BCIT Fall Chem Exam #1

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Agnes Cameron
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1 BCIT Fall 2012 Chem 3615 Exam #1 Name: Attempt all questions in this exam. Read each question carefully and give a complete answer in the space provided. Part marks given for wrong answers with partially correct reasoning/calculations. A Periodic Table and formula sheet are attached at the back. Total points = 50 Good Luck. 1

2 Section I: (20 points total, 1 point each) Choose the BEST answer to the following questions. 1. Which of the following is not a property of a gas?. a) expands to fill the volume f any container b) much lower densities than solids and liquids c) highly variable densities, depending on conditions d) characteristics odors detected by the human olfactory e) changes volume dramatically with changing temperature 2. All of the following factors influence the height of a column of a liquid that will be supported by atmospheric pressure except a) the diameter of the liquid column b) the value of the atmospheric pressure c) the density of the liquid d) the value of the acceleration due to gravity e) all of the above will affect the height of the liquid column 3 5. Four identical 1.0 L flasks contain the gases He, Cl 2, CH 4, and NH 3, each at 0C and 1 atm pressure. Assume ideal gas conditions. 3. Which gas sample has the greatest density? a) He b) Cl 2 c) CH 4 d) NH 3 e) all gases are the same 4. For which gas sample do the molecules have the highest average kinetic energy? a) He b) Cl 2 c) CH 4 d) NH 3 e) all gases are the same 5. For which gas sample has the greatest number of molecules? a) He b) Cl 2 c) CH 4 d) NH 3 e) all gases are the same 2

3 6. If a deep sea diver ascends to the surface (1 atm) from a pressure of 5 atm, the volume of the dissolved gas bubbles in the diver's blood will increase by a factor of during the ascent. a) 0.1 b) 0.2 c) 1 d) 5 e) Two gaseous elements, A and B, react to form only gaseous product, X, as follows: 1 L of A(g) + 2 L of B(g) 1 L of X(g) Which of the following is a formula for the product that is consistent with the data? a) AB b) A 2 B c) AB 2 d) All of the above are consistent e) None of the above are consistent 8. Consider the commercial production of SO 3 via the unbalanced reaction below: SO 2 (g) + O 2 (g) SO 3 (g) If 5.3 L of SO 2 and 4.7 L of O 2 are mixed how much SO 3 may be produced, all gases are at STP? a) 4.7 L b) 5.3 L c) 9.4 L d) 10.0 L e) 10.6 L 9. As the temperature of a gas increases, the area under the Maxwell Boltzmann distribution of molecular speeds curve: a) increases b) remains the same c) decreases d) multiplies by a constant e) more information is needed 10. All of the following are true about the speed of a gas according to the kinetic theory except a) The root mean square speed of a gas depends on the pressure. b) The particles move at different speeds. c) The root mean square speed of a gas is proportional to the square root of the temperature in K. d) Particles with high molar masses in a gas mixture move more slowly than those with low molecular masses. e) When a particle collides with a wall its speed before and after the collision are the same. 3

4 11. When does the ideal gas law begin to break down? a) as the attractive forces between molecules becomes significant b) as the volume of the molecules becomes significant compare to the volume of the container c) at low temperatures d) at high pressures e) all of the above 12. Which of the following is true about a real gas? a) Its pressure is always less than that calculated for an ideal gas b) Its pressure is always greater than that calculated for an ideal gas c) Its pressure is always different than that calculated for an ideal gas d) Its particles have volume and have forces of attraction or repulsion for other particles e) More than one of the above is true. 13. What will be the likely value of the compressibility factor, Z, of a real gas if attraction between particles is the predominant factor causing non ideal behavior? a) Z will be less than 1 b) Z will be equal to 1 c) Z will be greater than 1 d) Z will be equal to 0 e) Unable to predict 14. A beam of light with a wavelength of 450 nm is expelling electrons from a lithium surface. What will be the effect of changing to 400 nm at the same intensity? a) No effect b) Increase only in the kinetic energy of expelled electrons c) Increase only in rate electrons are of expelled from the surface d) Increase both in the kinetic energy and rate of electrons are expelled from the surface e) Unable to predict 15. All of the following are assumptions made in the Bohr model of the atom except a) The forces of circular motion and coulombic attraction exactly balance. b) The electron can occupy only certain orbits c) If an electron stays in a fixed orbit it neither absorbs or emits energy d) The nucleus contains protons and neutrons e) All the above assumptions are made 4

