Chemistry 200: General Chemistry I - Lecture

Transcription

1 Name Date Chemistry 200: General Chemistry I - Lecture Exam #3, 100 Points Total Form: A Read all directions carefully. Answers not conforming to the directions will be marked as incorrect! Section 1: Matching (10 points) Match the following concepts with the appropriate definitions or examples listed below. Make selections such that each term has its best possible match. Indicate your choices by marking your Scantron sheet (1-10) with the appropriate two-letter code. actual yield spectator ions reducing agent chemical change mole ratios 1st Law of Thermodynamics titration complete ionic equation Avogadro s Law calorimetry BE. procedure to find unknown concentration using a known concentration CD. based on q system = q surroundings AE. lists all of the ions present on reactant and product sides BC. do not participate in a reaction AD. limited by side reactions and lab skills BD. the substance that undergoes oxidation AC. conversion factors obtained from balanced equations AB. when atoms rearrange into a new substance CE. E universe = E system + E surroundings DE. more n gas requires more V 1

2 Section 2: Multiple Choice (40 points) Choose the term or phrase that best completes the sentence or answers the question. Indicate your selection by marking the appropriate letter on your Scantron sheet. 11. Which of the following would be the strongest electrolyte? LiBr CO CdS Cu 12. Which of the following terms would be incorrect for the specific Born-Haber equation for FeCl 3? H IE3,Fe 3 H EA1,Cl 3 H BE,Cl 2 H Sub,Fe 13. is used to determine the theoretical yield. Stoichiometry Weighing Percent yield Precipitation 14. Which enthalpy is most appropriate for the reaction H 2 O (l) H 2(g) + 1/2 O 2(g)? H f Hf H rxn Hrxn 2

3 15. The limiting reagent in a particular reaction can be recognized because it is the reagent that. has the smallest coefficient in the balanced equation has the smallest mass in the reaction mixture is present in the smallest molar quantity would be used up first 16. The correct name for HIO 3(aq) is. hydrogen iodate iodic acid hydroiodic acid hydrogen iodous acid 17. When a material in the liquid state is vaporized and then condensed to a liquid, the steps in the process are, respectively,. exothermic and exothermic exothermic and endothermic endothermic and exothermic endothermic and endothermic 18. In the reaction Pb (s) + PbO 2(s) + 2H 2 SO 4(aq) 2PbSO 4(s) + 2H 2 O (l), which substance behaves as the oxidizing agent? Pb (s) PbSO 4(s) PbO 2(s) H 2 SO 4(aq) 3

4 19. Ammonia, NH 3, reacts with the hypochlorite ion, OCl, to produce hydrazine, N 2 H 4 according to the reaction 2NH 3 + OCl N 2 H 4 + Cl + H 2 O. How many moles of hydrazine are produced from 5.85 moles of ammonia if the reaction has a 78.2% yield? 2.29 moles 2.92 moles 4.57 moles 9.15 moles 20. A mixture containing 9 moles of F 2 and 4 moles of S is allowed to react according to the equation 3F 2 + S SF 6. How many moles of F 2 REMAIN after 3 moles of S have reacted? In the Born-Haber cycle, H atom generally refers to. sublimation ionization electron affinity bond energy 22. If h = 810 mm in a closed-end manometer, then the pressure equals atm 1.07 atm 1.1 atm 2.1 atm 4

5 23. If R = L atm/k mole, then 1 mole of gas occupies (to 3 sig figs) under standard conditions L 22.4 L 24.5 L None of these 24. When 4.50 g of Fe 2 O 3 (MW = g/mole) is reduced with excess H 2 in a furnace according to the reaction Fe 2 O 3(s) + 3H 2(g) 2Fe (s) + 3H 2 O (g), 2.60 g of metallic iron is recovered. What is the percent yield? 82.6% 70.0% 57.8% 31.5% 25. In which compound does vanadium have the lowest oxidation state? V 2 O 5 V 2 O 3 VO 2 VO 26. Which of the following statements is NOT consistent with the kinetic-molecular theory of gases? Gas particles have no volume. Gas particles inelastically collide with each other and the container walls. Gas particles travel in straight lines in between collisions. The average KE of a gas particle is proportional to kelvin temperature. 5

