CHEM Lab Section Number: Name (printed): Signature:...(d) The gas behaves according to the ideal gas...

CHEM 200/202 Spring 2019 Exam 3-A April 27, 2019

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CHEM _______ Lab Section Number: _____ Name (printed):_____________________________________________

Signature:______________________________________

This exam consists of 36 questions all of equal value for a total of 225 points. Make sure that your test has all of the pages. Please read each problem carefully. There are no intentionally misleading questions; each problem should be taken at its face value. Please mark your answers on the Scantron sheet provided to you and on the actual exam.

You will be given a periodic table and an exam information sheet to use during the exam. You may remove it from the exam make it more accessible. You may also use the designated Casio fx-300ms-plus calculator or equivalent non-programmable non-graphing scientific calculator during the exam. Use the back pages of the test as scratch paper. You are not allowed to use any devices capable of accessing the internet, textbooks, notes, or homemade reference sheets during the exam.

You may leave if you finish the exam early. Give the exam and the information sheet to your TA and leave quietly without disturbing other students. Before leaving, check that all your answers have been properly entered on the Scantron sheet and the exam and that your name is written on every page of the exam and on the Scantron sheet.

All cell phones and electronic devices must be turned off and put away. Please remove all hats and caps. Place your books and all papers out of sight under your seat. If the TA believes that you might be looking at your neighbor’s paper, you will be asked to move to a new location.

Exam scores will be posted on Blackboard as soon as the grading is complete. Your test will be returned to you in the first lab meeting of next week. If you have any questions regarding the grading of your exam, please notify your TA.

The time available for the exam is 120 minutes. Good luck!


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Name: ___________________________________________ Lab Section #: _______ Please mark your answers on the scantron sheet using a #2 pencil and also mark your answers on the exam itself. Mark Test From “A” on your scantron. 1. Hydrogen gas exerts a pressure of 466 torr in a container. What is this pressure in

atmospheres?

(a) 0.613 atm (b) 0.466 atm (c) 0.217 atm (d) 1.63 atm (e) 4.60 atm

2. A sample of an ideal gas has its volume doubled while its temperature remains constant. If

the original pressure was 100 torr, what is the new pressure?

(a) 50 torr (b) 10 torr (c) 100 torr (d) 200 torr (e) 1000 torr

3. A weather balloon was initially at a pressure of 0.950 atm, and its volume was 35.0 L. The pressure decreased to 0.750 atm, without loss of gas or change in temperature. What was the change in the volume?

(a) Increased by 9.3 L (b) Decreased by 27.6 L (c) Increased by 7.4 L (d) Decreased by 7.4 L (e) Increased by 44.3 L

4. A balloon filled with 3.72 moles of nitrogen gas has a pressure of 1.42 atm at 23.5°C. The

balloon expands as the temperature of the gas inside the balloon increases to 47.0°C. If the final pressure of the gas inside the balloon is 1.52 atm, what is the volume of the balloon?

(a) 63.8 L (b) 0.500 L (c) 128 L (d) 64.3L (e) 87.3 L


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5. A 3.50 gram mass of a pure solid is placed into an, empty, sealed, 675 mL container, and it is heated until it becomes a gas. Once it has become a gas, at 249°C, the pressure inside the container is 8.23 atm. What is the molar mass of the solid?

(a) 27.0 g/mol (b) 14.2 g/mol (c) 0.0370 g/mol (d) 32.4 g/mol (e) 19.3 g/mol

6. What is the density (in g/L) of nitrogen gas (N2) when the gas has been pumped into a 50.0

L balloon, at 23.8°C, and it has a pressure of 1.71 atm?

(a) 2.50 g/L (b) 1.33 g/L (c) 7.02 g/L (d) 1.97 g/L (e) 1.03 g/L

7. A gas 4.91 L cylinder has been filled with 25.0 grams of argon gas, 1.97 moles of neon gas,

and 0.723 moles of xenon gas. What is the pressure inside the cylinder when it is at 32.1°C?

(a) 13.7 atm (b) 21.9 atm (c) 85.7 atm (d) 18.3 atm (e) 16.9 atm

8. When considering a container which holds a gas, and the ideal gas law, which of these

statements is incorrect?

(a) When all other factors are held constant, the pressure is directly proportional to the temperature of the gas.

(b) When all other factors are held constant, the volume is inversely proportional to the number of moles of gas.

(c) When all other factors are held constant, the temperature is directly proportional to the volume of the gas.

