Final Exam F22 Key

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Chem 103-4 Final Exam Date last revised 12/19/2022 Page 1 of 8 CHEMISTRY 103-4 Name __ Key _ ______________________________ FINAL EXAM December 19, 2022 Sec _________ TA ___________________________ INSTRUCTIONS: 1. Do not separate the pages of the exam. 2. PRINT your name, discussion section number, and TA’s name at the top of this page NOW. 3. The scantron form is machine-scored and must be filled out using a #2 pencil. PRINT your last name and the first 5 letters of your first name on the scantron form as it appears in Canvas, then fill in the circles corresponding to the letters in your name. Write your student ID number under “Identification Number”, and fill in the circles. Write your lecture number ( 4 ) under “Special Codes”. 4. Write your answers to the multiple-choice questions in this test booklet, then transfer your answers to the scantron form. Only the scantron form will be graded. 5. Answer the remaining short answer questions directly in the space provided in this exam. Report all numerical answers with the correct number of significant figures and units. Show all relevant work to receive full credit. 6. Complete the following exam by yourself. You will be given 120 minutes. 7. When you are finished, turn in your scantron form and exam. 8. Read and sign the Honor Code statement. Honor Code: I affirm that I will not give or receive any unauthorized help on this exam, and that all work will be my own. Signature question 26 _________/26 question 27 _________/21 question 28 _________/12 question 29 _________/8 question 30 _________/8 _________/75 Short Answer Total Thanks for a great semester and HAPPY HOLIDAYS!!!

Chem 103-4 Final Exam Date last revised 12/19/2022 Page 2 of 8 Enter your answers to the following questions on the scantron form. Each question is worth 3 points . There is ONE best response to each question. 1. Sodium azide, NaN 3 , is an ionic compound that contains the azide polyatomic ion. What is the chemical formula of the azide ion? A. N 3– B. N – C. N 3 3– D. N 3 – E. N 2 2. Which of the following reaction types does not necessarily give a visible indication of reaction? A. Precipitation reaction B. Gas forming reaction C. Neutralization reaction D. All of the above always give visible indication of reaction 3. Which of the following 1.0-gram samples has the lowest percentage of metal? A. MgO B. LiF C. ZnI 2 D. PH 3 E. KBr 4. Which of the following salts is expected to have the highest melting point? A. LiF B. BeO C. NaCl D. KBr E. CsI 5. Which atom contains the smallest number of protons? A. 51 V B. 50 Cr C. 54 Cr D. 55 Mn E. 57 Fe 6. Which of the following aqueous solutions is the weakest conductor of electric current? A. 0.1 M HClO 4 B. 0.1 M HNO 3 C. 0.1 M H 3 PO 4 D. 0.1 M H 2 SO 4 E. All solutions will have the same conductivity 7. Choose the reducing agent in the reaction below. H + (aq) + NO 3 – (aq) + 2NO(g) + H 2 O(l)  3HNO 2 (aq) A. H + B. N C. O D. NO 3 – E. NO

Chem 103-4 Final Exam Date last revised 12/19/2022 Page 3 of 8 8. Element X is triatomic, existing as X 3 molecules. It also consists of two naturally occurring isotopes, 29 X (60% natural abundance) and 31 X (40% natural abundance). How many peaks would be expected in the soft mass spectrum of X 3 ? A. 2 B. 3 C. 4 D. 5 E. 8 9. When 25 mL of 0.10 M HCl(aq) and 25 mL of 0.10 M NaOH(aq) are mixed, an exothermic reaction occurs releasing thermal energy into the surroundings, and the resulting 50 mL solution increases in temperature. Which combination of reactants would result in a solution with the same magnitude of temperature change after their mixing? A. 10 mL of 0.10 M HCl(aq) and 10 mL of 0.10 M NaOH(aq) B. 50 mL of 0.20 M HCl(aq) and 50 mL of 0.20 M NaOH(aq) C. 100 mL of 0.20 M HCl(aq) and 100 mL of 0.20 M NaOH(aq) D. 25 mL of 0.20 M HCl(aq) and 75 mL of 0.20 M NaOH(aq) E. None of the above 10. For the following combustion reaction, where there are more gaseous products compared to reactants, what are the correct signs for Δ H and w? C 2 H 5 OH(l) + 3O 2 (g)  2CO 2 (g) + 3H 2 O(g) A. Δ H > 0 w > 0 B. Δ H > 0 w < 0 C. Δ H < 0 w > 0 D. Δ H < 0 w < 0 11. Which of the following has the largest second ionization energy? A. Li B. Na C. K D. Ca E. Mg 12. Copper has 2 stable isotopes, 63 Cu and 65 Cu. Knowing that the atomic weight of copper is 63.55, estimate the approximate percentage of 63 Cu. A. 10% B. 45% C. 55% D. 70% E. 95% 13. An aqueous solution contains either CaCl 2 or Ca(OH) 2 . Which of the following reagents can be added to distinguish between the two compounds? A. ZnCl 2 B. KOH C. AgNO 3 D. NH 4 Cl E. BaSO 4

