chemistry : class11 Bond Dipole Addition : Polar character of covalent bond : Chemical Bonding and Molecular Structure MCQ Questions and Answers
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Bond Dipole Addition
MCQ questions and answers.
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MCQ Questions
1. Two identical bond dipoles of magnitude μ in a bent AB2 molecule make an angle of 104.5° with each other. What is the magnitude of the resultant molecular dipole moment?
A.
0.89μ
B.
1.23μ
C.
1.67μ
D.
2.00μ
Correct Answer:
1.23μ
Explanation:
For two equal vectors separated by angle θ, the resultant is 2μ cos(θ/2). Thus, μ_resultant = 2μ cos(52.25°) ≈ 1.23μ.
2. In a linear molecule A–B–C, the A–B bond dipole has magnitude 3.0 D and the B–C bond dipole has magnitude 2.0 D. If the two bond dipoles are oppositely directed along the molecular axis, what is the molecular dipole moment?
A.
1.0 D
B.
2.0 D
C.
5.0 D
D.
6.0 D
Correct Answer:
1.0 D
Explanation:
Because the bond dipoles are collinear and oppositely directed, their vector sum is the difference of their magnitudes: 3.0 D − 2.0 D = 1.0 D.
3. Three identical bond dipoles in a planar molecule are symmetrically arranged, with 120° between every pair of adjacent dipoles. What is the resultant molecular dipole moment?
A.
μ
B.
√2μ
C.
2μ
D.
0
Correct Answer:
0
Explanation:
The three equal bond-dipole vectors are separated by 120° and form a closed vector triangle. Therefore, their vector sum is zero.
4. Four identical bond dipoles in a tetrahedral molecule point from a central atom toward four identical surrounding atoms. If the tetrahedral arrangement is perfectly symmetrical, what is the resultant molecular dipole moment?
A.
μ
B.
2μ
C.
2√2μ
D.
0
Correct Answer:
0
Explanation:
The four equal bond-dipole vectors are symmetrically directed toward the vertices of a tetrahedron. Their vector components cancel in all three dimensions, giving zero resultant dipole moment.
5. Two bond dipoles have equal magnitudes of 2.0 D and are inclined at 60° to each other. What is the magnitude of their resultant?
A.
2.0 D
B.
2√2 D
C.
2√3 D
D.
4.0 D
Correct Answer:
2√3 D
Explanation:
Using vector addition, μ_resultant = √(μ² + μ² + 2μ² cos60°) = √(4 + 4 + 4) D = 2√3 D.
6. Two bond dipoles in a molecule have magnitudes 5.0 D and 3.0 D, and the angle between them is 120°. What is the magnitude of their resultant dipole moment?
A.
√19 D
B.
√34 D
C.
4.0 D
D.
8.0 D
Correct Answer:
√19 D
Explanation:
The resultant is √(μ1² + μ2² + 2μ1μ2 cos120°) = √(25 + 9 − 15) D = √19 D.
7. A molecule contains two equal bond dipoles of magnitude μ arranged at an angle of 180°. Which statement correctly describes their vector addition?
A.
The resultant is 2μ and lies along either bond direction
B.
The resultant is μ and is perpendicular to the bond axis
C.
The resultant is √2μ and bisects the angle between the bonds
D.
The resultant is zero because the dipoles are equal and opposite
Correct Answer:
The resultant is zero because the dipoles are equal and opposite
Explanation:
For two equal dipoles pointing in exactly opposite directions, every vector component of one is cancelled by the corresponding component of the other, so the resultant is zero.
8. In an ideal trigonal-planar molecule, three identical bond dipoles are directed from the central atom toward the surrounding atoms. If each bond dipole has magnitude 1.5 D, what is the molecular dipole moment?
A.
0 D
B.
1.5 D
C.
3.0 D
D.
4.5 D
Correct Answer:
0 D
Explanation:
The three identical dipoles are separated by 120° in one plane. Their vector sum is zero because their equal components cancel symmetrically.
9. Two bond dipoles of magnitudes 4.0 D and 4.0 D are perpendicular to each other. What are the magnitude and direction of the resultant dipole?
A.
4.0 D, along one of the dipoles
B.
4√2 D, along the angle bisector
C.
8.0 D, along the angle bisector
D.
0 D, because the dipoles are not collinear
Correct Answer:
4√2 D, along the angle bisector
Explanation:
For perpendicular equal vectors, the resultant magnitude is √(4² + 4²) = 4√2 D. Equal perpendicular components make the resultant lie along the angle bisector.
10. Three identical bond dipoles of magnitude μ have pairwise angles of 90°, 90°, and 180°. What is the magnitude of their resultant dipole moment?
A.
0
B.
μ
C.
√2μ
D.
2μ
Correct Answer:
√2μ
Explanation:
Choose the two dipoles separated by 90° as perpendicular vectors. The third dipole is opposite to one of them, so it cancels that dipole. The remaining perpendicular pair has resultant magnitude √2μ.
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