(d) When all other factors are held constant, pressure is inversely proportional to the volume of the gas.

(e) When all other factors are held constant, the temperature is inversely proportional to the number of moles of gas.


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9. An ideal gas is heated from 298 K to 354 K in a steel container. Which quantity will remain unchanged?

(a) The pressure of the gas. (b) The density. (c) The collision frequency of the gas molecules. (d) The kinetic energy of the gas molecules. (e) All of these will change.

10. A sample of ammonia gas at 65.5°C and 524 torr has a volume of 15.31 L. What is its

volume when the temperature is –15.8°C and its pressure is 524 torr?

(a) 3.69 L (b) 20.2 L (c) 11.6 L (d) 63.5 L (e) 0.01 L

11. A 750-mL sample of hydrogen exerts a pressure of 822 torr at 325 K. What pressure does it

exert if the temperature is raised to 475 K at constant volume?

(a) 188 torr (b) 562 torr (c) 1.11 x 103 torr (d) 1.20 x 103 torr (e) 1.90 x 103 torr

12. Calculate the temperature of an argon sample at 55.4 kPa and 18.6 L if it occupies 25.8 L

at 75.0°C and 41.1 kPa.

(a) 65.2°C (b) 95.0 °C (c) 72.9°C (d) 77.2°C (e) 85.1°C

13. A gas mixture consists of equal masses of methane (molecular weight 16.0) and argon

(atomic weight 40.0). If the partial pressure of argon is 200. torr, what is the pressure of methane, in torr?

(a) 80.0 torr (b) 200. torr (c) 256 torr (d) 500. torr (e) 556 torr


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14. Which of the following gases will be the slowest to diffuse through a room?

(a) Hydrogen sulfide (b) methane (c) water (d) carbon dioxide (e) neon

15. Select the statement which does NOT apply to an ideal gas.

(a) There are no attractive forces between the gas molecules. (b) There are strong repulsive forces between the gas molecules. (c) The volume occupied by the molecules is negligible compared to the container

volume. (d) The gas behaves according to the ideal gas equation. (e) The average kinetic energy of the molecules is proportional to the absolute

temperature.

Consider this structure for the following four questions. The four carbon atoms are numbered for reference in the questions.

16. Based on formal charge calculations, on which atom of the structure given above is the positive charge primarily located?

(a) C1 (b) C2 (c) C3 (d) O (e) N

17. What is the hybridization of C1?

(a) unhybridized (b) sp (c) sp2 (d) sp3 (e) sp3d


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18. What is the hybridization of O?


19. What is the hybridization of N?


20. What are the formal charges of each non-hydrogen atom of these two isomers and which

one is more stable?

(a) 0, 0, 0 (left to right for A); −1, +1, 0 (left to right for B); A is more stable (b) 0, 0, 0 (left to right for A); −1, +1, 0 (left to right for B); B is more stable (c) −1, +1, 0 (left to right for A); 0, 0, 0 (left to right for B); A is more stable (d) −1, +1, 0 (left to right for A); 0, 0, 0 (left to right for B); B is more stable (e) 0, 0, 0 (left to right for A); 0, 0, 0 (left to right for B); same stability

21. What is the difference between isomers and resonance structures?

(a) Resonance structures are different molecules that rapidly interconvert, whereas

isomers are different molecules that slowly interconvert. (b) Resonance structures are different representations of the same molecule,

whereas isomers are distinct molecules that do not have the same properties. (c) Resonance structures are molecules whose electrons oscillate in response to an

electric field, while isomers have a symmetrical distribution of electrons that makes then unresponsive to electric fields.

(d) Resonance structures are different shapes of the same molecule due to bond vibrations, whereas isomers are symmetrical molecules whose shape is not affected by bond vibrations.

(e) They’re the same: resonance structures and isomers are synonymous.


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22. Using the provided bond dissociate energies, calculate ΔH° for the given reaction.

Bond Bond Dissociation Energy / kJ·mol−1

C–H 415 C–C 345 C=C 611 C–Br 275 H–H 436 H–Br 370 Br–Br 190

(a) −320 kJ·mol−1 (b) 95 kJ·mol−1 (c) −95 kJ·mol−1 (d) 54 kJ·mol−1 (e) −54 kJ·mol−1

23. Considering the following energy diagram, what should be in the place of the question

marks?

