Exam1_Sln_2008 - .r 3‘73 flak-T“ W11 I U N I V E R SIT...

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Unformatted text preview: -.-,.r 3‘73!!! flak-T“; W11 I _- U N I V E R SIT Y 0 F COLLEGE OF ARTS AND SCIENCE ROCHES' I 13R DEPARTMENT OF CHEMISTRY Chemistry 131 — Preliminary Exam I 2 October 2008 8:00 am. to 9:30 am. Name: jOi/“fl ID #: 00 7g Workshop Meeting Time (day/hour and building) MTV/RF I I; 00 10/14 (2 pts. Extra credit) This exam consists of six (6) questions, one extra credit problem, and a page of potentially useful information. Please check BEFORE you begin to make sure that you have a complete exam. Please do all your work on the pages provided. You may use the backside of pages for additional work, but please tell us that you are doing so (i.e. an arrow with a note in clear English saying "more work on back"). SHOW ALL WORK. GIVE UNITS for all answers that require them. Partial credit can only be given for those answers for which work is provided. CIRCLE YOUR ANSWER. We ask this so that we don't have to interpret what you intended as your final answer. GOOD LUCK! Prob. w.s. 1(30) 2(25) 3(30) 4(20) 5(35) 6(25) E.C.(5) Total MS— Score University of Rochester Rochester. New York l4627-02l6 lmo\ 1) Note: these problems can be solved with little calculation. Showing work is not required. Consider the following four samples: L:+l I ”l ”W A/ 01 1 mol of Lithium Hydride 64.05 g of Ammonium Nitrite H110 W1. é 18.02 g of Dihydrogen Monoxide 2.0 mol of Dinitrogen tetr xide a) (5 pts.) Write the molecular formula for the sample that has the most hydrogen atoms. A/Ht‘ A/OL b) (5 pts.) Write the molecular formula for the sample that has the least a_t9_m. L; H c) (5 pts.) Write the molecular formula for the sample that has the most molecules. NLOLI 1d) Consider the following four solutions: 944ml 05 Mal 0.75m0) 2.0\L 0f1.\0 M NaCN 1.0 L Of 0.5 M K2304 0.5 L of 1.5 M KC103 m0 2.0 L of 0.5 M K2803 (5 pts.) Write the chemical name in the space below for the sample that has the most total number of ions. godlium Cyaoldbe (5 pts.) Write the chemical name in the space below for the sample that has the highest concentration of cations. Pomsm Ch lo rode (5 pts.) Write the chemical name in the space below for the sample that contains the most oxygen atoms. QO+QSS sum SOL] ‘P \‘l‘C V2, Cteélxt moor “SH “WW/ah ‘12, meld 90V VS“ flame 2) a) (5 pts) In 1996, the Nobel Prize in Physics was given for the discov 3 He. How many protons, neutrons, and electrons are in 3 He? 21 Pt‘inASx 31 eledrom) l hadron b) (5 pts) Tritium, 3 H is a radioactive element that emits electrons and has been used in self- powered lighting applications — like watches. How many protons, neutrons, a . ‘ ‘ - e - are in H9 l profoni ) leledi‘on) <1 081550005 c) (5 pts) Which is heavier 3He or 3H and by how many g? (neglect any electron mass) 3 H ‘ bHc :(a medians 1—l Profon) —~ (l nc‘xfrm + 2 (”073/6 l new-iron P- lfflb’r’vx ~__ l~00$645mm — [.007477qmu :— LW 70‘ max £4404» V53"; : Ch . GXKK d) (5 pts) What is the mass‘b;~ 8,000,000 (ie. 8 million) methane molecules? (Methane = CH4) (5.0'/DAMleLuLlej Kim), K (waft/Hawk A 0;,1'/0”5;alem/a ma ” Duly ’— e) (5 pts) The ratio of oxygen to carbon by mass in carbon monoxide is 1332100. Find the formula of an oxide of carbon in which the ratio by mass of oxygen to carbon is 2.00: 1 .00. CO has maésoflfj;% Al WW5 C Wm+ Masso .. 3.:i 3?. / "‘ l 3 WfifiC. 3) Equilin is an estrogen from horses, and is being used for hormone replacement therapy in people (nice). Equilin contains only carbon, hydrogen and oxygen. Combustion of a 13.42 g \ sample of Equilin (i.e. with excess oxygen) produced 39.61 g C02 and 9.01 g H20. a) (5 pts) How many mol of carbon and how many mol of hydrogen are in the 13. 42g sample 0 Equilin? ‘7 6 1 Mel .- 00 CO lmol C 3 [3% X06. 00xL+ llblb(0v~ O 9 mOl 1x“ C01 0 lm l :1 (D QJhol‘H q‘olj H7, X(;¢1fooz+lé-OD)3H19 O 500ml “1 Km“ 147,5 :— b) (gpts) How many g of oxygen are in the 13.42 g sample of Equ' '- OtclOO mol C x [2‘0];>1 : /0.