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Chem 103-4 Final Exam Date last revised 12/19/2022 Page 4 of 8 14. What form of electromagnetic radiation is used to obtain 3D structural information? A. Blue light B. X-rays C. Microwaves D. Radio waves E.  -rays 15. Which of the following transitions in the H atom emits radiation with the lowest energy? A. n=2  n=1 B. n=3  n=2 C. n=4  n=3 D. n=4  n=1 E. n=5  n=4 16. What is the maximum number of electrons that can reside in the n = 3 electron shell? A. 2 B. 4 C. 9 D. 18 E. 32 17. For which of the following elements do the two 1s electrons experience the largest effective nuclear charge Z eff ? A. He B. Ne C. Ar D. Kr E. all the same 18. Which of the following ions has the largest ionic radius? A. Ca 2+ B. K + C. Cl - D. S 2- E. Se 2- 19. The enthalpy change for which of the following reactions corresponds to  H f °[MgCl 2 (s)]? A. Mg 2+ (aq) + 2 Cl – (aq)  MgCl 2 (s) B. Mg 2+ (g) + 2 Cl – (g)  MgCl 2 (s) C. Mg(s) + 2 Cl(g)  MgCl 2 (s) D. Mg(s) + Cl 2 (g)  MgCl 2 (s) E. None of the above 20. In which of the following species is the C–O bond order 1.5? A. CO 2 B. CO 3 2– C. CH 3 OH D. CO E. none 21. Which of the following species does not obey the octet rule? A. O 3 B. CO 2 C. NO 2 D. CS 2 E. none

Chem 103-4 Final Exam Date last revised 12/19/2022 Page 5 of 8 22. Which gas has the highest density at standard temperature and pressure (STP)? A. O 3 B. CO 2 C. NO 2 D. He E. all the same 23. Which gas particles have the highest root-mean-square (rms) speed, v rms , at 300 K? A. O 3 B. CO 2 C. NO 2 D. He E. all the same 24. A flask contains 2.5 g of each O 3 , CO 2 , NO 2 , and He. Which gas exerts the greatest partial pressure? A. O 3 B. CO 2 C. NO 2 D. He E. all the same 25. What is the correct electron domain structure of the molecule BrF 3 ? A. B. C. D. E. Br F F F Br F F F Make sure to enter your multiple-choice answers on the scantron form!

