2. What is the weight of 2.50 moles of ammonium sulfate, (NH 4 ) 2 SO 4?

Transcription

1 Chemistry 11 Spring 2009 Examination #2 ANSWER KEY For the first portion of this exam, select the best answer choice for the questions below and mark the answers on your scantron. Then answer the free response questions that follow (100 pts. total; multiple choice 2 pts. each). 1. The balanced equation 3H 2 (g) + N 2 (g) 2NH 3 (g) means which of the following? A. Three grams of hydrogen react with one gram of nitrogen to form two grams of ammonia. B. Three moles of hydrogen react with one mole of nitrogen to form two mole of ammonia. C. Three molecules of hydrogen react with one molecule of nitrogen to form two molecules of ammonia. D. The equation represents both (A) and (B). E. The equation represents both (B) and (C). 2. What is the weight of 2.50 moles of ammonium sulfate, (NH 4 ) 2 SO 4? A g B g C. 285 g D g E g 3. How many mg CuSO 4 are contained in x molecules CuSO 4? A x 10 6 mg CuSO 4 B x mg CuSO 4 C mg CuSO 4 D x mg CuSO 4 E mg CuSO 4 4. Which of the following is expected to be most miscible in hexane, CH 3 CH 2 CH 2 CH 2 CH 2 CH 3? A. HOCH 2 CH 2 OH B. CH 3 OH C. CH 3 CH 2 CH 2 CH 2 CH 3 D. MgCl 2 E. CH 3 COOH 1

2 5. Which of the following is a strong electrolyte? A M HCl B. 3.0 M HCl C M HF D. 3.0 M HF E. Both (A) and (B) 6. Which of the following is the weakest intermolecular interaction? A. covalent bonding B. dipole-dipole interactions C. London dispersion forces D. hydrogen bonding E. ionic bonding 7. Which gas law is most directly related to the process of inhaling and exhaling? A. Avogadro's Law B. Boyle's Law C. Charles's Law D. Dalton's Law E. Gay-Lussac s Law 8. A certain quantity of neon gas is under conditions of 798 torr at 30 ºC in a 10.0 L vessel. How many moles of neon are present? A moles B moles C moles D moles E. 321 moles 9. Which of the following constitutes a buffer solution? A. HCl and H 3 O + B. HC 2 H 3 O 2 and NaOH C. HC 2 H 3 O 2 and NaC 2 H 3 O 2 D. NaOH and H 3 O + Ε. HCl and NaOH 2

3 10. Which of the following reacts with an acid such as HCl(aq) to form a gas? A. 2 CO 3 B. OH C. 2 SO 4 D. All of the above E. None of the above 11. Consider the complete combustion of liquid octane, C 8 H 18. When the equation is balanced using smallest whole number coefficients, how many moles of oxygen gas are required? A. 8 B. 16 C. 18 D. 24 E Water is likely to be a poor solvent for which type(s) of molecules? A. molecules which can form dipole-dipole interactions B. molecules which can form hydrogen bonds C. nonpolar molecules D. polar molecules E. None; water is considered a universal solvent 13. Saline solutions (NaCl in water) used to deliver intravenous drugs are 0.89% (w/v). What weight of NaCl is found in 500. ml of such a solution? A g B g C g D. 4.5 g E. 8.9 g 14. Which of the following is TRUE of the vapor pressure of a liquid? A. The vapor pressures of all liquids are the same. B. The vapor pressure of a liquid is an equilibrium pressure. C. The vapor pressure of a liquid can be measured in an open container. D. The vapor pressure of a liquid is independent of temperature. E. The vapor pressure of a liquid in dynamic equilibrium cannot be determined. 3

4 15. Which of the following conditions characterizes STP? A. 0 C and 1 atm B. 0 F and 1 atm C. 0 K and 1 atm D. 1 C and 0 atm E. 1 K and 0 atm 16. Which of the following is NOT a strong base? A. Ba(OH) 2 B. KOH C. Na 2 O D. MgO E. NH 4 OH 17. A gas is expanded from an initial volume of 20.5 L at mm Hg and 23.0 C to a final volume of 34.6 L. During the expansion, the gas cools to 12.0 C. What is the final pressure (in atm)? A atm B atm C atm D atm E. 1.9 atm 18. When comparing two separate closed containers containing C 2 H 5 OH(l) and (CH 3 ) 2 O(l), respectively, which of the following is/are TRUE? I. C 2 H 5 OH(l) has a higher expected boiling point than (CH 3 ) 2 O(l). II. C 2 H 5 OH(l) has a lower vapor pressure than (CH 3 ) 2 O(l). III. C 2 H 5 OH(l) exhibits hydrogen bonding with itself. IV. (CH 3 ) 2 O(l) exhibits hydrogen bonding with itself. V. (CH 3 ) 2 O(l) exhibits an expected greater surface tension than C 2 H 5 OH(l). A. I only B. II and III C. IV only D. IV and V E. I, II, and III 4

