Chem 105 Final Exam. Here is the summary of the total 225 points plus 10 bonus points. Carefully read the questions. Good luck!

Transcription

1 May 3 rd, 2012 Name: CLID: Score: Chem 105 Final Exam There are 50 multiple choices that are worth 3 points each. There are 4 problems and 1 bonus problem. Try to answer the questions, which you know first, and then solve the problems, which you are not sure about. Here is the summary of the total 225 points plus 10 bonus points. Carefully read the questions. Good luck! Multiple choices (50 total) 3 points each, the total is 150 points Problems #1 15 points #2 20 points #3 15 points #4 25 points #5 (Bonus) 10 points Total 235 points You could use your calculator. No notes or books of any sort may be used during the exam. I have neither given nor received aid on the exam. Signature and date 1

2 I. Multiple Choices: (3 points each, 150 total points; Choose the best answer for each question) 1. Two natures of light are wave and particle. Wave nature means to have and particle nature of light is a) an electric field component and a magnetic field component; quantum b) an electric field component and a magnetic field component; photon c) emission and absorption; quantum d) emission and absorption; photon 2. Which of the four quantum numbers (n, l, m l, m s ) determines the orientation of an orbital and which of the four quantum numbers (n, l, m l, m s ) determines the shape of an orbital respectively? a) l; m l b) m l ; n c) m l ; l d) n; m l 3. What is the correct order of the electromagnetic spectrum from shortest wavelength to longest wavelength? a) Gamma Rays X-rays Ultraviolet Radiation Visible Light Infrared Radiation Microwaves Radio Waves d) Gamma Rays X-rays Visible Light Ultraviolet Radiation Infrared Radiation Microwaves Radio Waves c) Radio Waves X-rays Ultraviolet Radiation Visible Light Infrared Radiation Microwaves Gamma Rays b) Visible Light Infrared Radiation Microwaves Radio Waves Gamma Rays X-rays Ultraviolet Radiation 4. The maximum number of electrons that can occupy an energy level described by the principal quantum number, n, is. a) n b) n + 1 c) 2n d) 2n 2 5. The first ionization energy is the minimum energy required to remove the first electron from the atom in its ground state. Which of the following atoms most likely has the highest first ionic energy? a) 9 F b) 12 Mg c) 15 P d) 56 Ba 2

3 6. The hybridization of N in the NH 3 molecule is in which new type of orbitals are generated. a) sp 2 ; 2 b) sp 2 ; 3 c) sp 3 ; 3 d) sp 3 ; 4 7. Determine Hº rxn for the reaction 2Al 2 O 3 (s) 4Al(s) + 3O 2 (g). You are given: 2Al(s) + (3/2)O 2 (g) Al 2 O 3 (s), and Hº rxn = 1,670 kj/mol a) 835 kj/mol b) 1,670 kj/mol c) 2,357 kj/mol d) 3,340 kj/mol L of gas A at 1.00 atm and 1.00 L of gas B at 1.00 atm are combined in a 3.00 L flask. The flask is sealed and over time they react to completely to give gas C according to the following chemical equation: 2A(g) + B(g) C(g). Assume constant temperature condition. a) 0.33 atm b) 0.50 atm c) 0.67 atm d) 1.0 atm 9. A ground-state atom of manganese has unpaired electrons and is. a) 0, diamagnetic b) 2, diamagnetic c) 0, paramagnetic d) 2, paramagnetic 10. Which of the following bonds has the longest bond length and which of the following bonds has the highest bond energy respectively? a) C N; C N b) C N; C N c) C N; C N d) C N; C N 11. Which one of the following pairs are isoelectronic? a) Cl - and S b) K + and Cl c) Na + and K + d) Zn 2+ and Cu + 3

