e - S18 Chem111 Exam 3 5,7,8 Sect 1,2

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Dec 6, 2023

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0 Name:_________________________________________________________________ Packet 1 of 2 Spring 2018 Exam 3 Written Section 1, 2 Lab Instructor: Malette Lab Instructor: Entus ab Instructor: Farnum Instructions: Be sure to read each question completely before you begin the answer it. For questions that require calculations, you are expected to show all relevant work, clearly indicating formulas used, and appropriate units. Unless a question is specifically requesting appropriate sig figs, you are expected to give at least 3 or 4 sig figs in the answer (with the appropriate units). If your work is not clear or inappropriate you may lose up to all credit for question, regardless of the correctness of the final answer. No additional paper will be accepted with the exam, if you need addition space to show work, use the back side of one of the pages and clearly indicate the location of the work in the problem. You may choose one question that may be in either section 1 or 2, place a large X through the question to clearly indicate the choice, and receive full credit for the question regardless of the work shown. If more than one question is selected, only the first will receive credit. This selection is not obligatory and you may answer all questions; failure to clearly indicate a skipped question, a small x through the number is not acceptable, will result in all questions getting graded. NOTE: The multiple-choice answers must be on the answer sheet provided on your cheat sheet and work shown for credit. Constants: Avagadro’s number = 6.022 x 10 23 Plank’s constant= 6.626 x 10 -34 Js Speed of light = 3.00 x 10 8 m/s Rydberg constant = 2.18 x 10 -18 J electron mass = 9.109 x 10 -28 g Gas Constant = 0.0821 L atm/mol K Gas Constant = 8.314 J/mol K Neutron mass= 1.675 x 10 –24 g; eut Equations for volume: Sphere = 4/3πr 3 Cylinder = πr 2 h Cube = lhw

1 Section I. (50pts total / 5pts per question) All questions must show appropriate work to get credit for a correct answer. Incorrectly answered questions will receive partial credit based on work. Be sure to read all questions completely. 1.1 (5pts). Calculate the energy of the light emitted by a hydrogen atom during a transition of its electron from the n = 7 to the n = 2 principal energy level Answer:_________________________ 1.2 (5pts). An instrument, maintained at 100 ° C, has two separate flasks that contain different gases. If the flasks are opened so that the gases are able to mix, what is the final pressure in flask 2 Flask Gas Pressure (atm) Volume (Liters) 1 fluorine 5.00 1.50 2 Iodine 3.75 3.50 Answer:_________________________ 1.3 (5pts). If 255 mL of hydrogen gas is collected over water at an atmospheric pressure of 730 mmHg and 55 ○ C, how many moles of hydrogen are present? Answer:_________________________ 1.4 (6pts). What is the maximum number of electrons in a atom that can have the following set of quantum numbers? Note: if the space contains (---) no quantum number is assigned. n l m l m s # electrons 3 --- --- --- 28 4 --- 0 --- 8 1 1 --- +1/2 0 2 0 --- --- 2 5 3 1 --- 4 1.5 (5pts). Arrange the listed elemental gasses, using their chemical symbols, in increasing order for the following: density, kinetic energy, radius (of a single atom), and velocity at 125 ○ C and 310 ○ C. If the values are equal, place an X through the <. Iodine, Fluorine, Xenon, Neon 25 ○ C 210 ○ C density: ________ < ________ < ________ < ________ density: ________ < ________ < ________ < ________ KE: ________ < ________ < ________ < ________ KE: ________ < ________ < ________ < ________ radius: ________ < ________ < ________ < ________ radius: ________ < ________ < ________ < ________ Vel: ________ < ________ < ________ < ________ Vel: ________ < ________ < ________ < ________

2 Section II (48pts total / 8pts per question) partial credit given for work shown, AND work is required for credit, even if correct answer is given. 2.1 (8pts). Calculate the heat of reaction for the following equation. Be sure to show all equations for full credit, not just numbers. Al 3+ (g) + 2 Br - (g) → Al + (g) + 2 Br (g) 0.35 mol ch4 -->492.6 nm Answer:_________________________ 2.2 (8pts). The longest wavelength of light that causes electrons to be ejected from the surface of a copper plate is 355 nm. What is the maximum velocity of the electrons ejected when light of wavelength 300. nm shines on a copper plate >7,500 L Answer:_________________________ 2.3 (8pts). Electrons can be used to probe the arrangement of atoms on a solid surface if the wavelength of the electrons is comparable with the spacing between the atoms. What electron velocity would be appropriate for use in this application if the atoms are separated by 0.220 nm? Answer:_________________________

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3 2.4 (8pts). Air contains 78% nitrogen, 21% oxygen, and 1% argon, by volume. What is the density of air at 760.0 mmHg and –10°C? ch Answer:_________________________ 2.5 (8pts). A 0.271 g sample of an unknown vapor occupies 294 mL at 140.°C and 847 mmHg. The empirical formula of the compound is CH 2 . What is the molecular formula of the compound? Answer:_________________________ 2.6 (8pts). The following took place in a 55.0 L vessel. If 11.75 g of FeS 2 and 8.45 atm of O 2 (at 398 K) are allowed to react completely, determine the pressure of SO 2 (g) in the vessel at standard temperature. The molar mass of FeS 2 is 119.99 g/mol. 4 FeS 2 (s) + 11 O 2 (g) → 2 Fe 2 O 3 (s) + 8 SO 2 (g) -->9560 Answer:_________________________