chemistry : class12 Conductivity : Conductance in electrolytic solutions : Electrochemistry MCQ Questions and Answers
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Conductivity
MCQ questions and answers.
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MCQ Questions
1. A conductivity cell has a cell constant of 1.25 cm⁻¹. When filled with an electrolytic solution, its resistance is 250 Ω. What is the conductivity of the solution?
A.
2.00 × 10⁻³ S cm⁻¹
B.
5.00 × 10⁻³ S cm⁻¹
C.
3.125 × 10² S cm⁻¹
D.
2.00 × 10² S cm⁻¹
Correct Answer:
5.00 × 10⁻³ S cm⁻¹
Explanation:
Conductivity κ is given by κ = cell constant/resistance. Therefore, κ = 1.25 cm⁻¹/250 Ω = 5.00 × 10⁻³ S cm⁻¹.
2. A standard KCl solution having conductivity 0.0141 S cm⁻¹ shows a resistance of 100 Ω in a conductivity cell. If the same cell shows a resistance of 150 Ω with an unknown solution, what is the conductivity of the unknown solution?
A.
6.27 × 10⁻³ S cm⁻¹
B.
9.40 × 10⁻³ S cm⁻¹
C.
2.115 × 10⁻² S cm⁻¹
D.
1.41 × 10⁻² S cm⁻¹
Correct Answer:
9.40 × 10⁻³ S cm⁻¹
Explanation:
The cell constant is 0.0141 × 100 = 1.41 cm⁻¹. For the unknown solution, κ = 1.41/150 = 9.40 × 10⁻³ S cm⁻¹.
3. The electrodes of a conductivity cell are 2.0 cm apart and each has an effective area of 0.50 cm². If the resistance of an electrolyte solution is 80 Ω, what is its conductivity?
A.
0.0125 S cm⁻¹
B.
0.0250 S cm⁻¹
C.
0.0500 S cm⁻¹
D.
0.0800 S cm⁻¹
Correct Answer:
0.0500 S cm⁻¹
Explanation:
The cell constant is l/A = 2.0/0.50 = 4.0 cm⁻¹. Hence, κ = cell constant/R = 4.0/80 = 0.0500 S cm⁻¹.
4. An electrolyte solution has a conductivity of 1.20 × 10⁻² S cm⁻¹ and concentration 0.100 mol L⁻¹. What is its molar conductivity?
A.
12.0 S cm² mol⁻¹
B.
120 S cm² mol⁻¹
C.
1.20 × 10³ S cm² mol⁻¹
D.
0.120 S cm² mol⁻¹
Correct Answer:
120 S cm² mol⁻¹
Explanation:
Molar conductivity is Λm = κ × 1000/C, where κ is in S cm⁻¹ and C is in mol L⁻¹. Thus, Λm = (1.20 × 10⁻² × 1000)/0.100 = 120 S cm² mol⁻¹.
5. A solution has a conductivity of 2.5 mS cm⁻¹. What is its conductivity expressed in S m⁻¹?
A.
0.025 S m⁻¹
B.
0.250 S m⁻¹
C.
2.50 S m⁻¹
D.
25.0 S m⁻¹
Correct Answer:
0.250 S m⁻¹
Explanation:
Since 1 S cm⁻¹ equals 100 S m⁻¹, 1 mS cm⁻¹ equals 0.1 S m⁻¹. Therefore, 2.5 mS cm⁻¹ = 0.250 S m⁻¹.
6. A conductivity cell has a cell constant of 0.80 cm⁻¹. The resistance of a solution in this cell is 500 Ω. What is the conductivity of the solution?
A.
6.25 × 10⁻⁴ S cm⁻¹
B.
1.60 × 10⁻³ S cm⁻¹
C.
4.00 × 10⁻³ S cm⁻¹
D.
6.25 × 10² S cm⁻¹
Correct Answer:
1.60 × 10⁻³ S cm⁻¹
Explanation:
Using κ = cell constant/R, κ = 0.80 cm⁻¹/500 Ω = 1.60 × 10⁻³ S cm⁻¹.
7. Two conductivity cells contain the same electrolyte solution. Their cell constants are 1.5 cm⁻¹ and 2.0 cm⁻¹, while their measured resistances are 120 Ω and 300 Ω, respectively. What is the ratio of the conductivities measured by the first and second cells?
A.
0.533
B.
1.250
C.
1.875
D.
2.500
Correct Answer:
1.875
Explanation:
For each cell, κ = cell constant/R. Thus, κ₁/κ₂ = (1.5/120)/(2.0/300) = 1.875.
8. An electrolyte solution produces a conductance of 4.0 × 10⁻³ S in a cell whose electrode separation is 5.0 cm and electrode area is 2.0 cm². What is the conductivity of the solution?
A.
1.6 × 10⁻³ S cm⁻¹
B.
4.0 × 10⁻³ S cm⁻¹
C.
1.0 × 10⁻² S cm⁻¹
D.
2.5 × 10⁻² S cm⁻¹
Correct Answer:
1.0 × 10⁻² S cm⁻¹
Explanation:
Conductivity is κ = G × l/A. Therefore, κ = (4.0 × 10⁻³ S × 5.0 cm)/2.0 cm² = 1.0 × 10⁻² S cm⁻¹.
9. When a dilute aqueous electrolyte solution is heated, its conductivity generally increases primarily because heating
A.
increases the number of electrodes in the solution
B.
decreases the mobility of all ions
C.
increases ionic mobility by lowering solution viscosity
D.
changes the cell constant of the conductivity cell
Correct Answer:
increases ionic mobility by lowering solution viscosity
Explanation:
Conductivity depends on the mobility and concentration of ions. Heating generally lowers solvent viscosity and increases ionic mobility, producing higher conductivity.
10. The molar conductivity of an electrolyte solution is 5.0 × 10⁻³ S m² mol⁻¹, and its concentration is 0.20 mol m⁻³. What is the conductivity of the solution?
A.
1.0 × 10⁻⁵ S m⁻¹
B.
1.0 × 10⁻³ S m⁻¹
C.
2.5 × 10⁻² S m⁻¹
D.
1.0 × 10⁻¹ S m⁻¹
Correct Answer:
1.0 × 10⁻³ S m⁻¹
Explanation:
The relation is κ = Λm × c when Λm is in S m² mol⁻¹ and c is in mol m⁻³. Hence, κ = 5.0 × 10⁻³ × 0.20 = 1.0 × 10⁻³ S m⁻¹.
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