4 12. Which of the following substance is/are trigonal pyrimidal? 2 (i) SO 3 (ii) SO 3 (iii) NO 3 (iv) PF 3 (v) BF 3 a) only (i) and (ii) b) only (i), (iii), and (v) c) only (ii), and (iv) d) all are trigonal pyrimidal except (v) 13. Arrange the following ions in order of increasing ionic radius: Na +, N 3, O 2, F. a) F < O 2 < N 3 < Na + b) F < O 2 < Na + < P 3 c) N 3 < O 2 < F < Na + d) Na + < F < O 2 < N Give the number of lone pairs around the central atom and the molecular geometry of AsCl 3. a) 0 lone pair; trigonal planar b) 1 lone pair; trigonal pyrimidal c) 2 lone pairs; T shape d) 3 lone pairs; linear 15. The correct order of increasing polarity is. a) C-N < C-O < C-F < F-F b) C-O < C-F < F-F < C-N c) F-F < C-F < C-O < C-N d) F-F < C-N < C-O < C-F 16. According to the valence shell electron pair repulsion (VSEPR) theory, the geometry of the SO 2 molecule is and the geometry of the SO 3 molecule is a) linear; trigonal planar b) linear; trigonal pyrimidal c) bent; trigonal planar d) bent; trigonal pyrimidal 17. A single pulse of a laser yields an average of photons with λ = 633 nm. If melting ice to water at 0 C requires 6.01 kj/mol, what is the fewest number of laser pulses need to melt 10.0 g of ice? h = 6.63 x J s a) 2,127 b) 3,343 c) 3,833 d) 38,330 4

5 18. What is the maximum number of electrons in an atom that can have the following set of quantum numbers? n = 4; l = 3; m l = 2; m s = +1/2 a) 1 b) 2 c) 6 d) The standard enthalpy change for the following reaction is. 2C 8 H 18 (l) + 17O 2 (g) 16CO(g) + 18H 2 O(l) given two following reactions: 2C 8 H 18 (l) + 25O 2 (g) 16CO 2 (g) + 18H 2 O(l) H = 11,020 kj/mol 2CO(g) + O 2 (g) 2CO 2 (g) a) -4,326 kj/mol b) -6,492 kj/mol c) -10,454 kj/mol d) -11,586 kj/mol H = kj/mol 20. The enthalpy change for the combustion of one mole of acetylene, C 2 H 2, to form carbon dioxide and water vapor is -1,010.5 kj. The reaction is under constant pressure and volume condition. What is the bond energy of C C (BE C C ) in kj/mol? Type of Bonds Bond Energy (kj/mol) C H 456 C C 347 C=C 620 C=O 802 O=O 499 O H 462 a) 799 kj/mol b) 962 kj/mol c) 1,035 kj/mol d) 1,277 kj/mol 21. How many liters of chlorine Cl 2 gas at 2.50 x 10 C and atm can be produced by the reaction of 12.0 g of MnO 2 with excess HCl according to the following chemical equation? The molar mass of MnO 2 : g/mol and the molar mass of Cl 2 : 70.9 g/mol, R = L atm/(mol K). (K = C + 273) MnO 2 (s) + 4HCl(aq) MnCl 2 (aq) + 2H 2 O(l) + Cl 2 (g) a) L b) L c) 1.09 L d) 3.55 L 5

6 22. What are the correct numbers of dots surrounding the 33 As symbol in the Lewis dot structure of 33 As and surrounding the 33 As 3- symbol in the Lewis dot structure of 33 As 3- respectively? a) 3; 0 b) 3; 6 c) 5; 0 d) 5; A ml sample of M HNO 3 is completely neutralized by 352 ml Al(OH) 3. What is the concentration in molarity of Al(OH) 3? 3HNO 3 + Al(OH) 3 Al(NO 3 ) 3 + 3H 2 O a) M b) M c) M d) M 24. An aluminum (Al) metal reacts with hydrochloric acid (HCl) to form hydrogen gas (H 2 ) and aluminum chloride. If the volume of H 2 gas is L and the pressure of H 2 gas is 1.05 atm after the end of the reaction. Temperature of H 2 gas is 22ºC. Calculate how many gram of Al was used in the reaction. Assuming the percent yield is 100%. R = atm L/(K mol) a) g b) g c) g d) g 25. Three students (X, Y, Z) are assigned the task of determining the mass of a sample of iron. Each student makes three determinations with a balance. The results in grams are X (61.5, 61.6, 61.4); Y (62.8, 62.2, 62.7); Z (61.9, 62.2, 62.1). The actual mass of the iron is 62.0 g. Student is the least precise and student is the most accurate. a) X; Y b) X; Z c) Y; X d) Y; Z 26. Ethylene (C 2 H 4 ) burns in oxygen to form carbon dioxide (CO 2 ) and water vapor. How many liter(s) of CO 2 are obtained from 1.00 liter (L) of O 2 at the constant temperature and pressure? C 2 H 4 + 3O 2 2CO 2 + 2H 2 O a) L b) 1.00 L c) 1.50 L d) 2.00 L 6