5 19. Given the following boiling points: acetic acid (117.9 C), chloroform (61.7 C), ethanol (78.5 C) and water (100.0 C), which of these liquids is MOST volatile? A. acetic acid B. chloroform C. ethanol D. water E. All are equally volatile. 20. When solutions of silver nitrate and sodium hydroxide are mixed together, sodium nitrate (which is soluble) and a black precipitate are formed. Although it might be thought that the precipitate is silver hydroxide, analysis shows that it is actually Ag 2 O. Which of the following is the correct balanced net-ionic equation for the formation of Ag 2 O from AgNO 3 (aq) and NaOH(aq)? A. 2AgNO 3 (aq) + 2NaOH(aq) 2NaNO 3 (s) + Ag 2 O(s) + H 2 O(l) B. 2Ag + (aq) + 2OH (aq) Ag 2 O(s) + H 2 O(l) C. 2Ag + (aq) + 2NO 3 (aq) + 2Na + (aq) + 2OH (aq) 2Na + (aq) + 2NO 3 (aq) + 2Ag + (aq) + O 2 (aq) + H 2 O(l) D. 2Ag + (aq) + 2NO 3 (aq) + 2Na + (aq) + 2OH (aq) 2Na + (aq) + 2NO 3 (aq) + Ag 2 O(s) + H 2 O(l) E. 2Ag + (aq) + NO 3 (aq) + 2OH (aq) Ag 2 O(s) + H 2 O(l) + NO 2 (g) 21. Which of the following correctly describes the condition of acidosis? A. The blood ph lies between 7.0 and 7.3. B. A patient may feel tired, disoriented, and have difficulty breathing. C. This condition may be caused by fever and rapid breathing (hyperventilation). D. Both (A) and (B) E. All of the above describe acidosis mole of hydrogen peroxide, H 2 O 2, contains how many moles of hydrogen atoms? A B C D E

6 23. A gas occupies 3.8 L at 0.70 atm pressure. If we expand the volume at constant temperature to 6.5 L, what is the final pressure (in atm)? A atm B atm C. 1.2 atm D. 2.4 atm E. 35 atm 24. Two ions comprising a buffer system that play an important role in biochemistry are produced from which of the following acids? A. acetic B. boric C. nitric D. carbonic E. phosphoric 25. Which of the following does NOT correctly characterize ideal gases? A. Gases are compressible. B. Gases assume the shape/volume of their container. C. Gases are in continuous, random motion. D. The average kinetic energy of gas molecules does not change with time as long as temperature remains constant. E. Gases exist ideally under conditions of low temperature and high pressure. 26. (10 pts. total) When solutions of AgNO 3 and NaCl react, the balanced molecular equation is AgNO 3 (aq) + NaCl(aq) AgCl(s) + NaNO 3 (aq). A. (8 pts.) How much AgCl is produced when 3.10 g of AgNO 3 and 3.10 g of NaCl react? g AgCl = 3.10 g AgNO 3 x 1 mol AgNO 3 x 1 mol AgCl x g AgCl g AgNO 3 1 mol AgNO 3 1 mol AgCl = 2.62 g AgCl g AgCl = 3.10 g NaCl x 1 mol NaCl x 1 mol AgCl x g AgCl g NaCl 1 mol NaCl 1 mol AgCl = 7.60 g AgCl 6

7 B. (2 pts.) If a student obtains 1.93 g of AgCl in the laboratory, what is the percentage yield in the experiment? Percent Yield = 100 (Actual Yield/Theoretical Yield) = 100 (1.93 g/2.62 g) = 73.7% 27. (12 pts. total; 4 pts. each) Write BALANCED equations (net ionic where appropriate) for each laboratory situation. Assume that solutions are aqueous unless otherwise indicated. Write NR if no reaction occurs. A. Solid zinc is mixed with chromium(iii) nitrate. 3Zn(s) + 2Cr +3 (aq) 3Zn +2 (aq) + 2Cr(s) B. Barium chloride is reacted with sodium sulfate. Ba +2 (aq) + SO 4-2 (aq) BaSO 4 (s) C. Lead pellets are combined with hydrochloric acid (HCl). Pb(s) + 2H + (aq) + 2Cl - (aq) PbCl 2 (s) + H 2 (g) 28. (18 pts. total) Pretend you are a lab technician doing a titration experiment in the laboratory. You want to standardize an aqueous solution of sulfuric acid using sodium hydroxide base. Answering the questions that follow will help you standardize the acid. A. (5 pts.) What mass (in g) of solid sodium hydroxide is required to prepare 400 ml of 0.75 M NaOH(aq)? 400 ml x 0.75 moles/1000 ml = 0.3 moles of NaOH 0.3 moles NaOH x g/1 mole NaOH= or 12 g NaOH Dissolve 12 g NaOH in 400 ml of D.I water to make 0.75 M NaOH B. (10 pts.) If 25.0 ml of an aqueous solution of H 2 SO 4 requires 19.7 ml of 0.75 M NaOH to reach the end point, what is the molarity of the H 2 SO 4 solution? H 2 SO 4 (aq) + 2NaOH(aq) Na 2 SO 4 (aq) + 2H 2 O(l) 7

8 M sulfuric acid = 0.75 mol NaOH x L x 1 mol H 2 SO 4 4 x (0.025 L) -1 L 2 mol NaOH = 0.30 M H 2 SO 4 (aq) C. (3 pts.) What is the equivalence point of a titration? The point in the titration at which enough titrant has been added to react exactly with the substance being determined (i.e. mol H + = mol OH - ). 29. (10 pts. total; 5 pts. each) The following are concentrations for a couple of human biological materials, namely milk and urine. A. From the [H + ] of milk, calculate the corresponding ph. Classify milk as acidic, basic, or neutral. Milk, [H + ] = 7.94 x 10-8 M ph = -log[h + ] = 7.10 A. From the [OH - ] of urine, calculate the ph of urine and classify urine as acidic, basic, or neutral. Urine, [OH - ] = 3.98 x 10-8 M poh = -log[oh - ] = 7.40 ph = 14 poh =