Your full name (PLEASE PRINT) Third hour test page 1 of 5 November 9, 2006 Your scheduled Tuesday quiz section (please circle) B hr E hr

Transcription

1 EM 111 Your full name (PLEASE PRINT) Third hour test page 1 of 5 November 9, 2006 Your scheduled Tuesday quiz section (please circle) B hr E hr 1 Your scheduled Tuesday quiz instructor: Make sure your test has FIVE pages---notify us immediately if it does not. Do NOT detach pages from the staple. You may use a writing implement, hand-calculator, the pink data page, and your Periodic Table (unmarked, honor code) as obtained in this course. NO scratch paper is permitted! As requested of the faculty by the Student Executive ommittee, students must sit in every other seat during the test. The PROPER METOD (i.e., Problem Set 0) must be shown clearly on all problems, and final answers must be expressed in appropriate form. Pay attention to dimensions!! When blanks for answers are provided, write your answer to be graded in the blank---we may not grade answers written in other locations! For the purposes of this test, represent hydronium ion as 3 O + and not as + (aq). It is your responsibility to make sure the test you turn in has 5 securely fastened pages.

2 1. (7 pts) If an electron has an uncertainty in velocity of 5.0 x 10 5 cm/s, what is the minimum uncertainty in its position? Fundamental Equation(s): 2 Answer: 2. (7 pts) alculate the energy in kj/mol for radiofrequency photons of 91.5 Mz. Fundamental Equation(s): Answer: 3. (7 pts) In a molecule of 3 - N:, what orbitals (be explicit) are overlapped to form each of the following bonds, using valence bond theory: [Be sure to distinguish between AO's, MO's, and O's in your answers.] between (left) and sigma-bond between (left) and (middle) a pi-bond between (right) and N. In what orbital is the N lone pair? 4. (9 pts) (a) Draw the three resonance structures (where each atom has an octet) of N 2 O in the boxes. Write the formal charge on each atom in the blanks below the box. N N O N N O N N O (b) Based on formal charges and electronegativity, circle above which resonance structure is the most reasonable. (c) What is the oxidation number of the central nitrogen atom in the most reasonable resonance structure?

3 3 6. (6 pts) ircle below the molecule(s) that is (are) polar. Draw each molecule, and then draw a dipole moment vector that indicates the direction of polarity (if there is a net dipole moment)---that is, which is the negative end and which is the positive end of the molecule? If the molecule is not polar, do not draw a vector. (a) BF 2 (b) SO 3 7. (4 pts) What are the orders of the N-O bonds in NO 2 - and NO2 +? The N-O bond in one of these ions is 110 pm and 124 pm in the other. To which ion does the 110 pm bond length correspond? What is the name of the ion NO 2 -? Use the space below for your work. 8. (6 pts) ompare the element Na, Mg, O, and P. Which has the largest atomic radius? Which has the most negative electron affinity? Place the elements in order of increasing ionization energy (lowest to highest). 9. (6 pts) Which has the largest atomic radius, S, Se, or l? Which has the larger radius, Br or Br -? Which should have the largest difference between the first and second ionization energy: Si, Na, P, or Mg? 10. (12 pts) Show by appropriate formula(s) what species are present after each of the following bulk substances are mixed (individually) with water. learly distinguish between ions, molecules, and solids in the final aqueous mixtures. 2 Se Mn 2 O 3 NO 3 Ni(O) 2 N 4 OAc [r(n 3 ) 6 ][lo 4 ] (6 pts) Translate these given data into the style of bracketed formulas as in P.S. 70 (expressing the concentrations of ultimate species present in aqueous solution): 0.2 M 2 SO M F 0.1 M KO

4 4 12. (10 pts) (a) Draw a molecular orbital energy correlation diagram below for N 2 in the manner done IN LASS in your notes (not the book way). (b) arefully label both the atomic and molecular orbitals in your diagram. Orbital cartoons are NOT required in your diagram. (c) Fill your diagram with the appropriate number of electrons for N 2. (d) What is the bond order of N 2? (e) What is the bond order of N 2 +? (f) Is N 2 paramagnetic? (g) Would N 2 + be stable by itself? (h) Is N 2 2- paramagnetic? (i) Which would have a higher ionization energy, N atom or N 2? 13. (6 pts) Draw pictures of the following individual orbitals (be sure to indicate phases, axes, and label and identify nodes where appropriate): (a) σ 2p (b) 3d xz (c) sp (2 pts) learly and darkly circle any and all stereogenic centers in the amino acid at right. If no stereogenic centers exist, write none in the blank:. O (10 pts) The Born-aber process is one of the most important industrial processes, because it is the only large-scale means for producing ammonia, critical in agriculture and chemical industry. The Born-aber process is run at high pressure, high temperature, and with an iron metal catalyst. 3 2 (g)+ 2N 2 (g) 2N 3 (g) (a) Write the equilibrium constant, K, using brackets for concentration: (b) ow is the equilibrium shifted (left, right, or no shift) if: N 2 (g) is added the system is compressed unreactive Ar is added without changing the volume 2 is removed more Fe(s) is added Δ is negative and the system is heated LiF(s) is added O N (7 pts) ircle the one best answer for each statement/question below:

5 5 Solvatochromism occurs by: a) the solvent perturbing a dye s MO energy levels. b) the solvent absorbing visible light c) the solvent changing color when exposed to light d) the solvent causing an electron spin flip In G-MS, ions are: (a) separated by the gas chromatograph (b) separated by magnetic or electric fields (c) generated by radiofrequency pulses (d) detected by light emission (e) never generated---only neutral molecules are detected The picture at right represents a pair of a) enantiomers b) diastereomers c) conformers d) constitutional isomers Which of the following DOES NOT support the assertion that odor receptors in your nose are an asymmetric environment? a) many biological receptors are made up of amino acids which have stereogenic centers b) very dilute concentrations of compounds can be detected c) the human nose can detect different odors for s-carvone and r-carvone d) many biological receptors are made up of molecules lacking planes of symmetry UV and visible photons can cause which of the following transitions in molecules? (a) electron spin flip (b) nuclear spin flip (c) molecular vibration (d) promotion of an electron to a higher energy orbital In 13 NMR spectroscopy, why is an applied magnetic field needed? a) to cause the molecules to orient themselves in an ordered fashion within the sample b) to align the tiny magnetic fields of 13 nuclei in one of two possible orientations c) to cause all 13 nuclear spin states to have the same energy d) to generate a 13 paramagnetic effect On the sample 13 NMR spectrum you obtained in lab in Expt. 3, each peak corresponds to a) the time required for a particular flipped 13 nucleus to return to its ground state b) a different type of spinning nucleus, such as 1 versus 13 c) a 13 nucleus in a different region of the applied magnetic field gradient d) a 13 nucleus in a different local magnetic environment 17. (3 pts) Using only the space allocated write two or three concise, accurate, grammatical sentences to explain what Rutherford did and the significance of his discovery: l Br l Br 18. (2 pts) What is the maximum number of hybrid orbitals that boron can form? PLEDGE: