CHEMISTRY 107 Section 501 Exam #1 Version A September 22, 2017 Dr. Larry Brown

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1 NAME: (print) UIN #: CHEMISTRY 107 Section 501 Exam #1 Version A September 22, 2017 Dr. Larry Brown This is a 50-minute exam, and contains 14 multiple choice questions and 4 free response problems. Point values for the different questions are as indicated. There should be 10 numbered pages, including this one. Page 10 is blank and can be used for scratch work if needed. There is also a periodic table attached to the back of the exam; you may tear the periodic table page off, and you do not need to turn that page in. Questions 1 14 should be answered on the scantron provided to you. Problems should be answered on the exam paper, with ALL of your work shown as clearly as possible. This will help us award partial credit. Answers without supporting work may not receive credit. You may use a calculator for this exam, but you may NOT retrieve or use any alphanumeric information or algorithms that might be stored in your calculator s memory. Please PRINT your name and UIN number above, and SIGN the honor code statement below. Also, please put your name on every page of the exam, in case a page gets detached from the exam. Potentially Useful Information PHYSICAL CONSTANTS Avogadro s Number N A = mol 1 CONVERSION FACTORS 1 amu = g 1 kg = 1,000 g 1 µg = 10 6 g 1 L = 1,000 ml 1 cm = 10 2 m 1 mm = 10 3 m 1 km = 10 3 m "On my honor, as an Aggie, I have neither given nor received unauthorized aid on this exam." SIGNATURE: PLEASE DO NOT OPEN YOUR EXAM UNTIL TOLD TO DO SO. Exam 2017 L.S. Brown A1

2 (3 pts) 1. An atom of a particular isotope contains 14 protons and 16 neutrons. What is the correct chemical symbol for this isotope? (Remember that you have a periodic table available.) (A) 30 S (B) 30 Si (C) 14 O (D) 16 Si (E) 14 S (3 pts) 2. How many of the five properties listed below must be the same on both sides of a properly balanced chemical equation? (i). Total number of atoms (ii). Number of atoms of each element (iii). Number of molecules (iv). Total mass (v). Electric charge (A) 1 (B) 2 (C) 3 (D) 4 (E) 5 (3 pts) 3. Given that the formula for the ionic compound potassium dichromate is K 2 Cr 2 O 7, what is the charge on a dichromate ion? (A) 2+ (B) 1+ (C) 0 (D) 1 (E) 2 (3 pts) 4. Which one of the following compounds acts as a weak base in aqueous solution? (A) NaOH (B) HCl (C) CH 3 COOH (D) NH 3 (E) NaCl (5 pts) 5. The compound shown below is eugenol, which is often used as a flavoring agent in pumpkin spice blends. What is its correct molecular formula? HO O (A) C 9 H 10 O 2 (B) C 10 H 16 O 2 (C) C 10 H 12 O 2 (D) C 11 H 14 O 2 (E) C 10 H 10 O 2 A L.S. Brown

3 NAME: (5 pts) 6. Pyridine (C 5 H 5 N) reacts with oxygen to produce CO 2, H 2 O, and N 2. Write a properly balanced chemical equation for this reaction. What is the sum of all of the stoichiometric coefficients in the balanced equation? (If your equation includes any coefficients of one, be sure to count those.) (A) 53 (B) 61 (C) 46 (D) 33 (E) 18 (5 pts) 7. How many hydrogen atoms are in 8.5 g of ammonia, NH 3? (A) (B) (C) (D) (E) (5 pts) 8. What is the concentration of nitrate ions in a solution labeled as M Fe(NO 3 ) 3? (A) M (B) M (C) M (D) M (E) None of those 2017 L.S. Brown A3

