Department of Chemistry. Chemistry 121: Atomic and Molecular Chemistry. Final Examination Wednesday, December 7, 2011 Time: 9:00am 12:00

Size: px

Start display at page:

Download "Department of Chemistry. Chemistry 121: Atomic and Molecular Chemistry. Final Examination Wednesday, December 7, 2011 Time: 9:00am 12:00"

Helen Kelly
5 years ago
Views:

1 Student Name: Student Number: The Irving K. Barber School of Arts and Sciences Department of Chemistry Chemistry 121: Atomic and Molecular Chemistry Professors: Dr. Penny Parkeenvincha & Dr. Rob O Brien Final Examination Wednesday, December 7, 2011 Time: 9:00am 12:00 Instructions: Answer questions in the space provided. You may use the backs of pages for rough work or calculations; however, this material will not be formally marked. Be careful with significant figures and be sure to clearly express final answers using appropriate units and significant figures. This exam contains a total of 17 pages, plus one data sheet. Total Marks: 100 Page 1 of 18

2 Answers 1. Part 1: Multiple choice questions. One mark each. Answers in box provided. 30 marks. 1) Which of the following would be considered a chemical reaction? (A) Ice Melting (B) A log burning (C) Dissolving sugar in coffee (D) Boiling water (E) Superheated coffee foaming over when sugar added 2. 2) When 3.0 L of hydrogen gas (H 2 ) reacts with 1.0 L of nitrogen gas (N 2 ), 2.0 L of gaseous product are formed. All volumes of gases are measured at the same temperature and pressure. What is the formula of the product? (A) N 2 H 6 (B) NH 3 (C) NH 4 (D) NH (E) N 2 H ) Two moles of Neon gas at 20.0 C are heated to 350 C while the volume is kept constant. The density of the gas: (A) Increases (B) Decreases (C) Remains the same (D) Not enough information given 4. 4) For a substance that remains a gas under the conditions listed, deviation from the ideal gas law would be most pronounced at (A) 100 C and 2.0 atm (B) 0 C and 2.0 atm (C) -100 C and 2.0 atm (D) -100 C and 4.0 atm (E) 100 C and 4.0 atm 5. 5) Which of the following atomic symbols is incorrect? (A) C (B) Cl (C) 15 P (D) 19 K (E) N 6. 6) What is the wavelength in nm of radiation with a frequency of 5.75 x Hz? (A) 522 (B) 425 (C) 575 (D) 325 (E) None of these 7. 7) Consider single atoms of the following elements floating free in space. Which would be attracted by a magnet? (A) S (B) He (C) Ca (D) Xe (E) None of these Page 2 of 18

3 Answers 8. Chemistry 121: Atomic and Molecular Chemistry 8) Which one of the following decreases as the strength of the attractive intermolecular forces increases? (A) The heat of vaporization. (B) The normal boiling temperature (C) Deviations from the ideal gas law. (E) The vapor pressure of a liquid. (D) The sublimation temperature 9. 9) Consider the element mercury, atomic number 80, atomic mass g. The nucleus of an atom of mercury-199 contains; (A) 80 protons, 119 neutrons, 80 electrons. (B) 80 protons, 119 neutrons. (C) 80 protons, 119 alpha particles. (E) 80 protons, 120 neutrons (D) 80 protons, 80 neutrons ) For which of the following compounds does 1.0 g represent 2.27 x 10-2 mol? (A) H 2 O (B) CO 2 (C) NH 3 (D) C 2 H 6 (E) none of these ) How many atoms of hydrogen are present in 6.0 g of water? (A) 2.0 x (B) 7.2 x (C) 1.1 x (D) 4.0 x (E) ) Which of the following sets of quantum numbers in the form (n,l,m l,m s ) are not possible? (A) (5,2,3,-½ ) (B) (4,3,-2,+½ ) (C) (6,1,0,+½ ) (D) (2,0,0,-½ ) (E) (7,1,0,-½ ) ) What would the Osmotoic Pressure be for a solution that is 1 M of glucose at a temperature of 298K? (A) 298 torr (B) 49 Torr (C) 24.5 atm (D) 49 atm (E) 24.5 torr ) What would the Osmotoic Pressure be for a solution that is 1 M of NaCl at a temperature of 298K? (A) 298 torr (B) 49 Torr (C) 24.5 atm (D) 49 atm (E) 24.5 torr Page 3 of 18