Chem 103-4 Final Exam Date last revised 12/19/2022 Page 6 of 8 PART 2 – Short Answer (26 total pts on this page) 26. (26 pts total) The following data can be found in the literature for benzene , (78.11 g/mol): Normal melting point (m.p.): 278.7 K Normal boiling point (b.p.): 353.3 K Critical point (c.p.): 562 K, 46.78 atm Triple point (t.p.): 278.5 K, 0.0477 atm a) (8 pts) Use these data to sketch a phase diagram in the space provided below. Label the normal m.p., normal b.p., c.p., t.p., and the gas, liquid and solid regions. Temperature (K) 200 250 0.1 1.0 10 100 300 350 400 450 500 550 600 650 700 Gas b.p. m.p. c.p. t.p. Liquid b) (2 pts) What is the highest pressure at which solid benzene sublimes? _ 0.0477 _ atm c) (2 pts) What is the lowest pressure at which liquid benzene exists? _ 0.0477 _ atm d) (2 pts) What is the vapor pressure of liquid benzene at 353.3 K? _ 1.00 _ atm e) (4 pts) Solid benzene is more / less [circle one] dense than liquid benzene because… [finish sentence] the slope of the line representing the solid/liquid interface is positive. +2 pts: correct answer circled +2 pts: answer mentions positive slope of line representing solid/liquid interface or that the temperature of the triple point is lower than the normal melting point f) (4 pts) Use the P and T values for the t.p. and b.p. provided above to calculate the enthalpy of vaporization,  H vap . 𝛥𝐻 vap ൌ 𝑅 ൈ 𝑙𝑛 ቀ 𝑃 ଶ 𝑃 ଵ ቁ ቀ 1 𝑇 ଵ െ 1 𝑇 ଶ ቁ ൌ 8.314 ൈ 𝑙𝑛 ቀ 1.00 0.0477 ቁ ቀ 1 278.5 െ 1 353.3 ቁ J/mol ൌ 33.3 kJ/mol +2 pts: correct equation/setup; +2 pts: correct value. (-1 pt: sig. figs <2 or >4)  H vap : _ 33.3 _ kJ/mol g) (4 pts) Use your answer in f) to calculate the vapor pressure, P vap , of benzene at 450. K. 𝑙𝑛 𝑃 ଶ ൌ 𝑙𝑛 𝑃 ଵ ൅ 𝛥𝐻 vap 𝑅 ൬ 1 𝑇 ଵ െ 1 𝑇 ଶ ൰ ൌ 0 ൅ 33280 8.314 ൬ 1 353.3 െ 1 450 ൰ ൌ 2.435 𝑃 ଶ ൌ 𝑒 2.435 atm ൌ 11.4 atm +2 pts: correct equation/setup; +2 pts: correct value. (-1 pt: sig. figs <2 or >4) P vap @ 450. K: _ 11.4 _ atm +1 pt for each point/phase (=7 pts total) +1 pt for lines separating phases

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Chem 103-4 Final Exam Date last revised 12/19/2022 Page 7 of 8 PART 2 – continued (19 total pts on this page) 27. (21 pts total) Consider the following combustion reaction of propane: C 3 H 8 (g) + _ 5 _ O 2 (g) → _ 3 _ CO 2 (g) + _ 4 _ H 2 O(g) a) (3 pts) Balance this reaction. No partial credit b) (4 pts) To a bomb calorimeter with a volume of 2.75 L and a [total] heat capacity of 7.856 kJ/K you add 10.3 g of C 3 H 8 (g) and 87.0 g of O 2 (g). The temperature is 22.9 °C. What is the total pressure in the calorimeter before the combustion reaction occurs? Ideal Gas Law: PV = nRT  P = nRT/V  P = [(10.3/44.1 + 87.0/32.0) × 0.08206 × (273.15 + 22.9)]/2.75 atm = 26.08 atm +2 pts: correct equation/setup; +2 pts: correct value (-1 pt: sig. figs <2 or >4) Initial P: _ 26.1 _ atm c) (6 pts) After the combustion reaction has occurred, the calorimeter reaches a temperature of 83.3 °C. What is the heat of reaction per mole of C 3 H 8 (g)? Show all your work! 10.3 g C ଷ H ଼ ൬ 1 mol C ଷ H ଼ 44.10 g ൰ ൌ 0.2336 mol C ଷ H ଼ 87.0 g O ଶ ൬ 1 mol O ଶ 32.00 g ൰ ൌ 2.719 mol O ଶ → 2.719 mol O ଶ 0.2336 mol C ଷ H ଼ ൐ 5 +2 pts for C 3 H 8 is limiting (can also predict amount of product formed for each reactant) q rxn + q Cal = 0  q rxn = -q Cal = -C Cal ×  T Cal = -7.856 × 60.4 = -474.5 kJ ൬ െ 474.5 kJ 0.2336 mol C ଷ H ଼ ൰ ൌ െ 2032 kJ/mol C ଷ H ଼ +2 pts: correct equation/setup; +2 pts: correct value. (-1 pt: sig. figs <2 or >4) q rxn : _ -2030 _ kJ/mol C 3 H 8 d) (4 pts) Now, estimate  H for this combustion reaction by using bond enthalpies: C–H: 416 kJ/mol; C–C: 356 kJ/mol; O=O: 498 kJ/mol; C=O: 803 kJ/mol; O–H: 467 kJ/mol Bonds broken: 2 × C-C + 8 × C-H + 5 × O=O = 6530 kJ/mol Bonds formed: 6 × C=O + 8 × O-H = 8554 kJ/mol +2 pts: bonds broken; +2 pts: bonds formed. (-1 pt: wrong sign; -1pt: sig. figs <2 or >4)  H : _- 2020 _ kJ/mol C 3 H 8 e) (4 pts) Explain briefly the values you obtained in parts c) and d) only provide estimates of the true enthalpy of reaction,  H ? The value obtained in c) corresponds to the change in internal energy, not enthalpy because the measurement was carried out under constant volume conditions. The value obtained in d) relies on average bond enthalpies determined for a diverse set of compounds; the values are not specific to the reaction of interest. +2 pts for each. Words underlined must be present.

