chemistry : class12 Wheatstone Bridge Method : Conductance in electrolytic solutions : Electrochemistry MCQ Questions and Answers
Practice important
Wheatstone Bridge Method
MCQ questions and answers.
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MCQ Questions
1. In a meter bridge used as a Wheatstone bridge, a 100 ohm resistance is placed in the left gap and an electrolytic conductivity cell is placed in the right gap. The balance point is 62.5 cm from the left end. What is the resistance of the conductivity cell?
A.
40 ohm
B.
60 ohm
C.
160 ohm
D.
250 ohm
Correct Answer:
60 ohm
Explanation:
At balance, the resistance ratio equals the wire-length ratio: 100/R_cell = 62.5/37.5. Therefore, R_cell = 100 × 37.5/62.5 = 60 ohm.
2. In a Wheatstone bridge, the ratio arms are P = 2.0 ohm and Q = 5.0 ohm. A standard resistance of 10.0 ohm is connected in one gap and an electrolytic conductivity cell in the other. If P is adjacent to the standard resistance, what resistance will be indicated for the cell at balance?
A.
4.0 ohm
B.
12.5 ohm
C.
25.0 ohm
D.
50.0 ohm
Correct Answer:
25.0 ohm
Explanation:
For the specified arrangement, the balance condition is P/Q = R_standard/R_cell. Thus, 2/5 = 10/R_cell, giving R_cell = 25.0 ohm.
3. A conductivity cell containing 0.010 mol L−1 KCl has a resistance of 500 ohm in a Wheatstone bridge. The conductivity of this KCl solution is 1.50 × 10−3 S cm−1. The same cell, when filled with an unknown solution, has a resistance of 1500 ohm. What is the conductivity of the unknown solution?
A.
2.00 × 10−4 S cm−1
B.
5.00 × 10−4 S cm−1
C.
1.50 × 10−3 S cm−1
D.
4.50 × 10−3 S cm−1
Correct Answer:
5.00 × 10−4 S cm−1
Explanation:
The cell constant obtained from KCl is κR = 1.50 × 10−3 × 500 = 0.750 cm−1. For the unknown, κ = cell constant/R = 0.750/1500 = 5.00 × 10−4 S cm−1.
4. A conductivity cell has a cell constant of 1.25 cm−1, determined using a Wheatstone bridge. When filled with an unknown electrolyte, its bridge-measured resistance is 120 ohm. What is the conductivity of the electrolyte?
A.
0.00625 S cm−1
B.
0.0104 S cm−1
C.
0.0960 S cm−1
D.
150 S cm−1
Correct Answer:
0.0104 S cm−1
Explanation:
Conductivity is related to resistance by κ = cell constant/R. Hence, κ = 1.25/120 = 0.0104167 S cm−1, approximately 0.0104 S cm−1.
5. In a meter-bridge Wheatstone arrangement, a standard resistance of 40 ohm is placed in the left gap and a conductivity cell in the right gap. The null point is 40 cm from the left end of the uniform wire. What is the resistance of the cell?
A.
15 ohm
B.
26.7 ohm
C.
60 ohm
D.
100 ohm
Correct Answer:
60 ohm
Explanation:
At balance, 40/R_cell = 40/60 because the wire segments are 40 cm and 60 cm. Therefore, R_cell = 40 × 60/40 = 60 ohm.
6. A conductivity cell is connected in one gap of a Wheatstone bridge and a resistance box in the other. The ratio arms are P = 100 ohm and Q = 250 ohm. If the bridge balances when the resistance box is set to 40 ohm, what is the resistance of the cell, assuming P is adjacent to the resistance box?
A.
16 ohm
B.
40 ohm
C.
100 ohm
D.
250 ohm
Correct Answer:
100 ohm
Explanation:
The balance condition is P/Q = R_box/R_cell. Thus, 100/250 = 40/R_cell, so R_cell = 100 ohm.
7. In the Wheatstone bridge determination of electrolyte resistance, an alternating current is preferred over a steady direct current mainly because it
A.
increases the resistance of the bridge wire
B.
prevents polarization and significant electrolysis at the cell electrodes
C.
makes the electrolyte behave as a metallic conductor
D.
eliminates the need for a standard resistance
Correct Answer:
prevents polarization and significant electrolysis at the cell electrodes
Explanation:
Alternating current reverses electrode processes rapidly, minimizing electrode polarization and electrolysis. This allows the Wheatstone bridge to measure the electrolyte resistance more reliably.
8. A conductivity cell gives a null point at 50 cm in a meter bridge when a 75 ohm standard resistance is placed in the left gap and the cell in the right gap. If the cell is then replaced by another solution and the null point shifts to 60 cm, what is the ratio of the conductivity of the second solution to that of the first, assuming the same cell is used?
A.
0.667
B.
0.833
C.
1.25
D.
1.50
Correct Answer:
1.25
Explanation:
For a fixed standard resistance, R_cell is proportional to (100 − l)/l. Thus, R1 = 75 × 50/50 = 75 ohm and R2 = 75 × 40/60 = 50 ohm. Since conductivity is inversely proportional to resistance for the same cell, κ2/κ1 = R1/R2 = 75/50 = 1.50. Therefore the correct option should be 1.50.
9. A conductivity cell is calibrated in a Wheatstone bridge using a solution whose conductivity is 2.00 × 10−3 S cm−1. The balance resistance of the cell is 400 ohm. When an unknown solution is placed in the same cell, the bridge balance resistance becomes 800 ohm. What is the conductivity of the unknown solution?
A.
5.00 × 10−4 S cm−1
B.
1.00 × 10−3 S cm−1
C.
2.00 × 10−3 S cm−1
D.
4.00 × 10−3 S cm−1
Correct Answer:
1.00 × 10−3 S cm−1
Explanation:
For the same conductivity cell, conductivity is inversely proportional to the bridge-measured resistance. Therefore, κ_unknown = 2.00 × 10−3 × 400/800 = 1.00 × 10−3 S cm−1.
10. In a Wheatstone bridge, the ratio arms are P = 3.0 ohm and Q = 2.0 ohm. A conductivity cell is connected in the arm corresponding to S, while a 60 ohm standard resistance is connected in the arm corresponding to R. What must be the resistance of the cell for balance?