6 27. If 1.0 mole N 2 has T = 200 K, to what temperature must a 2.0 mole sample of N 2 be heated in order to have the same KE as the 1.0 mole sample? 100 K 200 K K 400 K 28. A bomb calorimeter measures. the change in enthalpy for a reaction the change in internal energy for a reaction the heat of reaction at constant temperature the work of a reaction 29. Which of the following is a correct statement of the 1st Law of Thermodynamics? E universe = 0 E system + E surroundings = 0 E system = E surroundings All of these 30. What is the molarity of a solution made by dissolving 8.56 g of sodium acetate (MW = g/mole) in water and diluting to ml? 5.30 M M M M 6

7 Section 3: Long Answer (10 points each) 31. A 2.00 gram glass bead (C s = J/g C) is heated to 25 0 C and then placed in a beaker containing grams of ethanol (C s = 2.46 J/g C) at 21.8 C. Assuming no heat loss, what will be the final temperature once thermal equilibrium is reached? 7

8 32. The reaction below is performed using 115 g of calcium phosphate (MW = g/mole), 71 g of silicon dioxide (MW = g/mole), and 24 g of atomic carbon (MW = g/mole). 7 points. What is the ABSOLUTE MAXIMUM number of grams of molecular phosphorus (MW = g/mole) that can form? 3 points. Pick ONE of the excess reactants and calculate how many grams of that reactant remains after the reaction. 2Ca 3 (PO 4 ) 2(s) + 6SiO 2(s) + 10C (s) 6CaSiO 3(s) + P 4(s) + 10CO (g) 8

9 33. Calculate the density of a g sample of silane, SiH 4(g), at C and 3.00 atm. Note that R = L atm/k mole. 9

10 34. Calculate H rxn for the reaction below given the following bond enthalpies: O-H, 460 kj/mole; O-O, 142 kj/mole; O=O, kj/mole. 2 H O O H O 2 + H H O O 10

11 35. Complete the table below by writing in the missing information. Note that you DO NOT need to balance the equations. Be sure to include states! Reactants Products Reaction Type (i) H 2 SO 4(aq) + NaOH (aq) (ii) PbS (s) + O 2(g) PbO (s) + SO 2(g) (iii) HCl (aq) + NaHCO 3(aq) (iv) K 2 S (aq) + Cd(NO 3 ) 2(aq) 11

12 Answer Key for Exam A Section 1: Matching (10 points) (5) actual yield (4) spectator ions (6) reducing agent (8) chemical change (7) mole ratios (9) 1st Law of Thermodynamics (1) titration (3) complete ionic equation (10) Avogadro s Law (2) calorimetry BE. procedure to find unknown concentration using a known concentration CD. based on q system = q surroundings AE. lists all of the ions present on reactant and product sides BC. do not participate in a reaction AD. limited by side reactions and lab skills BD. the substance that undergoes oxidation AC. conversion factors obtained from balanced equations AB. when atoms rearrange into a new substance CE. E universe = E system + E surroundings DE. more n gas requires more V 1

13 Section 2: Multiple Choice (40 points)

14 Section 3: Long Answer (10 points each) 31. Answer: T f = 23.3 C. 32. Answer: 23.0 g of P 4. 4 g SiO 2 OR 2 g of C. 33. Answer: Density = 3.95 g/l. 34. Answer: H rxn = 215 kj. 35. Answer: (i) Products: Na 2 SO 4(aq) + H 2 O (l), Reaction type: acid/base or neutralization. (ii) Reaction type: redox. (iii) Products: NaCl (aq) + H 2 O (l) + CO 2(g), Reaction type: gas evolution. (iv) Products: KNO 3(aq) + CdS (s), Reaction type: precipitation, metathesis, or double displacement. 3