4 Answers ) Capillary action can be explained by? (A) Cohesion (B) Adhesion (C) Hydrogen Bonding (D) Viscosity (E) London Forces ) Consider four 1-L flasks at STP. Flask A contains NH 3 gas, flask B contains NO 2 gas, flask C contains NF 3 gas, and flask D contains N 2 gas. In which flask do the molecules have the highest average velocity? (A) NH 3 gas (B) NO 2 gas (C) NF 3 gas (D) N 2 gas (E) all are the same ) Which of the following will have the largest atomic radius? (A) Rb (B) Sr (C) Te (D) Xe (E) K ) Which of the following elements would be the easiest to ionize? (A) Mg (B) Cs (C) Na (D) Ca (E) Be ) Which of the following would conduct electricity if dissolved in water? (A) BaCl 2 (B) CO (C) CCl 4 (D) SF 4 (E) SO ) Which of the following frequencies corresponds to light with the longest wavelength? (A) 3.00 x s -1 (B) 4.12 x 10 5 s -1 (C) 8.50 x s -1 (D) 9.12 x s -1 (E) 1.20 x 10 9 s ) In He + the relative energy of the orbitals with a principal Quantum number of 3 would be? (A) 3d<3p<3s (B) 3d>3p>3s (C) 3d>3p<3s (D) 3d=3p=3s (E) 3d<3p>3s ) Which of the following would have the largest second ionization energy (IE 2 )? (A) K (B) Ca (C) Al (D) Sr (E) Ga Page 4 of 18

5 Answers Chemistry 121: Atomic and Molecular Chemistry 23) Which of the following characteristics indicates the presence of weak intermolecular forces in a liquid? (A) low heat of vaporization (C) low vapor pressure (E) none of the above (B) high boiling point (D) a high critical temperature 24) Which of the following substances can form hydrogen bonds with water? (A) H 2 S (B) He (C) H 3 C-NH 2 (D) PH 3 (E) H 3 C-CH ) In which case is the bond polarity incorrect? (A) δ+ H F δ (B) δ+ K O δ (C) δ+ Mg H δ (D) δ+ Cl I δ (E) δ+ Si S δ 26) The Cl Kr Cl bond angle in KrCl 4 is closest to; (A) 90 (B) 109 (C) 120 (D) 150 (E) ) What type of structure does the XeOF 2 molecule have? (A) pyramidal (B) tetrahedral (C) T-shaped (D) trigonal planar (E) octahedral ) Which ion is planar? (A) NH 4 + (B) CO 3 2 (C) SO 3 2 (D) ClO 3 (E) all are planar ) Which of the following compounds has the highest boiling point? (A) F 2 (B) I 2 (C) Br 2 (D) Cl 2 (E) All boiling points are about the same since the compounds are all nonpolar ) When bubbles of gas are released from a bottle of pop when it is opened, this is an example of (A) Charles Law (B) Dalton s Law (C) Henry s Law (D) Avogadro's Law (E) Boyle's Law Page 5 of 18

6 Part 2: Various Problems. Answer all questions in this Section. Answers in space provided. Marks as Indicated. 40 marks. 2.1) Name the following compounds CBr 4 NaCN compound name 2 points KHCO 3 Fe 2 O 3 2.2) Give a chemical formula for each of the following substances. 2 points Substance Dinitrogen tetroxide Chemical Formula Nitrate ion Aluminium Oxide Chromium (III) hydroxide 2 points 2.3) Sulfur has three naturally occurring isotopes. One of these S has a mass of amu and natural abundance of 0.75%. The other two S and S have masses of amu and respectively. Given this, determine the natural abundance of all three isotopes. (Hint: use periodic table) Page 6 of 18

7 2.4) 150 ml of N 2(liquid) is added to a 1.00 L container that is initially originally filled with just air (assume air is a binary mixture of N 2 and O 2 ; with the mole fraction of O 2 = 0.22). The container is sealed immediately after the N 2 is added and then allowed to warm to room temperature. What will the equilibrium pressure in the bottle be if the initial atmospheric pressure was 760 torr and the room temperature remains at 20 C through out? At equilibrium, what will the final mole fraction of N 2 and O 2 be? How many grams of O 2 will there be at equilibrium? The density of N 2(liquid) is g/ml. 5 points 2.5) How many grams of sodium must react with 250 ml H 2 O to produce a solution that is 0.15 M NaOH? (assume a final solution volume of 250 ml.) 2Na (s) + 2H 2 O (l) 2NaOH (aq) + H 2 (g) 3 points Page 7 of 18

8 2.6a) Draw the most probable Lewis structures for N 2 O and NO 2. Indicate all nonzero formal charges and which structure that would be expected to be most stable. 3 points 2.6b) Considering the most probable structure for CO 3-2, indicate the type of hybrid orbitals on the Carbon and Oxygen atoms. Predict the expected bond angles. Indicate the relative length and strength of each bond. Show any resonance hybrids and indicate how they are related to the overall observed structure. 3 points Page 8 of 18

9 2.7) The molar mass of an unknown organic compound composed of C, H, O, and S is known to be between 100 g/mol and 150 g/mol. It is also known to contain 25.8% Sulfur by mass. Combustion of a 1.00 g sample produced 1.06 g of CO 2 and 0.58 g of H 2 O. Determine the molecular formula of this compound. 6 points Page 9 of 18

