ECAT — Engineering College Admission Test (UET)

ECAT Chemistry — Chemical Bonding (Set 2)

Take the ECAT Chemistry — Chemical Bonding (Set 2): 30 multiple-choice questions (40 minutes) with instant scoring and a full answer review. Covers 30…

What this test covers

30 ECAT Chemistry

Sample questions with answers

The first 5 questions of this test, with the correct answer and explanation.

Q1. The shape and bond angle of the BF₃ molecule are:
- A. Trigonal planar, 120° ✓
- B. Trigonal pyramidal, 107°
- C. T-shaped, 90°
- D. Tetrahedral, 109.5°
Answer: A. Trigonal planar, 120°
Explanation: B has three bond pairs and no lone pair (sp²), so the molecule is trigonal planar with 120° angles.
Q2. The hybridization of beryllium in gaseous BeCl₂ and the shape of the molecule are:
- A. sp², bent
- B. sp², trigonal planar
- C. sp³, tetrahedral
- D. sp, linear ✓
Answer: D. sp, linear
Explanation: Be has two bond pairs and no lone pairs; two sp hybrid orbitals point 180° apart, giving a linear molecule.
Q3. The hydronium ion, H₃O⁺, has the shape:
- A. Tetrahedral
- B. Bent
- C. Trigonal pyramidal ✓
- D. Trigonal planar
Answer: C. Trigonal pyramidal
Explanation: O in H₃O⁺ has three bond pairs and one lone pair (sp³), so like NH₃ it is trigonal pyramidal.
Q4. In but-1-en-3-yne, CH₂=CH–C≡CH, how many carbon atoms are sp hybridized?
- A. 2 ✓
- B. 3
- C. 1
- D. 4
Answer: A. 2
Explanation: The two carbons of the C≡C triple bond are sp; the two carbons of the C=C double bond are sp².
Q5. How many σ and π bonds are present in but-2-enal, CH₃–CH=CH–CHO?
- A. 10 σ and 2 π ✓
- B. 9 σ and 2 π
- C. 8 σ and 3 π
- D. 11 σ and 2 π
Answer: A. 10 σ and 2 π
Explanation: σ: 6 C–H + 2 C–C + 1 (C=C) + 1 (C=O) = 10; π: one in C=C and one in C=O = 2.

