Exam 1 Fall 2023 KEY

pdf

School

University of Wisconsin, Madison *

*We aren’t endorsed by this school

Course

103

Subject

Chemistry

Date

Jan 9, 2024

Type

pdf

Pages

Uploaded by KidField12546

Chem 103 MWF Exam 1 Date last revised 10/8/2023 Page 1 of 10 CHEMISTRY 103 MWF Name _________________________________ EXAM 1 October 4, 2023 Disc _________ TA ______________________ INSTRUCTIONS: 1. Do not separate the pages of the exam. 2. PRINT your name, 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 under “Special Codes”. 1 = Zelewski 8:50 AM 2 = Zelewski 11:00 AM 3 = Zhou 1:20 PM 4 = Brunold 3:30 PM 4. Write your answers to the multiple choice questions in this test booklet so you have a record of what your answer is, 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 75 minutes. 7. When you are finished, turn in your notecard, reference sheet, 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 13 _________/14 question 14 _________/13 question 15 _________/9 question 16 _________/16 _________/52 Short Answer Total KEY

Chem 103 MWF Exam 1 Date last revised 10/8/2023 Page 2 of 10 Enter your answers to the following questions on the scantron form. Each question is worth 4 points. There is ONE best response to each question. 1. An atom of an unknown element X has a mass of 64 amu and 34 neutrons. What element is X? A. Se B. Zn C. Ga D. Gd E. Tb 2. Consider the following four compounds: CoCl 2 N 2 O 4 OCl 2 CaO How many of these are molecular compounds? A. 0 B. 1 C. 2 D. 3 E. 4 3. Which of the following pairs of substances will react with each other when they are combined? (i) FeCl 2 (aq) and K(s) (ii) NiSO 4 (aq) and Ag(s) (iii) AgNO 3 (aq) and Sn(s) A. Only (ii) B. Only (iii) C. Only (i) and (ii) D. Only (ii) and (iii) E. Only (i) and (iii) 4. The following diagram represents the collection of CO 2 and H 2 O molecules formed by the complete combustion of a hydrocarbon. What is the empirical formula of the hydrocarbon? A. CH B. CH 2 C. CH 3 D. C 4 H 6 E. C 4 H 12

Chem 103 MWF Exam 1 Date last revised 10/8/2023 Page 3 of 10 5. The graph below shows the numbers of neutrons versus number of protons for stable isotopes of the elements. Which of the following statements regarding this graph is FALSE ? A. This graph includes elements from period 4. B. The element with 39 protons has a stable isotope with 50 neutrons. C. This graph shows that stable isotopes tend to have more neutrons than protons. D. This graph allows us to predict the exact number of stable isotopes the element with 60 protons would have. E. The average atomic mass of elements with 30-50 protons cannot be determined from the data presented in the graph alone. 6. An area of 300 μm 2 (micrometer squared) is equal to _____ mm 2 (millimeter squared) A. 0.000003 B. 0.0003 C. 0.3 D. 300,000 E. 300,000,000 7. Which of the following statements is FALSE given the following net ionic equation? H 3 PO 4 (aq) + 3 OH – (aq) → PO 4 3– (aq) + 3 H 2 O( ℓ ) A. If all the water was evaporated, the salt remaining could possibly be Na 3 PO 4 . B. The acid, H 3 PO 4 , is a weak electrolyte. C. The cation, K + , could possibly be a spectator ion. D. This is classified as a neutralization reaction. E. This could be the net ionic equation for H 3 PO 4 reacting with Al(OH) 3 . 15 20 25 30 35 40 45 50 55 60 15 25 35 45 55 65 75 85 Number of Neutrons Number of Protons Stable Isotopes of the Elements

