Name: 1: /33 Grade: /100 2: /33 3: /33 +1 free point. Midterm Exam II. CHEM 181: Introduction to Chemical Principles October 9, 2012

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1 Name: 1: /33 Grade: /100 2: /33 3: /33 +1 free point Directions: Do all three problems. Midterm Exam II HEM 181: Introduction to hemical Principles ctober 9, 2012 Show all of your work neatly and clearly. Do not skip steps. Partial credit will be awarded for all problems. orrect answers will not receive credit if your work is not shown. If you are not sure exactly what a question means, ask! Not all problems are of equal difficulty, but all are worth the same fraction of the overall grade. 1

2 1. Shown above are IR spectra for acetone and deuterated acetone. (a) Identify each of the starred features in the top spectrum as H stretches = stretch stretches H bends/scissors/wags bends (b) For each transition marked in the top spectrum, mark the analogous transitions ( D, =, and stretches, and D and bends) in the bottom spectrum. 2

3 2. The 1 H NMR spectra on this page and the next are all of compounds with the molecular formula 4 H 8 2 : 3

4 4

5 hoose from the compounds below (H atoms not drawn) and assign one structure to each spectrum. 5

6 3. omplete the following equilibrium problems: (a) The equilibrium constants for the following reactions are given below: N 2 (g) + 3H 2 (g) 2 NH 3 (g) atm (g) + 2 (g) N 2 (g) atm 1/2 alculate the equilibrium constant for the reaction NH 3 (g) + 2 (g) N 2 (g) H 2(g) (b) The equilibrium constant for the equation 2Il(g) I 2 (g) + l 2 (g) is K c = alculate the equilibrium concentrations of Il(g), I 2 (g), and l 2 (g) when 0.65 moles of I 2 (g) and 0.33 moles of l 2 (g) are mixed in a 1.5 L reaction vessel. 6

7 (c) The equilibrium constant for the reaction NH 4 HS(s) NH 3 (g) + H 2 S(g) is K c = M 2 at 25. Follow these steps 10 g of NH 4 HS(s) is placed in an evacuated 1 L reaction vessel, the above reaction is allowed to run until equilibrium, an additional 0.01 moles of NH 3 (g) is added to the container, and equilibrium is once again established. What will the final concentrations of NH 3 (g) and H 2 S(g) be? 7

8 Infrared Absorptions for Some Functional Groups compound absorption (cm 1 ) assignment alkanes H stretch H H bend alkenes H stretch = stretch alkynes H stretch stretch aromatic rings H stretch symmetric ring stretch asymmetric ring stretch alcohols H stretch (usually v. broad) carboxylic acids H stretch (v. broad) = stretch aldehydes, ketones = stretch esters, ethers stretch amines H stretch(es) NH bend nitriles N stretch alkyl halides l stretch Br stretch Vibrational frequency: Reduced mass: ν = k m µ = m 1m 2 m 1 + m 2 8

9 Some 1 H NMR hemical Shifts proton environment chemical shift, ppm H 0.2 R H R H 2 R 1.3 R' R R'' H 1.5 =H H 2 3 aromatic H aromatic H = H HF Hl 3 4 HBr HI 2 4 R R' H R R' H H R' H H H = R H 9 10 R H aromatic H RNH R H 9

10 For a chemical reaction the equilibrium constant expressions are K is also written as K. aa + bb c + dd K = []c [D] d [A] a [B] b and K P = P c P d D P a A P b B Quadratic formula for the solution is ax 2 + bx + c = 0 x = b ± b 2 4ac 2a 10

11 The Periodic Table of the Elements 1 H Hydrogen He Helium Li Lithium Be Beryllium B Boron arbon N Nitrogen xygen F Fluorine Ne Neon Na Sodium Mg Magnesium Al Aluminum Si Silicon P Phosphorus S Sulfur l hlorine Ar Argon K Potassium a alcium Sc Scandium Ti Titanium V Vanadium r hromium Mn Manganese Fe Iron o obalt Ni Nickel u opper Zn Zinc Ga Gallium Ge Germanium As Arsenic Se Selenium Br Bromine Kr Krypton Rb Rubidium Sr Strontium Y Yttrium Zr Zirconium Nb Niobium Mo Molybdenum Tc Technetium (98) 44 Ru Ruthenium Rh Rhodium Pd Palladium Ag Silver d admium In Indium Sn Tin Sb Antimony Te Tellurium I Iodine Xe Xenon s esium Ba Barium La Lanthanum Hf Hafnium Ta Tantalum W Tungsten Re Rhenium s smium Ir Iridium Pt Platinum Au Gold Hg Mercury Tl Thallium Pb Lead Bi Bismuth Po Polonium (209) 85 At Astatine (210) 86 Rn Radon (222) 87 Fr Francium (223) 88 Ra Radium (226) 89 Ac Actinium (227) 104 Rf Rutherfordium (261) 105 Db Dubnium (262) 106 Sg Seaborgium (263) 107 Bh Bohrium (262) 108 Hs Hassium (265) 109 Mt Meitnerium (266) 110 (269) 111 (272) 112 (277) e erium Pr Praseodymium Nd Neodymium Pm Promethium (145) 62 Sm Samarium Eu Europium Gd Gadolinium Tb Terbium Dy Dysprosium Ho Holmium Er Erbium Tm Thulium Yb Ytterbium Lu Lutetium Th Thorium Pa Protactinium U Uranium Np Neptunium (237) 94 Pu Plutonium (244) 95 Am Americium (243) 96 m urium (247) 97 Bk Berkelium (247) 98 f alifornium (251) 99 Es Einsteinium (252) 100 Fm Fermium (257) 101 Md Mendelevium (258) 102 No Nobelium (259) 103 Lr Lawrencium (262) 1995 IUPA masses and Approved Names from masses for from &EN, March 13, 1995, p from