Hour Exam I Name: Fall 2011

Transcription

1 PLEASE EAD: This practice exam is based on last year s Chem 22 exam #1. I have highlighted those questions that I will not ask you on this exam (but you should definitely try to do them on your own), but instead, I will have 2-3 questions from the Fundamental Sections that deals with stoichiometric type calculations (i.e. limiting reagent, empirical/molecular formula, % yield, molarity, etc.) *Make sure you download the hint page (located on the Exam Info page of our course website) to help you work on the practice exam Chem 22 Hour Exam I, Oct Prof. Gruebele Instruction Page Instructions: Name: Signature: Quiz Sect: TA: Do not open this booklet or begin the exam until you are told to do so; in the meantime, fill in the information requested below. This midterm contains 25 multiple-choice questions (4 pts. each). Fill in your name, signature, quiz section and TA name above. On the bubble answer sheet fill in the same information; use the two digits of your quiz section under "class" (e.g. section AQ4 ). Failure to fill in all information may delay grading of your exam. With your signature, you pledge that the answers you provide are obtained with no aid but this exam booklet and a calculator. You may write on any part of the exam. However, only bubbles filled in on the answer sheet will count for credit. The exam booklet will be returned to you during quiz section; circle your answers on it if you want a personal record (bubble sheets will NOT be returned). Exam time: 1 hour; there are 4 pages of questions. Times will be noted on the board. efer to the hint sheet for any equations or numbers not given in the questions that you might need. 1

2 1) An electron in a plasma TV display screen is moving freely at a velocity of 5 m/s. What is its kinetic energy in Joules? a) b) c) d) e) Who says beans don t have an immune system? Identify the numbered hybridized atoms in wyerone acid, which beans use to kill attacking fungus. 2) a) sp b) sp 2 c) sp 3 3) a) sp b) sp 2 c) sp 3 4) a) sp b) sp 2 c) sp 3 5) The degeneracy of the first excited state of a particle in a cubic box of either one, two or three dimensions is: [Hint: cubic means all lengths L are equal.] a) 1, 2, 3 b) 1, 1, 1 c),, d) 1, 2, 2 e) 3, 3, 3 6) What is the longest wavelength of a photon that will still ionize a Lithium atom? a) 15.7 nm b) 157 nm c).4 m d) 23 nm e) 4 nm 7) Which of the following is the x-p plot for the lowest energy state of a spring allowed by the Heisenberg principle? 8) The Balmer series of a hydrogen atom is a series of sharp emission lines that ends in the n=2 state. The longest wavelength line is called Balmer-α. What color is this line? [Hint: emitted color is the same as absorbed color.] a) UV b) blue-green c) yellow d) red e) I=infrared 2

3 9) What is the effective nuclear charge of magnesium and, given the IP (same as IE) of similar atoms on the hint page, what is its ionization potential (energy) in kj/mole? a) 1, 942 b) 1.5, 738 c) 1.5, 942 d) 2, 738 e) 2, 942 1) A 4p orbital (n=4, l=1) has how many nodes? (planar = angular is a flat node, radial is a spherical node) a) 1 radial, 2 planar b) 3 radial, 1 planar c) 1 radial, 1 planar d) 2 radial e) 2 radial, 1 planar 11) What is the valence e - configuration of iron, the most stable nucleus in the universe? a) 4s 2 3d 7 b) 4s 1 3d 7 c) 4s 2 3d 6 d) 3s 2 3d 7 e) 3s 1 3d 7 12) Two methyl radicals are coming together to make a chemical bond and form ethane. The potential energy as a function of the C to C bond distance looks like. a) b) c) d) 13) Based on electronegativities, which of the following uncharged molecules has incorrectly assigned partial charge(s) δ? δ + /2 6δ + a) δ- H δ - δ + /2 O δ + /2 F b) O=S=O c) δ + δ - δ - F δ - δ - I-Br d) F-S-F e) a and d H δ - F δ + δ /2 - Fδ - 3

4 14) Using MO theory, the bond order and magnetism of the charged molecule ArH +, common in the upper atmosphere of the Earth, is a) 1, paramagnetic b).5, diamagnetic c).5, paramagnetic d) 1, diamagnetic e) 1.5, paramagnetic 15) When you fill electrons into the MO diagram of the N 2 molecule, the lowest unoccupied MO looks like: a) b) c) d) e) 16) Ozone is a dangerous pollutant at low altitude, but an important UV screen in the upper atmosphere. Which Lewis dot structure is closest to the actual wavefunction of Ozone? 17) Phosphene (PH 3 ) is a toxic gas used in the manufacture of n-doped semiconductors chips. All H-P-H bond angles are 93. To a first approximation, which atomic/hybrid orbitals on phosphorous best describe the bonding in the localized electron picture? 18) Two electrons fill into energy levels as shown to make the lowest energy state. Which of the following is definitely true: a) This must be an excited state, could never be the lowest state b) This is close to the lowest energy state, but the upper e - should be flipped 4

5 c) If E is small, Pauli exclusion minimizes e - repulsion, making it the lowest state d) This violates the Pauli exclusion principle because both e - have the same spin e) If E is large, the upper e - should be moved down without flipping. 19) What is the electron affinity of O + atomic ion? a) 142 b) 1314 c) 1682 d) The same as O atom e) insufficient information on hint page 2) p x ~ sinθ cosφ. p y ~ sinθ sinφ. p z ~ cos θ. An electron is in the triply degenerate p state, nothing further specified. The probability P(θ, φ) of finding the electron at angles θ and φ is a) sinθ (sinφ + cosφ) b) independent of φ c) independent of θ and φ d) independent of θ e) sin 2 θ sinφ cosφ 21) A single potassium atom is inside the cavity of a C 6 molecule (cavity diameter 7 Å) in the lowest possible energy state. What is the velocity spread? a) b) 15 m/s c) 15 m/s d) ª 1 15 c e) K does not fit inside a C 6 cavity 22) Which particle has greater momentum? a) An electron moving at 5 m/s b) An X-ray photon of.5 nm wavelength 23) The molecule trans-hexatriene = acts as a box for electrons because of the conjugated pi electrons. Assuming the particle in a box model for the pi electrons, and knowing the lowest energy photon that can be absorbed has frequency Hz, you estimate the size of the hexatriene box to be: a) < 2 Å b) 2 to 4 Å c) 4 to 6 Å d) 6 to 8 Å e) >8 Å 5

6 24) Which of the following orbitals do not have the right symmetry to make a bonding or antibonding combination when the orbitals are brought together along the dotted line? a) b) c) d) e) 25) 1) x 2) x 3) x Which wavefunction above best matches the orbital formula ~ (2-r/a) e -r/a? a) 4, 2s b) 2, 1s c) 5, 2s d) 3, 3p x e) 1, 3p x 4) x 5) x That s it, folks! 6