Exam_3_Chem_0001_Spring_2023

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Tufts University *

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0001

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Chemistry

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Dec 6, 2023

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pdf

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12

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Midterm Exam 3: General Chemistry I with Lab, Spring 2023 Thursday, April 20, 2023, Time allowed: 60 minutes Instructions for the exam: 1. Write your Official name (as it appears on Canvas) and student ID on both the exam and the bubble sheet. 2. Multiple-choice questions will be graded based on the answers on the bubble sheet, so be sure to transfer all your answers accurately. 3. To receive full credit, show all your steps completely and clearly. 4. Use the provided solution boxes to do all your work. Name: Student ID: Grade Table : This exam consists of 19 questions Page Points Score 2 20 3 16 4 20 5 8 6 12 7 16 8 8 Total: 100
Exam 3 Multiple choice questions 1. One mole of C 12 H 22 O 11 molecules contain: [4 points] A. 12 carbon atoms B. 44 total atoms C. 12 moles of carbon atoms D. 6 . 023 10 23 carbon atoms 2. The percent water in the hydrate CuSO 4 . 6 H 2 O is: [4 points] A. 40.4% B. 6.73% C. 9.60% D. 57.6% 3. A combustion analysis of an unknown compound shows that it contains 74.0% carbon, 8.7% hydrogen, and the rest is nitrogen. What is the empirical formula of this unknown compound? [4 points] A. C 6 . 2 H 8 . 6 N 1 . 23 B. C 10 H 14 N 2 C. C 5 H 7 N D. C 6 H 9 N 4. A sample of an unknown compound has an empirical formula of CoC 4 O 4 . What is the molecular formula of the compound if its molecular mass has been experimentally determined to be 341.86 g/mol? [4 points] A. CoC 4 O 4 B. Co 2 C 4 O 4 C. Co 2 C 8 O 8 D. Co 3 C 12 O 12 5. What is the sum of the coefficients for the balanced chemical reaction that occurs when oxygen gas and hydrogen sulfide gas react to form water and gaseous sulfur dioxide? [4 points] A. 9 B. 4 C. 15 D. 5 April, 20 2023 Page 2 of 12
Exam 3 6. Calculate the volume of 18.0 M sulfuric acid that must be used to prepare 15.5 L of 0.195 M solution. [4 points] A. 92.3 mL B. 168 mL C. 0.338 L D. 1.25 L 7. Elon Musk’s SpaceX launches a new rocket and collects a rock sample from Mars. Scientists discover that there is a fixed volume of unknown gas trapped inside the rock. If 1.05 mL of the gas was extracted from the rock at STP and determined to weigh 0.188 mg, what would be the identity of the unknown gas? [4 points] A. Hydrogen B. Nitrogen C. Krypton D. Helium 8. A balloon filled with helium on a hot day (30 C) has a volume of 37 . 8 mL. What volume will the balloon occupy if the temperature drops to 25 C? [4 points] A. 37 . 8 mL × ( 298 K 303 K ) B. 37 . 8 mL × ( 303 K 298 K ) C. 37 . 8 mL × ( 30 C 25 C ) D. 37 . 8 mL × ( 25 C 30 C ) (This text is for questions 9-11) A group of students measured the time it takes for different compounds to diffuse across a room that was about 20 meters wide. They made the measurements on different days and recorded the following data: Day Temperature Time to other side (sample 1) Time to other side (sample 2) 1 300K 52 sec 96 sec 9. The molar mass ratio of sample 1 / sample 2 is: [4 points] A. 96 / 52 B. 52 / 96 C. (52 / 96) 2 D. p 52 / 96 April, 20 2023 Page 3 of 12
Exam 3 10. If the students measured the time of diffusion on a very cold day (273 K), the molar mass ratio of sample 1 / sample 2 would [4 points] A. stays the same B. decrease because the particles are moving slower C. decrease because the lighter particles move faster D. increase because the heavier particles move faster 11. The best estimate of the time it would take sample 1 to diffuse to the other side of the room on the cold day (T=273 K), is [4 points] A. 49 sec B. 52 sec C. 55 sec D. 57 sec 12. Nitrogen will behave most like an ideal gas [4 points] A. at high temperature and low pressure. B. at low temperature and high pressure. C. at intermediate (moderate) temperature and pressure. D. at low temperature and low pressure. E. at high temperature and high pressure. 13. A solution of potassium hydroxide is mixed with chromium (III) nitrate. The balanced net ionic equation for the reaction occurring in the container is: [4 points] A. Cr 2+ (aq) + 2OH (aq) Cr(OH) 2 (s) B. Cr 3+ (aq) + 3OH (aq) Cr(OH) 3 (s) C. Cr(NO 3 ) 3 (aq) + 3KOH (aq) 3KNO 3 (aq) + Cr(OH) 3 (s) D. Cr 3+ (aq) + 3NO 3 (aq) + 3K + (aq) + 3OH (aq) 3K + (aq) + 3NO 3 (aq) + Cr(OH) 3 (s) 14. Which of the following is an oxidation-reduction reaction? [4 points] A. Cu (s) + 2AgNO 3 (aq) 2Ag (s) + Cu(NO 3 ) 2 (aq) B. HCl (aq) + NaOH (aq) H 2 O (l) + NaCl (aq) C. AgNO 3 (aq) + HCl (aq) AgCl (s) + HNO 3 (aq) D. Ba(C 2 H 3 O 2 ) 2 (aq) + Na 2 SO 4 (aq) BaSO 4 (s) + 2NaC 2 H 3 O 2 (aq) E. H 2 CO 3 (aq) + Ca(NO 3 ) 2 (aq) 2HNO 3 (aq) + CaCO 3 (s) April, 20 2023 Page 4 of 12
Exam 3 15. Select the best statement relating to the following reaction: [4 points] 2 MnO 2 (s) + KClO 3 (aq) + 2 KOH(aq) 2 KMnO 4 (aq) + KCl(aq) + H 2 O(l) A. K in KClO 3 is the reducing agent. B. H in KOH is oxidized. C. Cl in KClO 3 is the reducing agent. D. O in KClO 3 is the oxidizing agent. E. Mn in MnO 2 is oxidized. 16. Based on the activity series, which one of the reactions below will occur? [4 points] A. Fe (s) + ZnCl 2 (aq) FeCl 2 (aq) + Zn (s) B. Mn (s) + NiCl 2 (aq) MnCl 2 (aq) + Ni (s) C. Pb (s) + NiI 2 (aq) PbI 2 (aq) + Ni (s) D. SnBr 2 (aq) + Cu (s) CuBr 2 (aq) + Sn (s) E. None of the reactions will occur. April, 20 2023 Page 5 of 12
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