One Ca²⁺ ion and two Cl− ions are present in calcium chloride, so their limiting ionic conductivities are added with these coefficients.
7. If λ°(Na+) = 50.1 S cm² mol⁻¹ and λ°(Cl−) = 76.3 S cm² mol⁻¹, the limiting molar conductivity of NaCl is:
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
Correct Answer:
126.4 S cm² mol⁻¹
Explanation:
Using Kohlrausch's law, Λ°m(NaCl) = 50.1 + 76.3 = 126.4 S cm² mol⁻¹.
8. Kohlrausch's law is mainly used to calculate the limiting molar conductivity of:
A.
Only strong electrolytes
B.
Only gases
C.
Weak electrolytes using ionic conductivities of suitable strong electrolytes
D.
Non-electrolytes without any measurements
Correct Answer:
Weak electrolytes using ionic conductivities of suitable strong electrolytes
Explanation:
The law allows the limiting molar conductivity of weak electrolytes to be obtained by combining ionic contributions from suitable strong electrolytes.
9. The limiting molar conductivity of an electrolyte depends on the:
A.
Sum of the limiting ionic conductivities of its ions
B.
Colour of the electrolyte solution
C.
Shape of the conductivity cell only
D.
Mass of the solvent only
Correct Answer:
Sum of the limiting ionic conductivities of its ions
Explanation:
Kohlrausch's law directly relates limiting molar conductivity to the sum of the independent limiting ionic conductivities.
10. If λ°(H+) = 349.6 S cm² mol⁻¹ and λ°(Cl−) = 76.3 S cm² mol⁻¹, what is the limiting molar conductivity of HCl?
A.
273.3 S cm² mol⁻¹
B.
349.6 S cm² mol⁻¹
C.
425.9 S cm² mol⁻¹
D.
26.3 S cm² mol⁻¹
Correct Answer:
425.9 S cm² mol⁻¹
Explanation:
According to Kohlrausch's law, Λ°m(HCl) = λ°(H+) + λ°(Cl−) = 349.6 + 76.3 = 425.9 S cm² mol⁻¹.
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