7 27. Predict the geometry and polarity of the CS 2 molecule. a) Bent; Nonpolar b) Bent; Polar c) Linear; Nonpolar d) Linear; Polar 28. Indicate the type of hybrid orbitals used by the central atom in PF 3. a) sp b) sp 2 c) sp 3 d) sp 3 d 29. Use the bond enthalpy data given to estimate the heat released when 50.0 g of propane gas, C 3 H 8, burns in excess oxygen to yield carbon dioxide and water vapor at 25 C. Type of Bonds Bond Energy (or Enthalpy) (kj/mol) C C 347 C C 962 O=O 498 C=O 799 O H 460 C H 414 a) 1362 kj/mol b) 1544 kj/mol c) 2248 kj/mol d) 2378 kj/mol 30. The Lewis structure for a carbonic ion, CO 3 2-, should show single bond(s), double bond(s), and lone pair(s). a) 2, 1, 7 b) 2, 1, 8 c) 3, 0, 7 d) 3, 0, A chemist wishes to perform the following reaction: N 2 + 3H 2 2NH 3 If only 28.2 g of N 2 is available, what is the minimum amount, in grams, of H 2 needed to completely react with this quantity of N 2? a) 1.01 g b) 1.51 g c) 3.03 g d) 6.06 g 7

8 32. Which of the following ionic solids would have the smallest lattice energy? a) KF b) KI c) LiF d) NaF g of glucose (C 6 H 12 O 6 ) is dissolved in L of water. The molarity (M) of the glucose solution is. Assume that the final volume of the glucose solution is L. a) M b) M c) 1.00 M d) 10.0 M 34. Calculate the density in g/l, of CO 2 gas at 2.70 x 10 C and atm pressure. R = L atm/(mol K). The molar mass of CO 2 : 44.0 g/mol. (K = C + 273) a) g/l b) 1.12 g/l c) 2.93 g/l d) 4.02 g/l 35. You are given a balanced reaction: 2H 2 + O 2 2H 2 O. How many moles of water could be made from 5.0 mol H 2 and 3.0 mol O 2 at the end of the reaction? a) 1.5 mol b) 3.0 mol c) 5.0 mol d) 8.0 mol 36. What is the oxidation number of S in H 2 SO 4? a) -2 b) +2 c) +4 d) What mass of Li 3 PO 4 is needed to prepare 5.00 x 10 2 ml of a solution having a lithium ion concentration of M? a) 3.38 g b) 6.75 g c) 10.1 g d) 19.3 g 8

9 38. Give the values of all the quantum numbers associated with the electron in 3d shown in the following diagram. 1s 2s 2p 3s 3p 4s 3d a) ψ = fn(3, 1, -1, -1/2) b) ψ = fn(4, 1, -1, -1/2) c) ψ = fn(3, 2, -2, -1/2) d) ψ = fn(4, 2, -2, -1/2) 39. The correct order of increasing electronegativity is. a) As < Ga < K < Cs b) Cs < K < Ga < As c) Ga < As < K < Cs d) K < Ga < As < Cs 40. List the following atoms and ions in an order of increasing atomic size: K +, Cl -, Ar, Ca 2+, Cl a) Ar < K + < Ca 2+ < Cl < Cl - b) Ca 2+ < K + < Ar < Cl < Cl - c) Cl < Cl - < Ar < K + < Ca 2+ d) K + < Ca 2+ < Ar < Cl < Cl According to Bohr s theory, an electron originally in a higher-energy orbital falls back to a lower-energy orbital. As a result, a photon is given off. Calculate the wavelength, in nanometers, of the light emitted by a hydrogen atom when its electron falls from the n = 7 to the n = 4 principal energy level. R H = 2.18 x J and h = 6.63 x J s. a) nm b) nm c) nm d) nm 42. According to Bohr s theory, an electron originally in a higher-energy orbital falls back to a lower-energy orbital. As a result, a photon is given off. Calculate the frequency in s -1 (Hz) of the light emitted by a hydrogen atom during a transition of its electron from the n = 6 to the n = 3 principal energy level. R H = 2.18 x J and h = 6.63 x J s. a) s -1 b) s -1 c) s -1 d) s -1 9