4 (6 pts) 9. A solution is prepared by dissolving g of MgCl 2 in enough water to give ml of solution. What is the molarity of MgCl 2 in this solution? (A) M (B) M (C) M (D) M (E) M (6 pts) 10. Concentrated hydrochloric acid is a 12.1 M solution. What volume of hydrochloric acid should be used to prepare 275 ml of M HCl? (A) 5.11 ml (B) 181 ml (C) 5.45 ml (D) 2.84 ml (E) 352 ml (6 pts) 11. Limestone (calcium carbonate, CaCO 3 ) dissolves in hydrochloric acid as shown in the equation below. What is the minimum volume of 4.00 M HCl required to dissolve 2.50 kg of calcium carbonate? CaCO 3 (s) + 2 HCl(aq) H 2 O(l) + CO 2 (g) + CaCl 2 (A) 12.5 L (B) 37.5 L (C) 638 ml (D) 33.3 L (E) 6.24 L A L.S. Brown

5 NAME: The drawing below shows a molecular scale representation of the products of a reaction between N 2 and O 2 molecules. Use this drawing to answer questions 12, 13, and 14. = N = O (4 pts) 12. Which of the following drawings shows the combination of reactants that must have been present before the reaction occurred? (A) (B) (C) (D) (E) (4 pts) 13. What is the sum of all of the coefficients in a properly balanced chemical equation for the reaction? (A) 3 (B) 7 (C) 13 (D) 14 (E) 16 (4 pts) 14. What was the limiting reactant in the reaction? (A) N 2 (B) N 2 O 3 (C) O 2 (D) N 2 O 2 (E) There was no limiting reactant 2017 L.S. Brown A5

6 (8 pts) 15. Oil spreads on water to form a film about 90 nm thick. How many square miles of ocean would be covered by an oil slick resulting from the spill of a single 42-gallon barrel of oil? (In addition to the conversion factors listed below, you can find more on the front page of the exam. Show ALL of your work clearly; do not use any unit conversion functions that may be available on your calculator.) 1 gallon = L 1 L = 10 3 m 3 1 mile = km 1 m = 10 9 nm A L.S. Brown

7 NAME: (10 pts) 16. A compound called apigenin is found in parsley and celery. It contains 66.67% carbon, 3.73% hydrogen, and 29.60% oxygen by mass. If one molecule of apigenin has a mass of g, what is the molecular formula for this compound? 2017 L.S. Brown A7

8 (10 pts) 17. The Draco thruster rockets on SpaceX s Dragon spacecraft are based on the following reaction between monomethylhydrazine (CH 6 N 2 ) and dinitrogen tetroxide (N 2 O 4 ): 4 CH 6 N 2 (l) + 5 N 2 O 4 (l) 12 H 2 O(l) + 4 CO 2 (g) + 9 N 2 (g) This is an example of what is called a hypergolic fuel mixture, which means it ignites immediately when the two components come into contact with one another. A fuel mixture comprising g of CH 6 N 2 and g of N 2 O 4 is used in a test of a laboratory-scale mock-up of the Draco thruster. When the engine stops burning, some unused fuel remains. What substance is this unburned fuel, and what mass of it should be found? Molar masses of the substances involved in the reaction are as follows: CH 6 N 2 : g/mol N 2 O 4 : g/mol H 2 O: g/mol CO 2 : g/mol N 2 : g/mol A L.S. Brown

9 NAME: (10 pts) 18. When a piece of copper metal is dipped into a solution of silver nitrate, the copper begins to dissolve and silver metal forms on the surface of the copper. The molecular equation for this reaction is: 2 AgNO 3 (aq) + Cu(s) Cu(NO 3 ) 2 (aq) + 2 Ag(s) In one experiment, a 2.00-g strip of copper is placed in an AgNO 3 solution for a short time. The strip, now containing both copper and silver, is then removed from the solution, dried, and weighed. If the final mass is 4.18 g, what mass of copper remains in the strip at the end of this experiment? (HINT: Remember that copper is being dissolved from the strip as the silver metal forms, as seen in the reaction above.) 2017 L.S. Brown A9

CHEMISTRY 107 Section 501 Mini-Exam Version A September 7, 2018 Dr. Larry Brown

NAME: (print) KEY UIN #: CHEMISTRY 107 Section 501 Mini-Exam Version A September 7, 2018 Dr. Larry Brown This is a 25-minute exam, and contains 12 multiple choice questions. Point values for the different