CHEM 107 (Spring-2005) Exam 3 (100 pts)

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1 CHEM 107 (Spring-2005) Exam 3 (100 pts) Name: , Clid # LAST NAME, First (Circle the alphabet segment of your LAST NAME): A, B C-G H-N O-S T-Z Please answer the following questions: Part I: Multiple Choices (56 pts: 4 pts each + 4 pts bonus). Circle the ONE best answer: 1. Which set of temperature and pressure conditions will cause a gas to exhibit the greatest deviation from the ideal behavior? a) 100 ºC and 4 atm b) 100 ºC and 2 atm c) -100 ºC and 4 atm d) 0 ºC and 4 atm 2. How many molecules of hydrogen sulfide, H 2 S are contained in 2.00 L of H 2 S at 1 atm and 27 C? a) 5.37 x b) 1.20 x c) 4.89 x d) 8.12 x What volume of hydrogen at STP can be produced by reacting 8.30 mol of Al with sulfuric acid, H 2 SO 4 according to the equation: 2 Al (s) + 3 H 2 SO 4 (aq) Al 2 (SO 4 ) 3 (aq) + 3 H 2 (g) a) 279 L b) 140 L c) 186 L d) 93 L 4. Consider four identical 1.0 L flasks containing the following gases each at 25 C and 1 atm pressure. For which gas do the molecules have the lowest average velocity? a) SO 2 b) O 2 c) H 2 d) same for all 5. Assuming ideal gas behavior. Which of the following statements is INCORRECT? a) The pressure of the gas results from the collisions of the gas molecules with the wall of the container. b) The volume occupied by a gas depends on its temperature, pressure and number of moles. c) When the temperature of a gas sample is increased at constant pressure, the density of the gas will decrease. d) In a mixture containing O 2 and N 2 molecules, the O 2 molecules, on the average are moving faster than the N 2 molecules. 6. What do these have in common? 20 Ne 19 F - 24 Mg 2+ a) the same number of protons b) the same number of neutrons c) the same number of electrons d) the same size 1

2 7. The number of unpaired electrons in a gaseous arsenic atom, As is a) 2 b) 3 c) 5 d) 0 8. Which pair of particles has the same number of electrons? a) F, Mg 2+ b) Ne, Ar c) Sr +2, Se 2- d) Al 3+, P 3-9. Which of the following is paramagnetic with three unpaired electrons? a) Y b) Al c) Co 2+ d) P Which set of quantum numbers is correct and consistent with n = 4? a) l = 3 m l = -3 m s = + ½ b) l = 4 m l = +2 m s = - ½ c) l = 2 m l = +3 m s = + ½ d) l = 3 m l = -3 m s = The wavelength of a photon is largest in the case a) X-rays b) ultraviolet c) visible light d) infrared 12. Which of the following species does not obey the octet rule? a) CO 2 b) NF 3 c) BF 3 d) OF How many electron pairs are there around the central atom in the Lewis structure of XeF 4? a) 2 b) 3 c) 4 d) Which element has the greatest 1 st ionization energy ionization energy? a) As b) Ge c) Se d) Kr 15. Which of the following is the ground state electron configuration of Cu +? a) [Ar] 4s 2 3d 10 b) [Ar] 4s 2 3d 9 c) [Ar] 4s 2 3d 8 d) [Ar] 3d 10 2

3 Part II. Bonding (14 pts): 1. Draw the Lewis structure for the nitrite ion, NO - 2, draw the resonance structures, if there is any then: predict: a) number σ and π bonds d) The molecular hape of the ion Lewis Structure & resonance structures (if any) a) Molecular shape: b) # of σ bonds and # of π bonds Part III. Calculations (30 pts: 10 pts each) Show all work for full credit. Please express all answers with the proper units and correct number of significant figures. 1. An important chemical reaction in the manufacture of Portland cement is the higher temperature decomposition of calcium carbonate to give calcium oxide and carbon dioxide CaCO 3 (s) CaO (s) + CO 2 (g) Suppose a 1.25 g of CaCO 3 is decomposed by heating. How many milliters of CO 2 gas will be evolved, if it will be measured at 740 torr and 25ºC? Volume of CO ml 3

4 2. a) Calculate to four significant figures, the wavelength in nanometers in the H-atom spectrum that arises from the electron transition of n = 4 to n = 2. b) In what spectral region does this transition occur? c) Is energy absorbed or emitted? a) Wavelength (nm) nm c) Spectral region: b) 3. A sample of oxygen is collected over water at 20º C and a pressure of 738 torr (the vapor pressure of water at this temperature = 17.5 torr). Its volume is 310 ml. a) what is the partial pressure of the oxygen? b) What would be its volume when dry at STP? a) P O2 = 720 torr b) V = 274 ml 4

5 PREFERENCE SHEET FOR CHEM 107 Exam 3 Spring 2005 You will have 55 minutes to complete this exam. The exam has 4 pages plus the Periodic Table & Reference page. When you are told to do so, tear off the Periodic Table cover sheet and use as required during the exam. Equations and Constants: Density (d) = mass/volume PV = nrt K.E. = ½ mv 2 Average speed of a gas, u = (3RT/M) 1/2 (Rate of effusion of B/Rate of effusion of A) = (M A /M B ) 1/2 ν = R H /h [1/(n lo ) 2 1/(n hi ) 2 ] E = h ν c = λ ν R H = x J h = x J.s c = 3.00 x 10 8 m/s Avogadro s Number = x R = L.atm/mol.K 1 atm = 760 torr = 760 mmhg At STP 1 mol of a gas = L General Solubility Guidelines All nitrates are soluble. All salts of sodium, potassium and ammonium are soluble. All chlorides, bromides and iodides are soluble except Ag + 2+,, Hg 2 and Pb 2+. All sulfates are soluble except Ba 2+, Sr 2+, Pb 2+ and Hg All acetates, chlorates and perchlorates are soluble. Everything else will be considered insoluble H Li Na K Rb Cs Fr (223) 4 Be Mg Ca Sr Ba Ra Periodic Table of the Elements Sc Ti V Cr Y La Ac Zr Hf Rf (261) 41 Nb Ta Db (262) 42 Mo W Sg (263) Mn Tc (98) 75 Re Bh (262) 26 Fe Ru Os Hs (265) Co Ni Cu Zn Rh Ir Mt (266) 46 Pd Pt Uun (269) 47 Ag Au Cd Hg UuuUub (272) (277) B C N O F Al Ga In Tl Si Ge Sn Pb P As Sb Bi S Se Te Po (209) 17 Cl Br I At (210) 2 He Ne Ar Kr Xe Rn (222) Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er (145) Th Pa U Np Pu (244) Am (243) CmBk (247) (247) 98 Cf (251) 99 Es (252) 100 Fm (257) Tm Md (258) 70 Yb No (259) 71 Lu Lr (260) 5

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