General Chemistry I Final Exam 100 pts Fall 2010

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General Chemistry I Final Exam 100 pts Fall 2010 Name This is a closed-book exam: the only reference materials you may use are a periodic table of the elements, a table of enthalpies of formation,

1 General Chemistry I Final Exam 100 pts Fall 2010 Name This is a closed-book exam: the only reference materials you may use are a periodic table of the elements, a table of enthalpies of formation, and a table of bond energies. There is a 3-hour time limit for taking the exam. The exam has four parts: 1. Short answer 2. Long answer 3. Multiple choice 4. Extra-credit Handy reference material: The molar volume of an ideal gas is 22.4 L at STP 1J = calorie R = atm L mol K E k = 1 2 mass x speed 2 E = hc λ h = x J s 1 nm = 10-9 m Short Answer 2.5 pts each Answer 12 of the following questions 1. Describe the difference between intensive and extensive properties. Which of the following properties are intensive?: a. Mass b. Density c. Volume d. Melting point 1

2 2. What s the difference between thermal energy and temperature? Does 1 L of water at 65 F have more, less, or the same quantity of thermal energy as 1 L of water at 65 C? 3. What is the key difference between an element and a compound? 4. State the mass law or laws demonstrated by the following experimental result: a student heats 1.27 g of copper and 3.50 g of iodine to produce 3.81 g of a white compound, and 0.96 g of iodine remains. 5. The atomic mass of an atom of each element is given relative to the mass of one 12 C atom. If a 12 C atom has 6 protons and 6 neutrons why are all of the atomic masses in the periodic table fractional? E.g, Mg = 24.3 amu, not 24.0 amu. 6. Are molecules present in a sample of KCl? Please explain. 7. Write an empirical formula for each of the following: N 2 H 4 and C 6 H 12 O 6. 2

3 8. How many moles of carbon atoms are there in one mole of sucrose (C 12 H 22 O 11 )? 9. Calculate the molar mass of each of the following: a. C 8 H 10 b. MgSO 4 7H 2 O c. Ca(C 2 H 3 O 2 ) Calculate each of the following quantities: a. mass in grams of 0.64 mol of MnSO 4 b. number of N atoms in 92.6 g of NH 4 NO Does a solution of each of the following substances conduct an electric current? a. sodium hydroxide b. glucose (C 6 H 12 O 6 ) 12. Nitric acid is a very strong acid. What is the molarity of H + (aq) in a 1.4 M solution of nitric acid (HNO 3 )? 13. Use Lewis dot notation to show the valence electrons for an atom of each of the following elements: C, O, S, Ar 3

4 14. Draw the partial (valence-level) orbital diagram, and write the symbol, group number, and period number of the element: a. [Ne]3s 2 3p 5 b. [Ar]4s 2 3d 10 4p 3 Long Answer 5 pts each Answer 12 of the following questions 1. A sample of sulfur hexafluoride gas occupies a volume of 5.10 L at 198 C. Assume that the pressure remains constant: what temperature (in K) is needed to reduce the volume to 2.50 L? 2. How many unpaired electrons are present in the ground state of an atom from each of the following groups? Draw a valence-level orbital diagram to illustrate your answer: a. 2A(2) b. 5A(15) c. 8A(18) 3. What is the abbreviation for each of the following, and what feature of an orbital is related to each: a. principle quantum number b. magnetic quantum number c. angular momentum quantum number d. Also, what does the quantum number m s denote? 4

5 4. Balance the following equation, and calculate ΔH rxn for the reaction: a. H 2 S(g) + O 2 (g) SO 2 (g) + H 2 O(g) 5. Calculate the enthalpy change for the reaction NO(g) + O(g) NO 2 (g) from the following data: NO(g) + O 3 (g) NO 2 (g) + O 2 (g) O 3 (g) 1.5O 2 (g) O 2 (g) 2O(g) ΔH = kj ΔH = kj ΔH = kj 5

6 6. Sucrose (aka table sugar, C 12 H 22 O 11 ) is oxidized in our bodies through a series of enzyme-mediated reactions that ultimately produce CO 2 (g) and H 2 O(l) and releases 5.64 x 10 3 kj/mol sucrose. How much thermal energy is released per gram of sucrose oxidized? 7. Calculate the ΔH rxn for the decomposition of calcium carbonate to calcium oxide and carbon dioxide: CaCO 3 (s) CaO(s) + CO 2 (g) ΔH f [CaCO 3 (s)] = kj/mol ΔH f [CaO(s)] = kj/mol ΔH f [CO 2 (g)] = kj/mol 6