<go73 C QJB W o Locomol H >< 103% , boars H c) (wpts) What is the empirical formula for Equilin? (“01 O 3 [$0.330 K lmolo: Formulq CS OCO.:> H(OO.IOOD. IAH/l Cm H ‘7710 d) (5 pts) The molar mass of equilin is 268.34 g/mol. Find the molecular formula for equilin. $3 [mass O'F 67H1001 1 CHlLGDT /a([100?)f—/61001 1311.17 g6 mass 3? thL‘DO'le’o-24813y 12> MO/ECoc/OLF 'FOFWILC)q 4) Suppose that you were taking an inorganic chemistry lab where you had to measure the mass spectrum of Ge. You were distracted by the latest hot You Tube video and realized too late that your mass spectrometer jammed — both on the beginning and end of your run. Thus, the spectrum you obtain below may or may not be incomplete. In other words, you may be missing one isotope — either at the front or back end of your plot. Relative Abundance (i.e. detector counts) 71.9217 72.9234 73.9219 75.9219 Mass (amu) a) (15 pts) Using the data from just the mass spectrum shown above, determine the' 'apparent" atomic weight of Ge. Note: The y axis units are NOT exp11c1tly percent ;abundance",[email protected] 3:7.)(73 7m); + —5—:~%>Q5.72 W95 Ga: Héé ,_ l5? " \ +u/0 b) (5 pts) Is an isotope missing? If no state in one sentenceSwhy not. If yes, state in one sentence why you conclude it is missing and state at which end of the plot (i e. beginning or end) the isotope should appear : 72‘ 51 YC§ Fliom Pefxcfiakc jab/e/ mass (5—1: (moi a 96—4: WLMDL\ ‘5 1&5 Than Wail ‘l’hz M6155 \Spcc‘i‘fum [m‘pl' HJQZG An 507va Q)‘\5 “mg/E M6533 1W?“ Tb; bea'am'zlj “gilt/“en 0? Tina? ‘3 oi‘ /57.4 I j/mol 54/0 rj/w' 5) Consider the reaction of aqueous Copper Sulfate with aqueous Potassium Hydroxide. If you mixed a 500 mL of a 0.1 M Copper Sulfate solution with 250 mL of a 0.2 M Potassium Hydroxide solution you would see a blue precipitate, which 18 solid Copper droxide. L7 7 3/144) l 2’a) (5 pts) Write a balanced complete lonic equation for this reaction 7 gem Sowéfl + 1*? airman —% 040*“ “3 til/(“N 56167! . K J 1% b) (5 pts) Wr1te a balanced net ionic equation for this reaction. $ +QS + ‘n P Q (Grubs) 1/ 7%" (”(9 +913: o‘clfi‘n‘ol K (éZSFQéoofifioOfll <3 QLOHL: may 7‘22 J55 935 d) (5 pts) What is the final concentration of potassium ions in solution? 133+): “Ml K+ .- m0\ OH“, 0105‘ __ d.Oé7/V\ f, +07% volume 09500 _: LK’j we» ® e) (5 pts) What IS the final concentration of copper ions in solution?_2’ Mal Q3“ (LH-ox/er: 0.05—Imlcut lmol OH-flo O‘O‘Sml O‘H— ~50 X ,- Cl/L\(O 053-— ” 01 Gag-Ni Cot; \ Mo\ Cu” >< {La-I‘m ’22!“ A . O‘ngo.09\§:,o.02§mal C.L he‘dvqr‘ 1'6 9T5 rfial“ Rad/+64 LT— 9L4373/0/me 5‘1. 7 6) A mixture of solid metallic Al and MnO re ct at high temperatures to produce solids Mn )1 metal and A102. 34‘ 3 M1 5838’ a) (5 pts) Write a balanced chemical equation for this reaction. A! (57 + New ———> Macs) + Prl as} b) (15 pts) The mixture of the two reactants is 67.2 % by mole Al. Starting with 250.0 g of the reactant mixture, what is the theoretical yield of Mn in grams? TWO %uqfi‘oq§ [A TWO MKS (D 21503 : (amflmi A\)+(%.<717)(W,\ Mao.) Lo? No\ (H 7X moi Mnob: c) (5 pts) If the actual yield for this reaction was 43.2 g, what would be the percent yield? thaw i er $23 m Extra Credit Problem (5 pts) (warning — do only after you have completed the exam — these are generally hard and the payoff is small) A 2.25 g sample of scandium metal is reacted with excess HCl to produce 0.1502 g of hydrogen gas. What is the chemical formula of the scandium chloride that is produced in the reaction? 15 ofim‘Hf/‘gax Hwfi ‘3 ‘ '« ‘ " Sag/ngfl oval Sc: 3ng 112;: @ (223) Potentially Useful Information Avogadro’s Number, N = 6.02214 x 1023 mol'l e/m = -1/7588 x 10H C/kg 2X where X = element symbol, A = mass number, Z = charge number Average atomic mass = 2 aiMi ; where ai is the abundance of isotope i having mass Mi Metals tend to lose electrons to become cations, M+,M2+, etc Halides tend to gain electrons to become anions, X' The mass of N atoms equals the atomic mass in grams Mass of '3 C = 13.003355 amu Number of moles = sample mass/molecular mass 1 amu = 1.6606 x 10'24 g Mass of proton = 1.007277 amu mass of neutron = 1.008665 amu number of moles of atom X = [sample mass (g)/molecular mass (g/mol)][# mol of X/mol of molecules] M = molarity = moles of solute/liters of solution Mass l3C/mass 12C = 1.0836129 10 81 12C 01 14N 01 16 00 13 15 16 Al Si 26.98 28.09 30P 97 32S 06 22 26 27 29 30 32 Ti Fe Co Cu Zn Ge 44. 96 47 88 . 55.85 58.93 58M. 69 63. 55 65. 38 . 72.59 74.92 78.96 40 42 43 44 45 46 47 48 51 52 Zr Mo Tc Pd Ag Cd 88 91 91. 22 92N.91 95,94 (98) . . 106.4 107.9 112.4 . . . . 72 74 75 78 79 80 Hf W Re P1 Au Hg ' 138. 9 178. 5 . 183.9 186.2 . . 195.1 197.0 200.6 . . . 89 Ac 58 59 60 64 65 Ce Pr Nd Gd Tb 140.1 140.9 144.2 ( . . 157.3 158.9 91 92 94 95 96 97 Bk 247 251 226 (227) 90 Th 3 U m 232.0 (231) 238.0 ( (244) (243) (247) ...
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