Chem 103-4 Final Exam Date last revised 12/19/2022 Page 8 of 8 PART 2 – continued (25 total pts on this page) 28. (12 pts) To an insulated beaker containing 175 g of water at 55.5 °C, you add a piece of hot iron (mass of 153 g) at 855 °C. The specific heat capacities of iron and H 2 O(l) are 0.449 J/g  K and 4.184 J/g  K, respectively and the heat of vaporization of water is 2260 J/g. a) (4 pts) What is the intermediate temperature of the iron when the water starts boiling? 0 = C Iron × m Iron ×  T Iron + C water × m water ×  T water   T Iron = -(  C water × m water ×  T water )/(C Iron × m Iron ) = -(4.184×175×44.5)/(0.449×153) K=-474 K +2 pts: correct equation/setup; +2 pts: correct value. (-1 pt: sig. figs <2 or >4) Intermediate temperature of iron: _ 381 _ °C b) (8 pts) What is the final temperature of the iron and how much H 2 O(l) is left, if any, after equilibrium has been reached? 0 = C Iron × m Iron ×  T2 Iron + m water ×  H vap  m(H 2 O) needed to evaporate for iron to cool to 100 °C: m water = -(C Iron × m Iron ×  T2 Iron )/  H vap m water = -[0.449 × 153 × (-281)]/2260 g = 8.53 g  remaining H 2 O(l): 175 – 8.53 g = 166 g +4 pts : correct equation/setup; +2 pts: correct mass of water that will evaporate. +1 pt: correct mass of remaining H 2 O; +1 pt: correct final Final T of iron: _ 100. _ °C Mass of remaining H 2 O(l): _ 166 _ g 29. (8 pts total) Superconductors represent an important class of solid-state materials. The first material ever discovered to become superconducting above the boiling point of liquid nitrogen is yttrium barium copper oxide . Determine the composition of this superconductor on the basis of the single unit cell shown on the right. Y: _ 1 _ Ba: _ 2 _ Cu: _ 3 _ O: _ 7 _ +2 pts for each correct value 30. (8 pts) A metal with a density of 7.874 g/cm 3 crystallizes with a body-centered cubic unit cell with a unit cell edge length of 286.7 pm. What is the element? Show your work! 𝑑 ൌ 𝑚 𝑉 ൌ 2 ൈ 𝑀ሺ𝑋ሻ 𝑁 ஺ ൈ 𝑎 ଷ → 𝑀ሺ𝑋ሻ ൌ 𝑑 ൈ 𝑁 ஺ ൈ 𝑎 ଷ 2 ൌ 7.874 ൈ 6.022 ൈ 10 23 ൈ ሺ 286.7 ൈ 10 ିଵ଴ ሻ ଷ 2 g/mol ൌ 55.87 g/mol +4 pts : correct equation/setup; can give partial credit if setup is partially correct. +2 pts: correct molar; +2 pts: correct element Element: _ Fe _