7 8. Use the following (balanced?) reaction to determine how many grams of ethanol are produced from the decomposition of 10.0 g of glucose (the reaction is run at standard temperature and pressure). a. C 6 H 12 O 6(s) -- (yeast )-- CO 2(g) + C 2 H 5 OH (l) 9. Consider the article Alien life? NASA-funded study questioned [available at the Courses with this exam]. Do you think it s better to quickly push news of interesting findings into the public domain, or to share new work through a slower, more deliberate peer-review process? Please explain your answer. 7

8 10. The graph below shows the distribution of molecular speeds for argon and helium at the same temperature. Does curve 1 or curve 2 better represent the behavior of argon? Please explain your answer Draw approximate enthalpy diagrams for a) the combustion of 1 mol of methane and b) for the freezing of liquid water. 8

9 12. Aluminum reacts with hydrochloric acid to form aqueous aluminum chloride and 35.8 ml of hydrogen gas over water at 27 C and 751 mmhg. How many grams of aluminum reacted? 13. Fluorescent lamps emit sharp lines in the visible regions from a mercury discharge within the tube. Much of this light has a wavelength of 436 nm. What is the energy, in J, of one photon of this light? 9

10 14. Based on their electron configuration, which of the following elements has the smallest first ionization energy, and why? Rb, Mg, I, As, or F 15. Why does a covalent bond form e.g., H 2, or H-H and why must energy be applied to break a covalent bond? 10

11 Multiple choice 10 pts 1. Which of the following must be the same before and after a chemical reaction? (a) The sum of the masses of all substances involved. (b) The number of molecules of all substances involved. (c) The number of atoms of each type involved. (d) Both (a) and (c) must be the same. (e) Each of the answers (a), (b), and (c) must be the same. 2. What is the mass of the solution when 1 pound of salt is dissolved in 20 pounds of water? (a) 19 Pounds. (b) 20 Pounds. (c) Between 20 and 21 pounds. (d) 21 pounds. (e) More than 21 pounds. 3. True or False? When a match burns, some matter is destroyed. (a) True (b) False 4. What is the reason for your answer to question 3? (a) This chemical reaction destroys matter. (b) Matter is consumed by the flame. (c) The mass of ash is less than the match it came from. (d) The atoms are not destroyed, they are only rearranged. (e) The match weighs less after burning. 5. A 1.0-gram sample of solid iodine is placed in a tube and the tube is sealed after all of the air is removed. The tube and the solid iodine together weigh 27.0 grams. The tube is then heated until all of the iodine evaporates and the tube is filled with iodine gas. The weight after heating be: (a) less than 26.0 grams. (b) 26.0 grams. (c) 27.0 grams. (d) 28.0 grams. (e) more than 28.0 grams. 6. What is the reason for your answer to question 5? (a) A gas weighs less than a solid. (b) Mass is conserved. (c) Iodine gas is less dense than solid iodine. (d) Gasses rise. (e) Iodine gas is lighter than air. 11

12 ml of water at 25 C and 100 ml of alcohol at 25 C are both heated at the same rate under identical conditions. After 3 minutes the temperature of the alcohol is 50 C. Two minutes later the temperature of the water is 50 C. Which liquid received more heat as it warmed to 50 C? (a) The water. (b) The alcohol. (c) Both received the same amount of heat. (d) It is impossible to tell from the information given. 8. What is the reason for your answer to question 7? (a) Water has a higher boiling point then the alcohol. (b) Water takes longer to change its temperature than the alcohol. (c) Both increased their temperatures 25_ C. (d) Alcohol has a lower density and vapor pressure. (e) Alcohol has a higher specific heat so it heats faster. 9. Iron combines with oxygen and water from the air to form rust. If an iron nail were allowed to rust completely, one should find that the resulting rust weighs: (a) less than the nail it came from. (b) the same as the nail it came from. (c) more than the nail it came from. (d) It is impossible to predict. 10. What is the reason for your answer to question 9? (a) Rusting makes the nail lighter. (b) Rust contains iron and oxygen. (c) The nail flakes away. (d) The iron from the nail is destroyed. (e) The flaky rust weighs less than iron. Extra credit, 5 pts. Write a Lewis dot structure for sulfuric acid, H 2 SO 4 12

CHEM 101 Fall 09 Final Exam (a)

CHEM 101 Fall 09 Final Exam (a) On the answer sheet (scantron) write your name, student ID number, and recitation section number. Choose the best (most correct) answer for each question and enter it on