NAME Student ID No. Section (circle one): A01 (Dr. Lipson) A02 (Dr. Briggs) A03 (Dr. Brolo) UNIVERSITY OF VICTORIA Version A CHEMISTRY 102 Term Test I February 4, 2011 Version A This test has two parts: (A Data Sheet is provided with the exam.) PART I is a multiple choice examination and is worth 26 marks. The answers for the 14 questions in this part must be coded on the optical sense form using a soft-leaded pencil. PART II has written answer questions and is on the last 3 pages and is worth 24 marks. Answer these questions on this examination paper. Part II Score Exam results Score 1 [3 marks] 6. [4 marks] 2 [4 marks] Part I multiple choice [26 marks] 3 [4 marks] Part II written [24 marks] 4 [3 marks] Total score [50 marks] 5. [6 marks] Percent score Hand in this entire test paper as well as your optical sense form (bubble sheet) at the end of the examination period (60 minutes) PART I Multiple Choice. Select the best response from the choice provided. Mark only one response for each question. 1. This is exam version A. Mark "A" as the answer to question 1 2. A sample of O 2 gas with a volume of 0.357 L was collected at 21 o C. Calculate the volume in liters of the gas when it is cooled to 10 o C if the gas is ideal and the pressure remains constant. A. 0.171 B. 0.290 C. 0.344 D. 0.357 E. 0.371
Chem 102, Midterm 1 Version A page 2 of 7 3. Vessel A contains CO(g) at 0 C and 1 atm. Vessel B contains SO 2 (g) at 0 C and 1 atm. The two vessels have the same volume. Which of the following statement(s) are TRUE (i) Vessel A contains more molecules. (ii) Vessel B contains more mass of gas. (iii) The average kinetic energy of molecules in Vessel B is higher. (iv) The root mean square (rms) speed of molecules in Vessel A is higher. A. (i) & (ii) B. (i) & (iii) C. (iii) & (iv) D. (ii) & (iv) E. (i) & (iv) 4. A container holds a mixture of oxygen, neon and helium gases. The partial pressures are 150 torr for oxygen, 300 torr for neon and 450 torr for helium. What is the mole fraction for neon? A. 0.17 B. 0.33 C. 0.50 D. 0.67 E. 2.0 5. Consider the following 5 gases. If an equal mass of each gas is placed into a separate balloon, which gas sample will have the greatest volume? Assume that the balloons are all at the same temperature and pressure. A. He B. H 2 C. N 2 D. Ne E. O 2 6. Consider three samples of gas: N 2 at 273 K, H 2 at 350 K and O 2 at 350 K. Compare the average kinetic energies of the molecules in these three samples. A. Additional pressure information is needed to compare average kinetic energies. B. The heaviest gas (O 2 ) has the highest average kinetic energy and the other average kinetic energies decrease with molar mass. C. O 2 (350 K) and H 2 (350 K) have the same average kinetic energy while N 2 (273 K) has a lower average kinetic energy D. O 2 (350 K) and H 2 (350 K) have the same average kinetic energy while N 2 (273 K) has a higher average kinetic energy E. The lightest gas (H 2 ) has the highest average kinetic energy and the other average kinetic energies decrease as molar mass increases.