5 16. Which of the following is not true of the Bohr model of the atom a) The Bohr model accurately reproduces the spectrum of hydrogen atoms. b) The Bohr model involves quantum numbers c) The Bohr model predicts the emission spectrum of small atoms such as He and Li d) The orbiting electron in the ground state maintains a constant distance from the nucleus e) All the above are true 17. Which of the following statements is (are) true? I. An excited atom can return to its ground state by absorbing electromagnetic radiation. II. The energy of an atom is increased when electromagnetic radiation is emitted from it. III. The energy of electromagnetic radiation increases as its frequency increases. IV. An electron in the n = 4 state in the hydrogen atom can go to the n = 2 state by emitting electromagnetic radiation at the appropriate frequency. V. The frequency and wavelength of electromagnetic radiation are inversely proportional to each other. a) II, III, IV b) III, V c) I, II, III d) III, IV, V e) I, II, IV 18. As an electron moves closer to the nucleus, energy is a) absorbed b) released c) remains unchanged d) transformed into a proton 19. What is the energy necessary to remove one electron from the Be 3+ ion? a) 1.36x10 19 J b) 5.45x10 19 J c) 2.18x10 18 J d) 8.71x10 18 J e) 3.48x10 17 J 20. Why is wavelike behavior not observed for a moving car? a) It has no charge b) Its speed is too slow. c) Its mass is too great. d) It is not a pure substance. 5

6 Section II: Calculations and reasoning must be shown (30 points total) 21. An angioplasty balloon has a volume of 1.0 cm 3 and contains an inert gas mixture at 0.95 atm at room temperature, 20 C. What is the resulting pressure of the balloon if the temperature is increased to 37 C (body temperature) and the volume reduced to 0.85 cm 3? (2 points) Note that the number of moles is constant.. ³. ³ What is the molar mass of an ideal gas which has a density of 13.5 g/l at a pressure of 1.50 atm and a temperature of 27 C? (3 points) / 23. A gas mixture of N 2 (g) and CO 2 (g) is in a 10.0 L container. At a temperature of 273 K, the total pressure is atm. The mixture is known to contain 3.00 g of N 2 (g). What is the partial pressure of CO 2 (g) in the mixture (4 points) or

7 24. A L flask at 25 C contains mol of N 2 gas at 25 C. a) Calculate the pressure using the ideal gas law (2 points) b) Calculate the pressure using the van der Waals equation. The a and b values for N 2 are a = atm L 2 mol 2 and b = L/mol (3 points) / c) Comment on if N 2 behaves as an ideal gas under these conditions. (1 point) The ~ 1.5% difference in pressure shows that the N 2 behaves pretty much as an ideal gas under these conditions. Since Z = 0.99 < 1 the dominant deviation is that there is a slight attraction between the molecules under these conditions. 7

8 25. Is it likely that there is a hydrogen atom with an electron of energy 1.00x10 19 J? Explain your answer. (3 points) For hydrogen atom Z = 1, use equation for hydrogen atom energies and solve for n ² ² ² Since n is not an integer, there will not be any hydrogen atoms with an electron of energy 1.00x10 19 J. 26. What is the longest wavelength of light that can be absorbed by a hydrogen atom in its lowest energy state? (3 points) Longest wavelength corresponds to the lowest energy, hence it will be when the electron goes from the n = 1 n=2 orbit. For hydrogen Z = ,678 ² ,678 1² 1 1² 1 2² 1 82,259, Consider an electron confined to the width of a nucleus, 1x10 15 m. What would be the minimum uncertainty in its velocity? (2 points) Δ Δ Δ Δ 4 For the minimum value Δ 4Δ 4Δ Δ 4Δ / 8

9 28. Using the root mean square speed calculate the gas temperature of Xe for which = 0.35 nm nm is a typical wavelength needed to resolve diffraction from the surface of a metal crystal. On the basis of your results do you think Xe would be a good choice to use for diffraction from a metal surface? (4 points) , putting into the first equation ² ² This is so cold that Xe is unlikely to be useful 29. Photogray lenses incorporate small amounts of silver chloride in the glass of the lens. The following reaction occurs in the light, causing the lenses to darken: AgCl x10 2 kj/mol Ag + Cl 3.10x10 2 kj/mol is required to make this reaction occur. Assuming all this energy is supplied by light, what is the maximum wavelength of light that can cause this reaction to occur? (3 points)

10 Equations and Formulas PV = nrt ² ² ² T(K) = T( C) R = L atm mol 1 K 1 = J mol 1 K 1 = Pa m³ mol 1 K 1 k = 1.38x10 23 J/K c = 3.00x10 8 m/s m e = 9.11x10 31 kg h = 6.63x10 34 J s N A = 6.02x10 23 g = 9.81 m s 2 P = hgd ² ² Δ ² ,678 ² 1 1 ² a 0 = 52.9 pm p = mv E = hf c = f E photon = E Binding + E electron h mv h x p 4 10

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Gas Laws. Gas Properties. Gas Properties. Gas Properties Gases and the Kinetic Molecular Theory Pressure Gas Laws

Gas Laws. Gas Properties. Gas Properties. Gas Properties Gases and the Kinetic Molecular Theory Pressure Gas Laws Gas Laws Gas Properties Gases and the Kinetic Molecular Theory Pressure Gas Laws Gas Properties 1) Gases have mass - the density of the gas is very low in comparison to solids and liquids, which make it