10 2.8a) Show all of the electrons from a nitrogen atom and show how these are related to the (n, l, M l, M s ) notation. 4 points 2.8b) How would the energy needed to remove an electron from Hydrogen be related to the energy needed to remove an electron from He + and Li points Page 10 of 18

11 2.9) Find the mass of CS 2 required to produce 100 g of S 8 if the reaction presented below proceeds in a 77% yield in the presence of excess disulfur dichloride. (the reaction is unbalanced) CS 2 + S 2 Cl 2 S 8 + CCl 4 4 points Page 11 of 18

12 2.10) For the phase diagram given below, explain what process is represented by each arrow, what phases are represented by each letter and the meaning of points (1) and (2). (Does the substance represented by the diagram expand or shrink during freezing. Explain. 4 points Pressure (atm) A N (1) K L C B (2) M Temperature Region A represents Region B represents Region C represents Point (1) represents Point (2) represents Arrow (K-L) represents Arrow (M-N) represents Arrow (N-K) represents Page 12 of 18

13 Part 3: Additional Problems. Answer 3 of the following 5 questions. CLEARLY indicate which 3 you want marked. Otherwise, the first 3 attempted will be marked. Each question is worth a total of 10 marks. Answers in space provided. 30 marks. 10 points 3.1a) A solid mixture contains only SrCO 3 and BaCO g of this mixture is dissolved in ~ 100 ml of 1.0 M HCl. During the process g of carbon dioxide gas is liberated. Calculate the mass percent of each component in the original solid. 3.1b) If the final solution from part A is quantitatively transferred to a 500 ml volumetric flask and filled to the mark with deionized water. What would the concentration of the Strontium (Sr) be in this final solution? Express your answer in both mg/l and Molarity. Page 13 of 18

14 10 points 3.2) Considering the molecules; NO +, NO - and CN +, CN - and being given the relative molecular orbital energy levels as; σ 1s < σ 1s * < σ 2s < σ 2s * < π 2py = π 2pz < σ 2px < π 2py * = π 2pz * < σ 2px * 3.2a) Draw the molecular orbital energy diagram for each molecule 3.2b) calculate the bond order for each 3.2c) indicate the relative bond length and strength 3.2d) indicate paramagnetic or diamagnetic properties Page 14 of 18

15 10 points 3.3a) Ozone, O 3, acts as a filter of harmful UV radiation in the stratosphere by absorbing light with a maximum wavelength of 290 nm. Absorption of a photon at 290 nm causes an O-O bond in ozone to break: O 3 O 2 + O a) What is the energy of photons with a wavelength of 290 nm, measured in kj/mol? (2) b) Draw the Lewis resonance structures for the ozone molecule, and use them to determine the O-O bond order in ozone. (3) c) Provide the molecular orbital valence electronic configuration for the O 2 molecule. (For example, the configuration for H 2 is (σ 1s 2 ). According to your configuration, what is the bond order in O 2? (3) d) Photons with a wavelength of 290 nm have enough energy to break O-O bonds in O 3, but not those in O 2, with a strength of 498 kj/mol. Are your previous answers consistent with this observation? Explain your answer, briefly. (2) Page 15 of 18

16 10 points 3.4a) Barium peroxide, (BaO 2 ), and barium carbonate, (BaCO 3 ), both decompose on heating: BaO 2 (s) BaO(s) + O 2 (g) BaCO 3 (s) BaO(s) + CO 2 (g) The reactions are not balanced. If 15.0 g of a mixture of BaO 2 and BaCO 3 are heated and after decomposition is complete, 13.0 g of BaO remains, what is the composition of the original mixture? 3.4b) If the reaction described in 3.4a is conducted in a sealed 1.50 L container that originally contains a vacuum and the 15.0 g of sample, what would the final pressure in the container be? Indicate the mole fraction of both O 2 and CO 2. (Assume the volume taken up by the solid material is both negligible and constant) Page 16 of 18

17 10 points 3.5) Draw the Lewis structure for each of the following compounds. For each compound indicate the overall shape, hybridization of the central atom, all nonzero formal charges, all bond angles, and direction of the dipole (if present). SF 3 SF 4 O 3 - IF 4 SO 4-2 Page 17 of 18

18 Data Sheet h = 6.63 x J s c = 3.00 x 10 8 m/sec m e = 9.11 x kg R H = 2.18 x J E = h ν c = λ ν 1 D = x C m R = L atm K -1 mol -1 R = J K -1 mol -1 E.N Values F(4.0), O (3.4), Cl (3.2), Br (3.0), N (3.0), S (2.6), C (2.6), H (2.2), I (2.7), K (0.8), Mg (1.2), Si (1.9) Page 18 of 18

Chemistry 121: Atomic and Molecular Chemistry Midterm 1 October 8, 2010

Chemistry 121: Atomic and Molecular Chemistry Midterm 1 October 8, 2010 /50 Total Marks Name: Student Number 1a) You are required to make a solution that has a strontium concentration of 1000 mg/l. You have strontium dichloride hexahydrate powder that you will dissolve into