(a) ΔHf° = -306.3 kJ/mol (b) ΔHf° = -350.1 kJ/mol (c) ΔHf° = -756.9 kJ/mol (d) ΔHlattice° = -350.1 kJ/mol (e) ΔHlattice° = -756.9 kJ/mol


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24. What is the molecular shape of BrF3 as predicted by VSEPR theory?

(a) trigonal pyramidal (b) linear (c) T-shaped (d) see-saw (e) tetrahedral

25. What is the hybridization of Br in BrF3?

(a) sp (b) sp2 (c) sp3 (d) sp3d (e) sp3d2

26. Considering the following Lewis structure of formaldehyde, which two types of orbital

overlap accurately describe the C=O bond?

(a) σ (overlap of 𝐂𝒔𝒑𝟐 and 𝐎𝒔𝒑𝟐) and π (overlap of 𝐂𝟐𝒑 and 𝐎𝟐𝒑) (b) π (overlap of C'() and O'()) and σ (overlap of C+( and O+() (c) σ (overlap of C'() and O'()) and π (overlap of C'() and O'()) (d) σ (overlap of C'(, and O'(,) and π (overlap of C+( and O+() (e) σ (overlap of C'() and O'()) and σ* (overlap of C+( and O+()

27. In which type of orbital is each of the unshared pairs on oxygen of formaldehyde (figure in

problem 26)?

(a) 2s (b) 2p (c) sp (d) sp2 (e) sp3

28. By applying VSEPR and bond polarity, which of these molecules is nonpolar?

(a) PCl5 (b) CHCl3 (c) NH3 (d) H2O (e) BrF4−

Either A or E.


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29. What are the H-B-H bond angles in BH3?

(a) slightly greater than 109.5° (b) slightly less than 109.5° (c) slightly greater than 120° (d) exactly 120° (e) slightly less than 90°

30. What are the F-S-F bond angles in SF4?

(a) 90° (b) 109.5° (c) 120° (d) slightly less than 90° and slightly less than 120° (e) slightly less than 90°

Use the molecular orbital diagrams below to answer the following two questions.

31. For the molecule O2−, the bond order is

(a) 0 (b) 0.5 (c) 1 (d) 1.5 (e) 2

32. For the molecule F2, how many valence electrons are in antibonding orbitals?

(a) 2 (b) 3 (c) 4 (d) 5 (e) 6


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33. Which of these two structures represents the true geometry of I3− and why?

(a) Bent I3− is accurate because the closely spaced unshared pairs provide a lot of room

for the negative charge.. (b) Linear I3− is accurate because, in VSEPR theory, atoms take up more space than

unshared pairs. (c) Bent I3− is accurate because, in VSEPR theory, atoms take up more space than

unshared pairs. (d) Linear I3− is accurate because, in VSEPR theory, unshared pairs take up more

space than atoms. (e) Bent I3− is accurate because, in VSEPR theory, unshared pairs take up more space

than atoms.

34. How are antibonding orbitals produced in orbital mixing?

(a) Destructive interaction (phase mismatch) between atomic orbitals. (b) Constructive interaction (phase match) between atomic orbitals. (c) When the nuclei of two atoms approach one another too closely, the repulsion

between their positive charges overwhelms the benefits of electron sharing, resulting in an antibonding state.

(d) When the shapes of the orbitals are not matched by symmetry and cannot overlap, antibonding results.

(e) Mixing hybridized with unhybridized orbitals always produces antibonding orbitals. 35. What is the fundamental difference between σ and π bonds?

(a) σ bonds represent efficient orbital overlap between atoms of similar electronegativity

and π bonds describe weak orbital overlap between atoms of different electronegativity.

(b) σ bonds are always lower in energy than π bonds. (c) σ bonds represent electron density within one standard deviation of the position of

the nucleus and π bonds exist within the volume (4/3)πr3, where r is the distance between the nuclei.

(d) σ bonds have a continuous lobe of electron density between the nuclei and π bonds have a node of zero electron density centered between the nuclei.

(e) σ bonds are fully symmetrical about the bond axis and π bonds have electron density on opposite sides of the bond axis (e.g. above and below).


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36. The molecule formate is described by two resonance structures, shown below. Given your understanding of the meaning of resonance, what can you say about the hybridization of the two O atoms?

(a) One is sp3 and the other is sp2. (b) Both are sp3. (c) Because of the definition of resonance, they have to have the same

hybridization. (d) They undergo rapid rehybridization. (e) None of these are correct.


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CHEM Lab Section Number: Name (printed): Signature:...(d) The gas behaves according to the ideal gas...

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