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version

Access to all documents
Unlimited textbook solutions
24/7 expert homework help

Chem 103 MWF Exam 1 Date last revised 10/8/2023 Page 4 of 10 8. Given 1 mole of each of the compounds listed below, which compound will have the greatest number of ions? A. AlCl 3 B. KMnO 4 C. NH 4 CH 3 COO D. Mg(ClO 4 ) 2 E. Li 2 CO 3 9. Potassium iodate, KIO 3 , is an ionic compound that contains the iodate polyatomic ion. What is the chemical formula of the iodate ion? A. O 2– B. O 3 C. O 3 – D. IO 3 – E. IO 3 2– 10. CH 3 COOH is a(n) ___. A. ionic compound that partially ionizes in water to form a small number of H 3 O + and CH 3 COO – ions. B. ionic compound that completely ionizes in water to form H 3 O + and CH 3 COO – ions. C. molecular compound that does not form any ions when added to water. D. molecular compound that partially ionizes in water to form a small number of H 3 O + and CH 3 COO – ions. E. molecular compound that completely ionizes in water to form H 3 O + and CH 3 COO – ions. 11. Consider the reaction: 2 NaI(aq) + 2 H 2 SO 4 (aq) + MnO 2 (s) → Na 2 SO 4 (aq) + MnSO 4 (aq) + I 2 (s) + 2 H 2 O( ℓ ). Which of the following statements is correct ? A. I – is oxidized and MnO 2 is the oxidizing agent. B. I – is oxidized and NaI is the oxidizing agent. C. Mn 4+ is oxidized and NaI is the oxidizing agent. D. Mn 4+ is oxidized and MnO 2 is the oxidizing agent. E. O 2– is oxidized and H 2 SO 4 is the oxidizing agent. 12. Determine the moles of Fe(s) that can be produced from the reaction of 12.3 mol Fe 2 O 3 (s) with 29.6 mol CO(g): Fe 2 O 3 (s) + 3 CO(g) → 2 Fe(s) + 3 CO 2 (g) A. 12.3 mol B. 19.7 mol C. 24.6 mol D. 29.6 mol E. 41.9 mol Make sure to enter your multiple choice answers on the scantron form!

Chem 103 MWF Exam 1 Date last revised 10/8/2023 Page 5 of 10 Answer the following questions directly in the space provided in this exam. Show all relevant work to receive full credit. 13. [14 points total] Reaction Types and Chemical Logic A. [6 pts] Fill in the table by writing what you would observe when the two aqueous solutions are mixed together. Use the following abbreviations: ppt = precipitate is formed gas = gas is formed NOC = No Observable Change Solutions HBr Cd(NO 3 ) 2 KOH Li 2 CO 3 HBr NOC NOC gas Cd(NO 3 ) 2 NOC ppt ppt KOH NOC ppt NOC Li 2 CO 3 gas ppt NOC +1 pt each correct observation B. [4 pts] For each reaction in part (A) that is a gas-forming reaction, write the balanced overall chemical equation. Include states: g, ℓ , s, aq in your equation(s). Li 2 CO 3 (aq) + 2 HBr(aq) → 2 LiBr(aq) + CO 2 (g) + H 2 O( 𝓵 ) Li 2 CO 3 and HBr in reactants (+ 1 pt) Correct formula for LiBr(+1 pt), CO 2 (+1 pt) and H 2 O(+1 pt) in products –1 pt if missing or have any incorrect states –1 pt if not balanced –1 pt for each additional incorrect species in the equation –1 pt for each additional incorrect gas-forming reaction C. [4 pts] For each reaction in part (A) that is a precipitation reaction, write the balanced net ionic equation. Include states: g, ℓ , s, aq in your equation(s). Cd 2+ (aq) + 2 OH – (aq) → Cd(OH) 2 (s) Cd 2+ (aq) + CO 3 2– (aq) → CdCO 3 (s) Each equation is worth 2 pts: +1 pt for correct formula of product +1 pt for balanced net ionic equation, including states, for correct product –1 pt for each additional incorrect precipitation reaction _____ /14 pts ____/6 pts ____/4 pts ____/4 pts

Chem 103 MWF Exam 1 Date last revised 10/8/2023 Page 6 of 10 14. [13 points total] Three potential energy vs ion distance curves (A, B, C) are shown in the graph below. The melting points of three unknown ionic compounds (X, Y, Z) are listed in the table below. A. [3 pts] Which curve corresponds to which ionic compound? (+1 pt for each correct answer) Compound X corresponds to Curve ___ B ___ Compound Y corresponds to Curve ___ A ___ Compound Z corresponds to Curve ___ C ___ B. [4 pts] What feature(s) of the potential energy curve allow you to answer part (A)? Briefly explain your answer. The minimum potential energy, U min , of each curve (+2 pts) (–1 pt if include distance between ions) A lower U min (or a larger |U min |) corresponds to a higher melting point. (+2 pts) C. [3 pts] The three compounds are NaCl, KBr, and Rb 2 SO 4 . Based on the information above and the provided ionic radii below, determine the identities of each unknown compound. Compound X is ___ KBr ___ Compound Y is ___ NaCl ___ Compound Z is ___ Rb 2 SO 4 ___ (+1 pt for each correct answer) D. [3 pts] Consider compound Z, whose identity you determined in part (C). Which property leads to it having the highest melting point? Circle all that apply. Briefly explain your answer. ionic radius ionic charge (+1 pt only ionic charge is circled) The higher (-2) charge of sulfate compared to (-1 charge of) bromide and chloride results in stronger attractive force/energy (and higher melting point) in Rb 2 SO 4 . (+2 pts) (Note: The larger ionic radii in Rb 2 SO 4 compared to NaCl and KBr reduces the attractive force/energy in Rb 2 SO 4 .) If in part C Z = NaCl : only ionic radius is circled in part D, +1 pt in part D; correct explanation based on ionic radii for NaCl is another +1 pt in part D. Compound Melting point (°C) X 750 Y 800 Z 1050 Ion Radius (pm) Sodium 120 Potassium 150 Rubidium (Rb) 170 Chloride 170 Bromide 180 Sulfate 250 ____/3 pts ____/4 pts ____/3 pts ____/3 pts _____ /13 pts

