COLLEGE OF ENGINEERING TEST 1 TRIMESTER 2 ACADEMIC YEAR 2010/11 PROGRAM : FOUNDATION IN ENGINEERING COURSE : CHEMISTRY I COURSE CODE : CHEF 114 DATE : 10 th December 2010 DURATION : 1.5 HOUR NAME : STUDENT ID: SECTION: LECTURER : Instructions For Candidates : 1. Answer ALL the questions. 2. Please mark the answers for Section A in the answer sheet. Write the answers for Section B in the space provided. 3. All calculations in Section B must be shown clearly in order to get full marks. 4. No reference books, papers and mobile phones are allowed into the examination hall. 5. Answer Sheet for MCQ (Section A) and the Periodic Table of the elements are provided. DO NOT OPEN THIS QUESTION PAPER UNTIL YOU ARE INSTRUCTED TO DO SO This question paper has 10 pages including this page. Attendance List CHEF114 Test 1 (10 Dec 2010) Seat No: NAME : STUDENT ID: SECTION: LECTURER : SIGNATURE: 1
SECTION A Multiple Choice Questions. There is ONE best response to each question. Read all responses, choose the best one and write it on your answer booklet. Blacken the circle on the answer sheet on page 9 corresponding to this answer. Answer ALL questions. (1 mark for each question) 1. An unused flashbulb contains magnesium and oxygen. After it has been used, the contents are changed to magnesium oxide but the total mass does not change. This observation can best be explained by the A. Law of Definite Proportion. B. Law of Multiple Proportions. C. Law of Conservation of Mass. D. Avogadro s Law. E. Ideal Gas Law. 2. In Rutherford s gold foil experiment, when alpha particles are used to bombard the gold foil, most of the alpha particles pass through undeflected. This result indicates that most of the volume of a gold atom consists of A. deuterons. B. neutrons. C. protons. D. empty space. E. dense space. 3. The atomic number of an element equals to A. its atomic mass divided by two. B. the number of protons. C. the number of neutrons. D. the number of protons plus neutrons. E. the charge of the element. 2
4. Which of the following statements are true about a sample of sulfur (S) and a sample of oxygen gas (O 2 ) if the two samples are of equal mass? I. The number of electrons in the two samples is about the same. II. The number of protons in the two samples is about the same. III. The number of atoms in the two samples is about the same. IV. There are roughly twice as many sulfur atoms as oxygen atoms. V. There are roughly twice as many oxygen atoms as sulfur atoms. A. I, II, III B. I, II, and V C. II, III, IV D. III, IV, V E. II, III, V 5. Which one of the following does NOT represent 1.00 mol of the indicated substance? A. 6.02 10 23 C atoms D. 65.4 g Zn B. 26.0 g Fe E. 6.02 10 23 Fe atoms C. 12.01 g C 6. Which of the following equations does NOT represent a redox reaction? A. 2Al + 6HCl 3H 2 + 2AlCl 3 B. 2H 2 O 2H 2 + O 2 C. 2NaCl + Pb(NO 3 ) 2 PbCl 2 + 2NaNO 3 D. 2NaI + Br 2 2NaBr + I 2 E. Cu(NO 3 ) 2 + Zn Zn(NO 3 ) 2 + Cu 3
7. A 50.0 ml sample of 0.436 M ammonium nitrate (NH 4 NO 3 ) is diluted with water to a total volume of 250.0 ml. What is the ammonium nitrate concentration in the resulting solution? A. 21.8 M B. 0.459 M C. 2.18 10 2 M D. 8.72 10 2 M E. 0.109 M 8. How does the volume of 1mol of an ideal gas change if the temperature and the pressure are both decreased by a factor of four? A. decreases by four times B. decreases by sixteen times C. increases by four times D. increases by sixteen times E. remains unchanged 9. A flask contains O 2 at 25 C and 1.00 atm. Which of the statements is TRUE? A. All O 2 molecules are moving at the same speed. B. An increase in temperature will cause the average kinetic energy to increase. C. If the average speed doubles, the average kinetic energy decreases by a factor of 4. D. The average kinetic energy depends only on the pressure. E. none of the above. 10. Which of the following gases effuses at the slowest rate? A. Ar B. SF 6 C. F 2 D. Xe E. CH 4 4