The other 25 questions

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Q6. According to MO theory, the bond order of N₂⁺ is:
- A. 2
- B. 3
- C. 1.5
- D. 2.5
Q7. According to MO theory, the peroxide ion O₂²⁻ has:
- A. Bond order 1 and is diamagnetic
- B. Bond order 2 and is paramagnetic
- C. Bond order 1.5 and is paramagnetic
- D. Bond order 3 and is diamagnetic
Q8. Which molecule is isoelectronic with N₂ and has the same bond order of 3?
- A. O₂
- B. CO
- C. CN
- D. NO
Q9. HF has an observed dipole moment of 1.82 D and a bond length of 0.917 Å. Taking the electronic charge as 4.8 D per Å, its percentage ionic character is about:
- A. 62%
- B. 41%
- C. 88%
- D. 21%
Q10. NH₃ has a much larger dipole moment than NF₃ although both are pyramidal. This is because:
- A. NH₃ is planar
- B. N–F bonds are non-polar
- C. In NH₃ the lone-pair moment adds to the N–H bond moments, while in NF₃ it opposes the N–F bond moments
- D. NF₃ has no lone pair
Q11. Which compound is expected to be the most ionic?
- A. HCl
- B. CsF
- C. BeCl₂
- D. LiI
Q12. The second ionization energy of sodium is about nine times its first ionization energy because:
- A. Sodium has a small nuclear charge
- B. Sodium is a non-metal
- C. The second electron must be removed from the stable, inner 2p⁶ shell of Na⁺
- D. The 3s electron is very tightly held
Q13. The second electron affinity of oxygen (O⁻ + e⁻ → O²⁻) is:
- A. Large and negative (exothermic)
- B. Positive (energy must be absorbed)
- C. Equal to the first electron affinity
- D. Zero
Q14. Which cation has the greatest polarizing power?
- A. K⁺
- B. Na⁺
- C. Mg²⁺
- D. Al³⁺
Q15. Solid NaCl does not conduct electricity but molten NaCl does, because:
- A. In the molten state the Na⁺ and Cl⁻ ions are free to move
- B. Melting converts the ionic bonds into covalent bonds
- C. Molten NaCl contains molecules
- D. Melting creates free electrons
Q16. The C=C bond energy (614 kJ mol⁻¹) is less than twice the C–C bond energy (348 kJ mol⁻¹) because:
- A. A π bond is stronger than a σ bond
- B. The C=C bond is longer than C–C
- C. Carbon is sp³ in ethene
- D. A π bond is weaker than a σ bond due to less effective sideways overlap
Q17. Given covalent radii C = 77 pm and Cl = 99 pm, the expected C–Cl bond length is about:
- A. 154 pm
- B. 176 pm
- C. 22 pm
- D. 198 pm
Q18. The hybridization of phosphorus in PCl₅ and the bond angles present are:
- A. sp³; 109.5° only
- B. sp³d²; 90° only
- C. sp³d; 90° and 120°
- D. sp³d; 120° and 180° only
Q19. In the adduct H₃N→BF₃, which statement is correct?
- A. The bond is ionic
- B. Both atoms donate one electron each
- C. N donates its lone pair into the empty orbital of B
- D. B donates a lone pair to N
Q20. o-Nitrophenol is more volatile (lower boiling point) than p-nitrophenol because:
- A. o-Nitrophenol is ionic
- B. o-Nitrophenol forms intramolecular hydrogen bonds, while p-nitrophenol forms intermolecular hydrogen bonds
- C. o-Nitrophenol has a higher molar mass
- D. p-Nitrophenol has no –OH group
Q21. BF₃ is planar while NF₃ is pyramidal. The reason is that:
- A. BF₃ has a lone pair on boron
- B. B is more electronegative than N
- C. F atoms repel more strongly in NF₃
- D. N in NF₃ has a lone pair, giving four electron pairs around it
Q22. Which order of radii for the isoelectronic species S²⁻, Cl⁻, K⁺ and Ca²⁺ is correct?
- A. Cl⁻ > S²⁻ > K⁺ > Ca²⁺
- B. Ca²⁺ > K⁺ > Cl⁻ > S²⁻
- C. K⁺ > Ca²⁺ > S²⁻ > Cl⁻
- D. S²⁻ > Cl⁻ > K⁺ > Ca²⁺
Q23. Across period 3 from Na to Cl, the atomic radius generally:
- A. Increases because more shells are added
- B. Decreases because the nuclear charge increases while electrons enter the same shell
- C. Stays constant
- D. Increases because shielding increases sharply
Q24. The σ bond in an HCl molecule is formed by the overlap of:
- A. 2p of H with 3p of Cl
- B. 1s of H with 3s of Cl
- C. Sideways overlap of two p orbitals
- D. 1s of H with 3p of Cl
Q25. The enthalpy change for CH₄(g) → C(g) + 4H(g) is +1664 kJ mol⁻¹. The average C–H bond energy is:
- A. 416 kJ mol⁻¹
- B. 333 kJ mol⁻¹
- C. 832 kJ mol⁻¹
- D. 1664 kJ mol⁻¹
Q26. Using bond energies (kJ mol⁻¹) C=C 614, H–H 436, C–C 348, C–H 413, ΔH for C₂H₄ + H₂ → C₂H₆ is:
- A. +124 kJ mol⁻¹
- B. −124 kJ mol⁻¹
- C. −537 kJ mol⁻¹
- D. −289 kJ mol⁻¹
Q27. The SI-related unit of dipole moment, the debye (D), is equal to:
- A. 1 × 10⁻¹⁰ C m
- B. 1.6 × 10⁻¹⁹ C m
- C. 3.336 × 10⁻³⁰ C m
- D. 6.022 × 10⁻²³ C m
Q28. Which statement about hybrid orbitals is correct?
- A. Hybrid orbitals of an atom have different energies
- B. The number of hybrid orbitals formed equals the number of atomic orbitals mixed
- C. Only s and d orbitals can hybridize
- D. Hybrid orbitals form π bonds by sideways overlap
Q29. The F–B–F bond angle in BF₃ is 120°, but in BF₄⁻ it is about 109.5°. This change is because boron:
- A. Changes from sp³ to sp²
- B. Gains a lone pair in BF₄⁻
- C. Loses an electron
- D. Changes from sp² to sp³ hybridization on accepting an F⁻ ion
Q30. Which molecule has a non-zero dipole moment?
- A. CCl₄
- B. CO₂
- C. CHCl₃
- D. BF₃