Chem 102, Midterm 1 Version A page 3 of 7 7. Which one of the following statements about the earth s atmosphere is CORRECT? A. The mechanism for restoring the ozone layer over Antarctica involves the formation of polar stratospheric clouds B. The first step in the formation of ozone in the stratosphere is a photodissociation reaction. C. All wavelengths of solar radiation can initiate photoionization reactions. D. The temperature of the atmosphere steadily decreases with increasing altitude. E. The hole in the ozone layer over Antarctica is of constant depth and size throughout the year. 8. Suppose that the mid-day concentration of NO 2 in the ground-level air in a city is 0.020 ppm by volume. Calculate the number of moles of NO 2 in 1.0 L of this air at STP (i.e. at 0 C and 1 atm). A. 2.0 x 10-8 B. 8.9 x 10-10 C. 0.45 D. 4.5 x 10-7 E. 0.02 9. It has been suggested that one way to repair the problem of stratospheric ozone depletion would be to manufacture ozone, carry it to the stratosphere, and release it. It has been estimated that it would take about 17 million airplane-loads of ozone to replenish even 10% of the stratospheric ozone. The best reason(s) that such as solution is impractical is/are: (i) Even if we could temporarily replace the lost ozone, the natural steady-state ozone cycle would quickly be re-established at the pre-existing lower ozone concentrations. (ii) Ozone is too heavy to transport. (iii) The sudden burst of ozone would cause a climate warming problem. (iv) Ozone is too reactive to be stored in tanks for transport. (v) Ozone, being denser than oxygen, would sink to the earth s surface and cause damage. A. i B. iii and iv C. ii and v D. i and iv E. i, ii, iii, iv, and v 10. Which of the following gases are greenhouse gases? A. O 2, H 2 O B. CO 2, N 2 C. N 2, H 2 O D. CO 2, O 2, H 2 O E. CO 2, H 2 O, CH 4
Chem 102, Midterm 1 Version A page 4 of 7 11. In North America, what is the main human-caused source of the sulfur dioxide (SO 2 ) that contributes to such pollution problems as acid rain? A. Burning gasoline in cars and trucks. B. Burning coal and heavy oil for electricity, heating, and industry. C. Volcanic gases and forest fires. D. Mining of sulfur. E. Decomposition of atmospheric sulfur trioxide (SO 3 ). 12. Which of the following statements is NOT CORRECT? A. Visible and ultraviolet radiation wavelengths reach the earth s surface and this energy is re-emitted by the earth as infra-red radiation (heat). B. Absorption of infra-red radiation increases vibrational energy in a molecule. C. NO 2 in the atmosphere is a significant contributor to the problem of acid rain. D. CO 2, CH 4, and water vapour are all greenhouse gases. E. Unburned hydrocarbons in the stratosphere are a significant contributor to the problem of photochemical smog. 13. Which of the following reactions is/are NOT a significant process in the usual set of reactions that maintain the protective stratospheric ozone layer? (i) O(g) + O 2 (g) > O 3 * (g) (ii) O 2 (g) + 2NO(g) > 2NO 2 (g) (iii) O 3 (g) + hv > O 2 (g) + O(g) A. (i) B. (ii) C. (iii) D. (i) and (ii) E. (ii) and (iii) 14. A system that does not do work but absorbs heat from the surroundings has A. q > 0 and ΔE < 0 B. q > 0 and ΔE > 0 C. q < 0 and ΔE > 0 D. q < 0 and ΔE < 0 E. q > 0 and ΔE = 0
Chem 102, Midterm 1 Version A page 5 of 7 Part II Written Answer (3 marks) 1. Consider the following data about three identical flasks, numbered 1, 2, and 3. Each flask contains a sample of one gas; one flask contains hydrogen gas (H 2 ), another nitrogen (N 2 ), and a third argon gas (Ar). o Each flask contains 4.00 grams of the gas. o At the same temperature, the pressure in Flask #1 is lower than the pressure in Flask #2. o In order for the pressure in Flask #3 to be equal to the pressure in Flask #2, Flask #3 must be cooled to a lower temperature. Identify which gas is in which flask. Show your