Houston Community College System General Chemistry 1412 Departmental Final Exam Aspirin, C 9 H 8 O 4 - Acetylsalicylic Acid was originally derived from Salicin the active ingredient in Willow bark. drug is used today to lower fevers and reduce inflammation, especially those caused by rhumatic fever and arthritis.
PART I (2 points each) CHEM 1412 (Spring 2010) Version A-10 Multiple choice - scantron. Please DO NOT write or mark on this paper. Write your correct answer on 1. What is the molarity of a solution prepared by dissolving 25.2 g CaCO 3 in 600. ml of a water solution? A. 0.420 M B. 0.567 M C. 0.042 M D. 0.325 M 2. The Henry s law constant for CO 2 at 20ºC is k H = 3.7 X 10-2 mol/l atm. What mass of CO 2 (in grams) is present in 355 ml of a soda drink if the pressure of CO 2 in the can is 2.5 atmospheres at 20ºC? A. 4.1 g B. 1.4 g C. 0.093 g D. 0.033 g 3. Which one of the following 0.15 m aqueous solutions lowers freezing point the most? A. NaCl B. C 6 H 12 O 6 C. K 2 SO 4 D. NaNO 3 4. Which of the following molecular substances is/are soluble in CCl 4?: I 2, H 2 O, and C 8 H 18. A. only I 2 B. only H 2 O C. only C 8 H 18 D. I 2 and C 8 H 18 5. The unit for a first order rate constant is A. M s -1 B. M -1 s -1 C. s -1 D. M -2 s -1 6. For the chemical reaction A + B C, a plot of ln[a] t vs time is found to give a straight line with a negative slope. What is the order of the reaction? A. zero B. first C. second D. third 7. The rate constant for the first order decomposition of C 4 H 8 at 500 o C is 9.2x10-3 s -1. How long will it take for 10.0% of 0.100 M sample of C 4 H 8 to decompose at 500 o C? A. 12 sec B. 0.0084 sec C. 512 sec D. none 8. For the reaction CaCO 3 (s) CaO(s) + CO 2 (g), increasing the pressure on the system at equilibrium causes A.increased amount of CaCO 3 and CaO B.decreased the amount of CaO and CO 2 C.increased the amount of CO 2 and CaCO 3 D.increased the amount of CaCO 3 and CO 2
9. Phosgene, COCl 2, a poisonous gas decomposes according to the following equation; COCl 2 (g) CO(g) + Cl 2 (g) If K c = 0.083 at 900 o C, what is the value of K p? A. 0.125 B. 8.0 C. 6.1 D. 0.16 10. Consider the reaction N 2 g) + O 2 (g) 2 NO(g), K c = 0.10 at 200 o C. Starting with initial concentration of 0.04 mol/l of N 2 and 0.040 mol/l of O 2, calculate the equilibrium concentration on NO in mol/l. A. 5.4x10-3 B. 0.0096 C. 0.013 D. 1.6x10-4 11.What is the concentration of hydrogen ion in a solution with a hydroxide ion concentration of 3.81 X 10 5 M? A. 4.33 X 10 11 M B. 2.62 X 10 10 M C. 3.05 X 10 4 M D. 6.22 X 10 5 M 12. Calculate the [OH - ] in a NaOH solution with a ph of 10.33. A. 2.27 B. 4.7 X 10 11 C. 2.14 X 10 4 D. 7.3 X 10 12 13. What is the ph of a 0.035 M solution of Ca(OH) 2? A. 12.9 B. 11.8 C. 10.6 D. 13.5 14. A Bronsted-Lowry base is defined as a substance that A. acts as a proton donor B. increases [H + ] when placed in H 2 O C. decreases [OH ] when placed in H 2 O D. acts as a proton acceptor 15. What is the conjugate acid of NH 3? A. NH 3 B. NH 2 + 16. Which one of the following is the weakest acid? C. NH 3 + D. NH 4 + A. HF (K a = 6.8 X 10 4 ) B. HClO (K a = 3.0 X 10 8 ) C. HNO 2 (K a = 4.5 X 10 4 ) D. HCN (K a = 4.9 X 10 10 ) 17. Of the following four substances, which would form basic solutions? NH 4 Cl Cu(NO 3 ) 2 K 2 CO 3 NaF A. NH 4 Cl, Cu(NO 3 ) 2 B. K 2 CO 3, NH 4 Cl C. NaF only D. NaF, K 2 CO 3 18. Calculate the ph of a solution containing 0.818 M acetic acid (K a = 1.76 X 10 5 ) and 0.172 M sodium acetate. A. 4.077 B. 7.432 C. 3.568 D. 9.370
19. When a reaction is at equilibrium, its G will be A. > 0 B. = 0 C. < 0 D. none of these 20. Which one of the following pairs could be used to make a buffer solution? A. NH 3, NaC 2 H 3 O 2 B. NH 3, NH 4 Cl C. HC 2 H 3 O 2, HCl D. NaOH, NaCl 21. Which one of the following has the greatest entropy? A. HCl (l) B. HCl (g) C. HCl (s) D. all of these 22. The overall reaction 2Co 3+ (aq) + 2Cl - (aq) 2Co 2+ (aq) + Cl 2 (g) has the standard cell voltage E cell = 0.46 V. Given that Cl 2 (g) + 2e - 2Cl - (aq), E = 1.36 V, calculate the standard reduction potential for the following the half reaction at 25 C: Co 3+ + e - Co 2+ A. 1.82 V B. -0.90 V C. 0.90 V D. -1.82 V 23. According to the following cell diagram, which chemical species undergoes reduction? Sn Sn 2+ NO - 3 (acid soln), NO(g) Pt A. Sn B. Sn 2+ C. NO 3 - D. NO 24. Which statement is true for a spontaneous redox reaction carried out at standard-state conditions? A. E red is always negative B. E cell is always positive C. E ox is always positive D. E red is always positive 25. Consider the following standard reduction potentials in acid solution: The strongest oxidizing agent among those shown above is A. Fe 3+ B. Fe 2+ C. Br - D. Al 3+ 26. As a result of beta decay, the product nucleus is A. one atomic number lower than the original element B. two atomic numbers higher than the original element C. one atomic number higher than the original element D. two atomic numbers lower than the original element