10 43. Valence shell and valence electrons of an atom of tellurium ( 52 Te) are respectively? a) 5; 4 b) 5; 6 c) 6; 4 d) 6; Electrons in an atom have the quantum numbers n = 3, l = 1, m l = 0. Name the orbital in which these electrons would be found. a) 3d yz b) 3p y c) 3d xz d) 3p x 45. Give the values of the four quantum numbers of an electron in the orbital of 3d. a) n: 3; l: -2; m l : -2; m s : +1/2, -1/2 b) n: 3; l: -2; m l : -2, -1, 0, +1, +2; m s : +1/2, -1/2 c) n: 3; l: +2; m l : -2; m s : +1/2, -1/2 d) n: 3; l: +2; m l : -2, -1, 0, +1, +2; m s : +1/2, -1/2 46. Which of the following atom and/or ions has/have this electron configuration? 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 5 a) Fe 2+ and Co 2+ b) Fe 2+ and Cu 2+ c) Mn d) Mn and Co The electron configurations of Zn 2+ and Ge are respectively. a) 1S 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 8 ; 1S 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 2 b) 1S 2 2s 2 2p 6 3s 2 3p 6 4s 0 3d 10 ; 1S 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 2 c) 1S 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 8 ; 1S 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 6 4p 6 d) 1S 2 2s 2 2p 6 3s 2 3p 6 4s 0 3d 10 ; 1S 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 6 4p The formal charge of C in HCN is. a) -2 b) -1 c) 0 d) +1 10

11 49. The total number of lone pair in the NO 2 ion is and the formal charge of N in the NO 2 ion is. a) 4; -1 b) 4; 0 c) 6; -1 d) 6; A 2.50-L flask contains a mixture of methane (CH 4 ) and propane (C 3 H 8 ) at a pressure of 1.45 atm and 20.0 C. When this gas mixture is then burned in excess oxygen, 8.60 g of carbon dioxide is formed. The other product is water. What is the mole fraction of propane in the original gas mixture? R = L atm/(mol K) a) b) c) d) II. Problem Solving 1. Show all the resonance forms of HNO 3. Calculate the formal charges for N atom and three O atoms in all the resonance forms of HNO 3. Show your calculations for the formal charges of any one of the resonance forms of HNO 3. (Total 15 points and showing the calculation is 4 points) 11

12 2. Write Lewis structures for the following molecules. (20 points, 4 points each) (a) CH 4 O 2 (b) H 3 PO 4 (c) CO (d) C 2 H 5 Cl (e) CH 4 N 2 O 12

13 3. Draw the dipole moment for each bond and the resultant dipole moment if not zero, for the following molecules. Specify whether each molecule is nonpolar or polar. Justify your answers. (15 points, 5 points each) (i) CH 4 (ii) SO 2 (iii)h 2 O 4. When a g sample of an organic compound C x H y O z containing C, H and O is burned in completely in oxygen, 1.35 g of CO 2 and g of H 2 O are produced. What is the empirical formula of the compound? Show your calculations. (25 points) 13

14 5. Bonus question (total 10 points). IT IS GREAT TO KNOW YOU! I BELIEVE YOU HAVE TRIED YOUR BEST IN THIS COURSE! HAVE A GOOD WINTER BREAK! BEST WISHES! (a) What is the molar concentration of chloride ions in a solution prepared by mixing 50.0 ml of 2.00 M KCl with ml of a 1.50 M CaCl 2 solution? Assume the final volume is additive. Show your calculations or justify your answer. (5 points) (b) Show the Lewis structure of N 2 O and calculate the formal charges on the two nitrogen atoms and one oxygen atom in N 2 O? Show your calculations. (5 points) 14

15 15