74. An electron is promoted from the π to the π∗ molecular orbital in an O₂ molecule following the absorption of a photon. Compared to the bond length in the non-excited molecule, the O₂ bond length will .
(A) be shorter
(B) be longer
(C) not be affected
(D) be same
(E) None of the above.

70. To form a buffer solution with pH = 9.0, how many moles of NH4Cl should be added to 3.0 L of 0.20 M NH3(aq) at 25ºC? (Kb of ammonia = 1.8 × 10‒5 ; assuming the volume of solution does not change after adding NH4Cl) (A) 0.36 (B) 0.72 (C) 1.08 (D) 3.6 (E) None of the above.

71. Which statement about hydrogen bonding is true? (A) Hydrogen bonding is the intermolecular attractive forces between two hydrogen atoms in solution. (B) The hydrogen bonding capabilities of water molecules cause CH3CH2CH2CH3 to be more soluble in water than CH3OH. (C) Hydrogen bonding of solvent molecules with a solute will not affect the solubility of the solute. (D) Hydrogen bonding interactions between molecules are weaker than the covalent bonds within the molecule. (E) Hydrogen bonding arises from the dipole moment created by the equal sharing of electrons within certain covalent bonds within a molecule.

72. How many effective atoms are there in a body-centered cubic unit cell? (A) 1/2 (B) 1 (C) 2 (D) 3/2 (E) 3

73. Which of the following has a zero dipole moment? (A) NH3 (B) HCN (C) PCl5 (D) SO2 (E) H2O

75. Determine the percent dissociation of a 0.18 M solution of hypochlorous acid, HClO. The Ka for the acid is 3.5 × 10−8 . (A) 4.4 × 10−2 % (B) 3.5 × 10−6 % (C) 6.3 × 10−9 % (D) 4.4 × 10−4 % (E) 7.9 × 10−3 %

76. The solubility of CaSO4 in pure water at 0 oC is 1.14 gram per liter. The value of the solubility product is . (A) 7.01 × 10–5 (B) 8.37 × 10–3 (C) 7.01 × 10–2 (D) 8.37 × 10–5 (E) None of the above.

77. It is desired to determine the concentration of arsenic in a lake sediment sample by means of neutron activation analysis. The nuclide As captures a neutron to form As , which in turn undergoes β decay. The daughter nuclide produces the characteristic γ rays used for the analysis. What is the daughter nuclide? (A) (B) (C) (D) (E)

複選題78. As shown below, compound IV can be prepared from reagents I, II, and III. Which of the following reaction conditions is the most suitable for the preparation of IV? (A) I is slowly added to II, and III is then added to the above mixture. (B) I is slowly added to II, and the resultant mixture is slowly added to III. (C) II is slowly added to I, and III is then added to the above mixture. (D) II is slowly added to I, and the resultant mixture is slowly added to III. (E) I is slowly added to III, and II is then added to the above mixture.

79. The equilibrium constant of a certain reaction was measured at various temperatures to give the plot shown below. What is Δ S o (J/mol∙K ) for the reaction? (R = 8.314 J/mol∙K ) (A) 0.20 (B) 3.0 (C) −50 (D) −8.3 × 103 (E) 33

80. For the reaction N2(g) + 2H2(g) → N2H4(l), if the percent yield for this reaction is 41.0%, what is the actual mass of hydrazine (N2H4) produced when 30.57 g of nitrogen reacts with 4.45 g of hydrogen? (A) 24.00 g (B) 28.60 g (C) 15.00 g (D) 12.00 g (E) 14.60 g