reasoning. Point 1 tells us that the flasks contain different numbers of moles of gases. Point 2 tells us that there are more moles of gas in flask #2 than in flask #1. Point 3 tells us that there are more moles of gas in flask #3 than in flask #2. Therefore, moles gas in flask #3 > moles gas in flask #2 > moles gas in flask #1 Therefore, flask #3 must contain the lightest gas and flask #1 the heaviest. So, flask #1 is Ar, flask #2 is N 2, and flask #3 is H 2. (4 marks) 2. A piece of sodium metal reacts completely with water as follows: 2 Na (s) + 2 H 2 O (l) 2 NaOH (aq) + H 2 (g) The hydrogen gas generated is collected over water at 23.0 C. The volume of the gas collected is 323 ml measured at 1.010 atm pressure. Calculate the number of grams of sodium metal consumed in the reaction. (The vapour pressure of water at 23.0 C is 0.0277 atm.) (There s extra space on next page.) P(hydrogen) = 1.010 atm 0.0277 atm = 0.9823 atm chemical amount H 2 = PV/RT = 0.9823 atm 323 ml 101325 N m -2 atm -1 10-6 m 3 ml -1 8.314 J mol -1 K -1 (273.15 + 23.0) K 1 N m J -1 chemical amount H 2 = 0.01306 mol chemical amount Na used = 2 0.01306 mol = 0.02612 mol mass of Na consumed = 0.02612 mol 22.99 g mol -1 = 0.600 g (three sig fig)
Chem 102, Midterm 1 Version A page 6 of 7 (4 marks) 3. Suppose 1000 moles of oxygen gas (O 2 ) is compressed into a steel tank that has a volume of 45.0 L. (a) Assuming that oxygen behaves as an ideal gas, and that the temperature of the gas and tank is 0 C, calculate the pressure inside the tank in atmospheres. P = nrt/v = (1000 mol 8.314 J mol -1 K -1 273.15 K)/ 0.045 m 3 = 5.047 10 7 N m -2 (=5.047 10 7 Pa) converting to atmosphere units P = 5.047 10 7 N m -2 atm = 498 atm 101325 N m -2 (b) The actual pressure for the real gas in the tank described above is 1026 atm. Explain briefly the reason for any difference between this value and the result of your calculation in part (a) above. The real value is higher because molecules take up space, and at high pressures this becomes important. (3 marks) 4. Assume that the kinetic energy of a 1400 kg car moving at 115 km h -1 can be converted entirely into heat by putting on the brakes and bringing the car to a stop. (a) How much heat (in kilojoules) is that? E k = (1/2)mv 2 = (1/2) 1400 kg ((115 10 3 m h -1 )/ 3600 s h -1 ) 2 = 700 kg 1020.4 m 2 s -2 E k (all converted to heat in bringing the car to v=0) = 714313 J = 714 kj (b) Suppose that this car is brought to a stop by using its brakes. If we define the system to be the car, is the internal energy change (ΔE) positive, negative, or zero when the car is brought to a stop using its brakes? (Hint: The brakes get hot.) Circle the correct answer. positive negative zero
Chem 102, Midterm 1 Version A page 7 of 7 6 marks 5. [4] a) Write two chemical equations to show the main mechanism of formation of ozone in the stratospheric ozone layer. O 2 (g) + hv 2 O (g) O (g) + O 2 (g) O 3 * [2] b) Write a chemical equation to show the main method of natural destruction of ozone in the stratosphere. O 3 (g) + hv O 2 (g) + O(g) 4 marks 6. Hemoglobin is the protein that transports O 2 through the blood from the lungs to the rest of the body. In doing so each molecule of hemoglobin combines with four molecules of oxygen (O 2 ). The toxicity of the pollutant gas carbon monoxide (CO) arises because it binds more tightly to hemoglobin than does oxygen. If 1.00 g of hemoglobin combines with 1.53 10-6 m 3 of CO at 37 o C and 99.0 kpa, what is the molar mass of hemoglobin? 1 hemoglobin + 4CO products for CO, n = PV/RT = 99.0 10 3 Pa 1.53 10-6 m 3 8.314 J mol -1 K -1 (273.15 + 37) K = 5.874 10-5 mol CO moles hemoglobin combined = (1/4) 5.874 10-5 mol = 1.469 10-5 mol molar mass hemoglobin = (mass)/(moles) = 1.00g/1.469 10-5 mol = 68096 g/mol = 6.81 10 4 g/mol ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~END~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~