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version

Access to all documents
Unlimited textbook solutions
24/7 expert homework help

Chem 103 MWF Exam 1 Date last revised 10/8/2023 Page 7 of 10 15. [9 points total] Solid aluminum chloride can be prepared by treating aluminum metal with chlorine gas according to the balanced chemical reaction shown below. 2 Al(s) + 3 Cl 2 (g) → 2 AlCl 3 (s) A. [6 pts] When 6.40 g of Al(s) (26.98 g/mol) react with 16.15 g of Cl 2 (g) (70.91 g/mol), what is the theoretical yield (in grams) of aluminum chloride (133.34 g/mol)? Show your work. ሺ 6.40 g Al ሻ ൬ 1 mol Al 26.98 g Al ൰ ൬ 2 mol AlCl ଷ 2 mol Al ൰ ൌ 0.237 mol AlCl ଷ ሺ 16.15 g Cl ଶ ሻ ൬ 1 mol Cl ଶ 70.91 g Cl ଶ ൰ ൬ 2 mol AlCl ଷ 3 mol Cl ଶ ൰ ൌ 0.1518 mol AlCl ଷ ⟶ limiting reagent is Cl ଶ ሺ 0.1518 mol AlCl ଷ ሻ ൬ 133.34 g AlCl ଷ 1 mol AlCl ଷ ൰ ൌ 20.24 g AlCl ଷ 𝐎𝐑 ሺ 6.40 g Al ሻ ൬ 1 mol Al 26.98 g Al ൰ ൬ 2 mol AlCl ଷ 2 mol Al ൰ ൬ 133.34 g AlCl ଷ 1 mol AlCl ଷ ൰ ൌ 31.63 g AlCl ଷ ሺ 16.15 g Cl ଶ ሻ ൬ 1 mol Cl ଶ 70.91 g Cl ଶ ൰ ൬ 2 mol AlCl ଷ 3 mol Cl ଶ ൰ ൬ 133.34 g AlCl ଷ 1 mol AlCl ଷ ൰ ൌ 𝟐𝟎 . 𝟐𝟒 𝐠 𝐀𝐥𝐂𝐥 𝟑 ⟶ limiting reagent is Cl ଶ +4 pts: Correct identification of limiting reagent with work clearly showing how it is determined +2 pts: Correct calculation of mass of AlCl 3 product –1 pt for <3 or >5 significant figures for mass of AlCl 3 Theoretical yield: _ 20.24 _ grams ____/6 pts B. [3 pts] What mass of the excess reactant in part (A) remains at the end of the reaction? Show your work. Al consumed: ሺ 0.1518 mol AlCl ଷ ሻ ൬ 2 mol Al 2 mol AlCl ଷ ൰ ൬ 26.98 g 1 mol Al ൰ ൌ 4.096 g Al 𝐎𝐑 ሺ 16.15 g Cl ଶ ሻ ൬ 1 mol Cl ଶ 70.91 g Cl ଶ ൰ ൬ 2 mol Al 3 mol Cl ଶ ൰ ൬ 26.98 g 1 mol Al ൰ ൌ 4.096 g Al Al remaining: 6.40 g െ 4.096 g ൌ 𝟐 . 𝟑𝟎 𝐠 𝐀𝐥 𝐎𝐑 via conservation of mass: ሺ 6.40 g ൅ 16.15 g ሻ െ 20.24 g ൌ 𝟐 . 𝟑𝟏 𝐠 𝐀𝐥 remains +2 pts: Correct calculation for mass of Al consumed +1 pt: Correct calculation for mass of Al remaining –1 pt for <2 or >4 significant figures for mass of Al Mass of excess reactant: _ 2.30 _ grams ____/3 pts _____ /9 pts