27. Predict the other product of the following nuclear transformation. A. B. C. D. 28. Which is the most penetrating of the three types of nuclear radiation? A. alpha B. beta C. gamma D. two of these 29. Decay of silicon-27 by positron emission yields A. magnesium-23 B. sulfur-31 C. aluminum-27 D. silicon-26 30. The general formula for alkenes is A. C n H 2n+2 B. C 2n H 2n C. C n H n+2 D. C n H 2n 31. Which one of these hydrocarbons does not have isomers? A. C 3 H 8 B. C 6 H 14 C. C 5 H 10 D. C 4 H 8 32. The compound that has a triple bond between one pair of carbon atoms is called a/an A. alkane B. alkyl C. alkyne D. alkene 33. The alkane with six carbon atoms is called A. butane B. hexane C. heptanes D. butane 34. Which of these is the systematic name for the compound represented below? A. 1,2-dibromopropane B. 1,2-dibromopentane C. 2,3-dibromopropane D. 1,2-propane dibromide 35. Which one of these choices is the formula for a ketone? A. CH 3 CHO B. CH 3 OCH 3 C. CH 3 COCH 3 D. CH 3 COOH
Name: Part II (5 Points Each) - Please show all your work for complete credit 1. Balance the following redox reaction in basic solution and Identify the oxidizing agent and the reducing agent NO 2 (aq) + Al (s) NH 3(g) + AlO 3 (aq) 2. Consider the reaction: 2ClO 2(aq) + 2OH (aq) ClO 3 (aq) + ClO 2 (aq) + H 2 O (l) The following rate information was obtained: [ClO 2 ] [OH ] Initial Rate, - [ClO 2 ]/ t (M/s) 0.0500 0.100 0.0575 0.100 0.100 0.230 0.100 0.0500 0.115 Determine the rate law for the reaction and the rate constant for the reaction. 6
3. PCl 5 decomposes according to the equation: PCl 5(g) PCl 3(g) + Cl 2(g). At a certain temperature a 1.00 L flask initially contained 0.298 mol PCl 3(g) and 0.00870 mol PCl 5(g). After the reaction has reached equilibrium, 0.00200 mol Cl 2(g) was found in the flask. Calculate the equilibrium concentrations of PCl 5(g), PCl 3(g) and calculate the equilibrium constant K c. 4. A weak acid HA (K a = 1.0 x 10-7 ) is titrated against 0.200 M NaOH(aq). Calculate the ph after 20.0 ml of 0.200 M NaOH(aq) has been added to 50.0 ml of 0.200M HA(aq) and calculate the ph at the equivalence point. 7
5. Consider the reaction: I 2 (g) + Cl 2 (g) 2ICl(g); K p = 81.9 at 25 C. Calculate the standard free energy change. 6. Reserpine is a natural product that is used as a sedative. When 1.00 g of reserpine was dissolved in 25.0g of camphor the freezing point was lowered by 2.63 C. The freezing point depression constant, K f for camphor is 40.0 C/m. Calculate the molar mass of reserpine. 8
CHEM 1412 Final Exam Spring 2010 Version A-10 Key PART I 1. A (25.2/100) / 0.600 = 0.420 M 2.B 3. C K 2 SO 4 has three ions 2K + and SO 4 2- and lowers the freezing point more. 4. D 5. C 6. B 7. A ln(0.09) = -9.2x10-3 t + ln (0.1) solve for t = 12 sec 8. B reaction will shift to left, decreases the amounts of CO 2 and CaO 9. B n = 2-1 = 1, T = 900 + 273 = 1173 K K p = Kc (RT) n = (0.083)(0.0821x 1173) 1 = 8.0 10. C K c = [NO] 2 / [N 2 ][O 2 ] 0.1 = [NO] 2 / (0.04)(0.040) solve for [NO] = 0.013 mol/l 11. B [H + ] = 1.0x10 14 / [OH ] = (1.0x10 14 / 3.81x10 5 ) = 2.62x10 10 M 12.C ph = 10.33 poh = 14 10.33 = 3.67 [OH ] = 10 poh = 10 3.67 = 2.14x10 4 M 13.A [OH ] = n b M b = (2)(0.035) = 0.070 M poh = 1.15 ph = 12.85 = 12.9 14. D 15. D 16. D (smallest K a value) 17. D 18. A ph = pk a + Log ( M b /M a ) = 4.75 + Log (0.172/ 0.818) = 4.077 19. B 20. B 21. B 22. A 23. C 24. B 25. A 26. C 27. C 28. C 29. C 30. D 31. A 32. C 33. B 34. A 35. C PART II 5NH 3 (g) + 6AlO 3 (aq) 5NO 2 (aq) + 6Al(s) + 7H 2 O + OH (aq) Oxidizing agent = NO 2 ; Reducing agent = Al 2. Rate = k[clo 2 ] 2 [OH ] ; k= 230 M -2 s -1 3. [PCl 5 ] = 0.00670 M; [PCl 3 ] = 0.296 M; K c = 0..0884 4. ph = 6.82; ph = 10 5. G = -10.9 kj; 6. 608 g/mol 9