midterm 2, 2016 PDF

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Chemistry 101, Mid-Term Test 2 Version A Fall 2016 Version A This test consists entirely of multiple choice questions and is worth 25 marks. There is one mark per question. The answers for the 25 questions must be coded on the optical sense form (bubble sheet) using a PEN or SOFT PENCIL. Select the BEST response for each question below. 1. Of the interhalogen compounds ICl, ICl3 and ICl5, which statement concerning their molecular dipole moments is correct? A. B. C. D. E.

None have a net molecular dipole. All have a net molecular dipole. Only ICl has a net molecular dipole. Only ICl3 has a net molecular dipole. Only ICl and ICl3 have net molecular dipoles.

2. In a Valence Bond description of bonding, the molecule H3C–C≡C–H has the following total number of hybridized orbitals: A. B. C. D. E.

2 4 6 8 10

3. Which of the following statements is/are CORRECT for metallic bonding?

A. B. C. D. E.

i) Bonding electrons in metals are free to move from one bonding region to another. ii) Bonding theory for metals must include highly directional bonds as for molecules. iii) The energy gap (band gap) between bonding and antibonding molecular orbitals is largest for an insulator. iv) There are no antibonding molecular orbitals for a semiconductor. I only I and II II and III I and III II and IV

4. The molecular geometry (shape) of a molecule with the general formula AB2 can be: A. B. C. D. E.

linear or bent linear or trigonal planar T-shaped only linear or T-shaped trigonal planar only

5. Assuming that the octet rule applies to all these structures, which of the molecules: HC≡CH, HCN, CO has a non-zero formal charge on carbon? A. B. C. D. E.

HC≡CH HCN CO HCN and CO none of them

6. A Lewis structure of Ibuprofen is shown below without its lone pairs of electrons. The approximatebond angle (in degrees, °) labeled “a”, “b” and “c” in the drawing are, respectively: A. B. C. D. E.

120, 120, 120 120, 109, 180 180, 120, 120 109, 120, 109 109, 109, 120

Carry out a VSEPR analysis of the molecule BrF5 and answer questions 7 and 8 below. 7. The number of electron pairs (bonding and non-bonding) around the Br atom is A. B. C. D. E.

5 bonding, 0 non-bonding 5 bonding, 1 non-bonding 6 bonding, 0 non-bonding 6 bonding, 1 non-bonding 5 bonding, 2 non-bonding

8. How many F–Br–F bond angles are approximately 90° in BrF5? A. B. C. D. E.

0 1 8 6 4

9. The molecular shape of the PHCl2 molecule is? A. B. C. D. E.

Trigonal planar Trigonal pyramidal Bent T-shaped Tetrahedral

10. Which of the following statements about formal charges is INCORRECT? A. In calculating formal charge, shared electrons are assigned to the more electronegative atom. B. In calculating formal charge, unshared electrons are assigned to the atom on which they are found. C. In general, the Lewis structure in which the atoms bear the lowest formal charges is the preferred one. D. In general, the Lewis structure in which any negative charge resides on the more electronegative element is the preferred one. E. Formal charges do not represent the real charges on atoms. 11. Consider the following molecules which contain carbon-carbon bonds: ethane (C2H6), ethyne (C2H2), benzene (C6H6) and ethene (C2H4). The correct ordering in terms of carbon-carbon bond length is: (Where A>B means the carbon-carbon bond in A is longer than that in B.) A. ethyne> ethene> ethane> benzene B. ethyne> benzene> ethene>ethane C. ethane> benzene> ethene> ethyne 12. Propyne, H–C≡C–CH3, has how many sigma (σ) and how many pi (π) bonds? A. B. C. D. E.

8 σ, 0 π 5 σ, 1 π 5 σ, 3 π 3 σ, 2 π 6 σ, 2 π

13. What is the molecular geometry of SF4? A. B. C. D. E.

seesaw (irregular tetrahedron) regular tetrahedron square pyramid square planar T-shape

14. In what situation is the molecular shape the same as the shape of the electron-domain arrangement? A. B. C. D.

When the central atom does not obey the octet rule When the central atom does obey the octet rule When all of the electron pairs on the central atom are involved in bonding When all but one of the electron pairs on the central atom are involved in bonding E. More than one of the above are correct.

15. How many equivalent resonance structures (having the minimum number of formal charges) are possible for the ion (SFO3)− ? (The central atom is S.) A. B. C. D. E.

1 2 3 4 5

16. What is the orbital hybridization assigned to the two C atoms and the O atom in the molecule below, in order from left to right? H2C=C=O ? A. B. C. D. E.

sp2, sp, sp3 sp3, sp, sp2 sp2, sp2, sp2 sp, sp, sp2 sp2, sp, sp2

17. Using bond enthalpies (given as Average Bond Energies in the Data Sheet) estimate the enthalpy change(ΔH, heat of reaction) for the following gas-phase reaction. (The bond energy value for S−C is 259 kJ mol-1 and that for S−H is 339 kJ mol-1.) HS CH2CH2 SH + 2HF F CH2CH2 F + 2 HSH. A. B. C. D. E.

+824 kJ mol–1 0 kJ mol–1 –824 kJ mol–1 –160 kJ mol–1 +160 kJ mol–1

18. Consider the following three molecules. Which molecule(s) is(are) polar? (That is, which molecules have a non-zero net molecular dipole moment μ?) BF3 NF3 CF4

A. B. C. D. E.

BF3 only NF3 only CF4 only both BF3 and NF3 none of them

19. Which of the following statements is INCORRECT? A. The bonding in a linear arrangement of electron domains can often be rationalized using sp hybrid orbitals. B. When assigning the orbita C. In the molecule H2C=O the H−C−O bond angles are slightly greater than 120°. D. Double bonds take up more space than single bonds. E. In NF3 there are bond angles that are slightly less than the regular tetrahedral angle of 109.5°.

22. Which property is NOT a characteristic of most ionic liquids? A. B. C. D. E.

Non-volatile Non-flammable Orderedphaseabovethemeltingpoint Mismatch of size/shape of anion and cation Polyatomiccationsandanions

24. Which ONE of the following pairs of molecule and intermolecular force is CORRECT? A. B. C. D. E.

Ethene (C2H4), dipole-dipole. H2S,onlyLondondispersion CH3CH2NH2,hydrogenbonding NCl3,onlyLondondispersion MgBr2,dipole-dipole

25. Tungsten (W) has the highest melting point of all the pure metals (3422 °C). Using your knowledge of metallic bonding, choose the best explanation for this fact from the selection below. A. Tungsten has electrons in the 5d subshell. B. Tungsten’s molecular orbitals form a continuous band. C. Tungsten has a half-filled s-d molecular orbital band, so the bonding between atoms is of maximum strength. D. Tungsten has as many anti-bonding electrons as bonding electrons, so the bonding between atoms is of maximum strength. E. Tungsten has a large first ionization energy, so it will not form an ionic lattice....