SECTION B Answer ALL the questions in this section. Show your calculations clearly. All work should be done within the space provided in this question booklet. Question 1 (a) The element oxygen has three (3) naturally occurring isotopes with 8, 9 and 10 neutrons in the nucleus, respectively. (i) (ii) Write the full chemical symbols for these three isotopes. State one (1) similarity and one (1) difference between these isotopes. [3 marks] [2 marks] Answer: (i) ; ; Note to examiner: 1 point each for correct full chemical symbols, give ½ point if the element is correct but incomplete mass number or atomic number. No point given if the symbol, mass number or atomic number is wrong. (ii) Possible answers are shown in the table below. Similarities Differences All isotopes are atoms of the same elements. All isotopes have the same atomic number (or the same number of protons). All isotopes will have the same electron arrangements. Each isotope has different number of neutrons. Each isotope has different mass number. Each isotope has different atomic mass. 5
(b) Fill in the table below with the correct chemical formulas: [5 marks] Name Nitrogen trifluoride Copper(I) cyanide Chemical formula NF 3 CuCN Iodic acid HIO 3 Silver chromate Nickel(II) nitrate hexahydrate Ag 2 CrO 4 Ni(NO 3 ) 2 6H 2 O Question 2 Ethyl acetate, CH 3 CO 2 C 2 H 5, is the solvent in many fingernail polish removers. It is prepared by the reaction of ethanol, C 2 H 5 OH, with acetic acid, CH 3 CO 2 H; the other product is water. A small amount of sulfuric acid, H 2 SO 4 is used to accelerate the reaction, but the sulfuric acid is not consumed and does not appear in the balanced equation. Suppose you are given 10.0 ml each of acetic acid and ethanol: [Given: The densities of acetic acid, ethanol and ethyl acetate are 1.0492 g/ml, 0.7893 g/ml and 0.9003 g/ml, respectively. The molar masses of acetic acid, ethanol and ethyl acetate are 60.05 g/mol, 46.07g/mol, and 88.11 g/mol, respectively]. C 2 H 5 OH + CH 3 CO 2 H CH 3 CO 2 C 2 H 5 + H 2 O (a) (b) (c) Which is the limiting reactant in this reaction? [5 marks] How many ml of ethyl acetate can be prepared using this reaction? [3 marks] Which is the excess reactant in this reaction? How many moles of the excess reactant remains at the end of this reaction? [2 marks] 6
Answer: (a) Density = Mass / volume (½) Mass = density x volume 1 mol C 2 H 5 OH C 2 H 5 OH: 0.7893 g/ml x 10 ml = 7.893 g x = 0.171 mol (½) 46.07 g C 2 H 5 OH 1 mol CH 3 CO 2 H CH 3 CO 2 H: 1.0492 g/ml x 10 ml = 10.492 g x = 0.175 mol (½) 60.05 g CH 3 CO 2 H All the coefficients are 1 in the balanced equation. Mol of C 2 H 5 OH < mol of CH 3 CO 2 H, Then, (½) Ethanol (C 2 H 5 OH) is limiting reactant. (b) 0.171 mol C 2 H 5 OH x 1 mol CH 3 CO 2 C 2 H 5 x 88.11 g CH 3 CO 2 C 2 H 5 (½) 1 mol C 2 H 5 OH 1 mol CH 3 CO 2 C 2 H 5 = 15.1 g CH 3 CO 2 C 2 H 5 Volume = Mass/density = 15.1 g x (½) 1 ml CH 3 CO 2 C 2 H 5 0.9003 g CH 3 CO 2 C 2 H 5 = 16.8 ml CH 3 CO 2 C 2 H 5 (c) Excess reactant is acetic acid (CH 3 CO 2 H) 0.175 mol CH 3 CO 2 H 0.171 mol CH 3 CO 2 H = 0.004 mol CH 3 CO 2 H excess Question 3 (a) Combining Boyle s Law, Charles Law and Avogadro s Law gives the ideal gas equation. Derived the ideal gas equation using the above three laws. [5 marks] 7