Chem 103 MWF Exam 1 Date last revised 10/8/2023 Page 8 of 10 16. [16 points total] When 7.288 g of a compound that only contains carbon , hydrogen , and bromine are burned completely in excess O 2 (g), 6.056 g of CO 2 (g) (44.01 g/mol) and 1.240 g of H 2 O(g) (18.02 g/mol) are produced, along with some bromine oxides. A. [8 pts] What is the empirical formula of this compound? Show your work. Unbalanced equation: C x H y Br z + O 2 (g) → CO 2 (g) + H 2 O(g) + Bromine oxides ሺ 6.056 g CO ଶ ሻ ൬ 1 mol CO ଶ 44.01 g CO ଶ ൰ ൬ 1 mol C 1 mol CO ଶ ൰ ൌ 0.1376 mol C ൅ 1 pt correct calc for mol C ሺ 0.1376 mol C ሻ ൬ 12.01 g C 1 mol C ൰ ൌ 1.653 g C ൅ 1 pt correct calc for g C ሺ 1.240 g H ଶ O ሻ ൬ 1 mol H ଶ O 18.02 g H ଶ O ൰ ൬ 2 mol H 1 mol H ଶ O ൰ ൌ 0.1376 mol H ൅ 1 pt correct calc for mol H ሺ 0.1376 mol H ሻ ൬ 1.01 g H 1 mol H ൰ ൌ 0.139 g H ൅ 1 pt correct calc for g H The sample of C x H y Br z also contains bromine: 7.288 g sample െ 1.653 g C െ 0.139 g H ൌ 5.496 g Br ൅ 2 pts correct calc for g Br ሺ 5.496 g Br ሻ ൬ 1 mol Br 79.90 g Br ൰ ൌ 0.06879 mol Br ൅ 1 pt correct calc for mol Br 0.1376 mol H 0.06879 mol Br ൌ 2 mol H 1 mol Br 0.1376 mol C 0.06879 mol Br ൌ 2 mol C 1 mol Br Correct C:H:Br ratio and empirical formula C 2 H 2 Br +1 pt 0 pts if only an empirical formula is written and no work is shown. Empirical formula: ___ C 2 H 2 Br ___ ____/8 pts B. [1 pt] The average molar mass of this compound is 212 g/mol. What is the molecular formula of this compound? Show your work . (2 × 12.01 g/mol) + (2 × 1.01 g/mol) + 79.9 g/mol = 106, 212/106 = 2 Molecular formula: ___ C 4 H 4 Br 2 ___ ____/1 pt

Chem 103 MWF Exam 1 Date last revised 10/8/2023 Page 9 of 10 C. [4 pts] Draw the hard mass spectrum for this compound. Assume that carbon and hydrogen have a single isotope, 12 C and 1 H, and that bromine has two isotopes, 79 Br and 81 Br, each with a natural abundance of 50%. Write the relative intensity next to each signal (e.g., “5” or “3” etc.). If you are unable to identify the compound in part (B), then assume it is C 3 H 6 Br 2 . 10 20 30 40 50 60 70 m/z 80 90 1 1 4 4 0 1 2 3 4 5 6 10 20 30 40 50 60 70 m/z 80 90 1 1 4 4 0 1 2 3 4 5 6 For C 3 H 6 Br 2 10 20 30 40 50 60 70 m/z 80 90 1 1 6 3 0 1 2 3 4 5 6 +2 pts: signals at correct masses (x-axis values) +2 pts: correct relative signal intensities (relative y-axis values) Answer must be consistent with formula in part A/B, or C 3 H 6 Br 2 ____/4 pts

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version

Access to all documents
Unlimited textbook solutions
24/7 expert homework help

Chem 103 MWF Exam 1 Date last revised 10/8/2023 Page 10 of 10 D. [3 pts] Draw the soft mass spectrum for this compound. Assume that carbon and hydrogen have a single isotope, 12 C and 1 H, and that bromine has two isotopes, 79 Br and 81 Br, each with a natural abundance of 50%. Write the relative intensity next to each signal (e.g., “5” or “3” etc.). If you are unable to identify the compound in part (B), then assume it is C 3 H 6 Br 2 . 200 202 204 206 208 210 212 m/z 214 216 2 1 1 0 1 2 3 For C 3 H 6 Br 2 200 202 204 206 208 210 212 m/z 214 216 2 1 1 0 1 2 3 +2 pts: signals at correct masses (x-axis values) +1 pt: correct relative signal intensities (relative y-axis values) Answer must be consistent with formula in part B, or C 3 H 6 Br 2 _____ /16 pts ____/3 pts