(b) Acetylene, C 2 H 2, is an important fuel in welding. It is produced in the laboratory when calcium carbide, CaC 2, reacts with water: CaC 2 (s) + 2H 2 O(l) C 2 H 2 (g) + Ca(OH) 2 (s) Ans: 3 (a) A sample of acetylene, C 2 H 2 was collected over water at 23 o C. The total gas pressure was 748 mmhg and the volume was 543 ml. At 23 o C, the vapour pressure of water is 21 mmhg. What mass of acetylene in g was collected? [5 marks] Boyle s Law: PV = constant (½) Charles Law: V/T = constant (½) Avogadro s Law: n/v = constant (½) From these three equations V α 1/P ; V α T and V α n Therefore V α nt/p (½) Rearranging : PV/T α n (1) (½) Or PV/T = nr (R is the Gas constant) (½) PV = nrt (1) 3 (b) The total pressure is the sum of the partial pressures due to C2H2(g) and H2O(g): Ptotal = 748 mmhg = PH2O + PC2H2 = (21 mmhg) + PC2H2 PC2H2 = (748 21) = 727 mmhg. (½) Changing to atm unit; = 727mmHg / 760mmHg = 0.957 atm. (½) Using the ideal gas law, PV = nrt, the number of moles of C2H2 formed is: n = PV (½) RT = (0.957atm) (0.543L) (1) (0.08206Latm/K.mol) ((23 + 273)K) = 0.0214 mol (1) The molar mass of C2H2 is 26.036 g/mol. This amount therefore corresponds to a mass of, mass = number of moles molar mass = 0.0214 mol 26.036 g/mol (½) = 0.557 g (1) 8
Name : Section : Student ID : Lecturer : Answer Sheet for Multiple Choice Questions (Section A). Please use 2B pencil to fill the circle completely. Example : B D E 1. 13. 2. 14. 3. 15. 4. 16. 5. 17. 6. 18. 7. 19. 8. 20. 9. 21. 10. 22. 11. 23. 12. 24. TABLE OF CONSTANTS Avogadro's number = 6.022 x 10 23 /mol Gas constant, R = 0.0821 L.atm/ K.mol 1 atm = 760 mmhg = 760 torr = 101,325 Pa Gas constant, R = 8.314 J/ K.mol 1 J = 1 kg. m 2 / s 2 1 L.atm = 101.3 J Specific heat of water = 4.184 J/g. C 9
10 PERIODIC TABLE 1 1A 18 8A 1 H 1.008 2 2A 13 3A 14 4A 15 5A 16 6A 17 7A 2 He 4.003 3 Li 6.941 4 Be 9.012 5 B 10.81 6 C 12.01 7 N 14.01 8 O 16.00 9 F 19.00 10 Ne 20.18 11 Na 22.99 12 Mg 24.31 3 3B 4 4B 5 5B 6 6B 7 7B 8 9 10 8B 9B 10B 11 1B 12 2B 13 Al 26.98 14 Si 28.09 15 P 30.97 16 S 32.06 17 Cl 35.45 18 Ar 39.95 19 K 39.10 20 Ca 40.08 21 Sc 44.96 22 Ti 47.90 23 V 50.94 24 Cr 52.00 25 Mn 54.94 26 Fe 55.85 27 Co 58.93 28 Ni 58.70 29 Cu 63.55 30 Zn 65.39 31 Ga 69.72 32 Ge 72.61 33 As 74.92 34 Se 78.96 35 Br 79.90 36 Kr 83.80 37 Rb 85.47 38 Sr 87.62 39 Y 88.91 40 Zr 91.22 41 Nb 92.91 42 Mo 95.94 43 Tc 98 44 Ru 101.1 45 Rh 102.9 46 Pd 106.4 47 Ag 107.9 48 Cd 112.4 49 In 114.8 50 Sn 118.7 51 Sb 121.8 52 Te 127.6 53 I 126.9 54 Xe 131.3 55 Cs 132.9 56 Ba 137.3. 57 La 138.9 72. Hf 178.5 73 Ta 180.9 74 W 183.9 75 Re 186.2 76 Os 190.2 77 Ir 192.2 78 Pt 195.1 79 Au 197.0 80 Hg 200.6 81 Tl 204.4 82 Pb 207.2 83 Bi 209.0 84 Po (209) 85 At (210) 86 Rn (222) 87 Fr (223) 88 Ra (226) 89 Ac (227) 104 Rf (261) 105 Db (262) 106 Sg (266) 107 Bh (264) 108 Hs (269) 109 Mt (268) 110 Ds (269) 58 Ce 140.1 59 Pr 140.9 60 Nd 144.2 61 Pm (145) 62 Sm 150.4 63 Eu 152.0 64 Gd 157.3 65 Tb 158.9 66 Dy 162.5 67 Ho 164.9 68 Er 167.3 69 Tm 168.9 70 Yb 173.0 71 Lu 175.0 90 Th 232.0 91 Pa (231) 92 U 238.0 93 Np (237) 94 Pu (244) 95 Am (243) 96 Cm (247) 97 Bk (247) 98 Cf (251) 99 Es (252) 100 Fm (257) 101 Md (258) 102 No (259) 103 Lr (260)