1. Consider the following Lewis structure: Which statement about the molecule is false?

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1 CHY 116 Final Exam, Spring 2017 Multiple Choice (68 points): Each question is intended to have one correct answer. Please write this answer on the answer sheet. Each question is worth 1.25 points. 1. Consider the following Lewis structure: Which statement about the molecule is false? a. Some of the H C H bonds have bond angles of about 109. b. C-2 is sp 2 hybridized with bond angles of 120. c. The bond angles at C-3 are 90 0 and d. There are 10 sigma and 2 pi bonds. e. This molecule contains 28 valence electrons 2. Atoms that are sp 2 hybridized can form pi bond(s). a. 0 b. 1 c. 2 d What hybridization is predicted for the carbon atom in carbon dioxide? (Lewis structure for CO2 needed to answer.) a. sp b. sp 2 c. sp 3 d. sp 3 d 4. The hybridization of Br in BrF3 is: a. sp b. sp 2 c. sp 3 d. sp 3 d 5. The strongest intermolecular force formed between water molecules is a. dispersion force b. covalent bond c. hydrogen bond d. ionic bond 6. What volume of 3.0 M H2SO4 is needed to prepare ml of 0.15 M H2SO4? a. 15 ml b. 20. ml c. 42 ml d L grams of calcium chloride is dissolved in enough water to make ml of solution. The molarity of the solution is: a M b M c M d M 8. Calculate the molality of C2H5OH in a water solution that is prepared by mixing 50.0 ml of C2H5OH with ml of H2O at 20 C. The density of the C2H5OH is g/ml at 20 C. (Assume the density of water at this temperature is 1.00 g/ml.) a) m b) m c) m d) 7.90 m e) 10.0 m 9. A 20.0-g sample of methyl alcohol (CH3OH, molar mass = g/mol) is dissolved in 35.6 g of water. The mole fraction of CH3OH in this solution is: a) b) c) d) 4.17 e) 0.240

2 10. Given the graph below, the normal boiling point of chloroform is estimated to be a) 77 C b. 34 C c. 98 C d. 60 C e) The graph does not give that information. 11. The solubility of a gas in a liquid is related to temperature. a) directly b) inversely Use the following to answer questions 12-14: A general reaction written as A + 2B C + 2D is studied and yields the data shown below. [A]0 [B]0 Initial rate production C M M M/s M M M/s M M M/s 12. What is the order of the reaction with respect to A? a. 0 b. 1 c. 2 d What is the order of the reaction with respect to B? a. 0 b. 1 c. 2 d What is the numerical value of the rate constant? a b c d Which of the following is true for a system whose equilibrium constant is very small, ~10-12? a) It will take a short time to reach equilibrium. b) It will take a long time to reach equilibrium. c) The products are highly favored and the reaction essentially goes to completion. d) The reactants are highly favored and essentially no product is formed.

3 16. Which of the following is true about a system at equilibrium? a) The concentration(s) of the reactant(s) is equal to the concentration(s) of the product(s). b) No new product molecules are formed. c) The concentration(s) of reactant(s) is constant over time. d) The value of k is equal to 1.00 when equilibrium is reached. 17. For the equilibrium reaction given below, 2.00 moles of A and 3.00 moles of B are placed in a 6.00-L container. At equilibrium, the concentration of A is mol/l. What is the concentration of B at equilibrium? (ICE Table needed.) A(g) + 2B(g) C(g) a M b M c M d M 18. If the equilibrium constant for A + B C is 0.180, then the equilibrium constant for 2C 2A + 2B is a) b) 5.56 c) d) 30.9 e) Consider the following equilibrium for questions A(g) 2B(g) + C(g). Delta H = -27 kj 19. Addition of chemical B to an equilibrium mixture of the above will a) cause [A] to increase b) cause [C] to increase c) have no effect d) cannot be determined 20. Placing the equilibrium mixture in an ice bath will a) cause [A] to increase b) cause [B] to increase c) have no effect on the position of the equilibrium 21. Raising the pressure by lowering the volume of the container will a) cause [A] to increase b) cause [B] to increase c) have no effect on the position of the equilibrium 22. Hydrogen ions formed in water form bonds with water molecules. a. Ionic b. Hydrogen c. Coordinate covalent d. Acid 23. Write the Ka expression associated with an aqueous solution of the weak acid HNO2 on the answer sheet. Ka = 24. Which of the following is a conjugate acid/base pair? a. HCl and OCl - c. H2SO4 and SO4-2 b. H3O + and OH - d. NH4 + and NH3

4 25. The hydrogen sulfate ion HSO4-1 can act as either an acid or a base in water. In which of the following equations correctly shows HSO4 - behaving as an acid? a. HSO4-1 + H2O H2SO4 + OH -1 b. HSO4-1 + H3O + SO3 + 2 H3O + c. HSO4-1 + H2O SO4-2 + H3O + d. HSO4-1 + OH - H2SO4 + O The Ka value for a strong acid is a. Very small and difficult to measure b. Very large and difficult to measure c. Very small and easy to measure d. Very large and easy to measure 27. Which of the following could not be amphoteric? a. H2PO4-1 b. HSO4-1 c. H2O d. SO4-2 Consider the following Ka values for questions a. NH4 + Ka = 5.6 x b. HOCL Ka = 3.5 x 10-8 c. HC2H3O2 Ka = 1.8 x 10-5 d. HF Ka = 7.2 x Which of the acids shown above is the strongest acid? (use letters above) 29. Which of the acids shown above has the strongest conjugate base? 30. If a 1.0 M solution was made of each of the acids shown above, which solution would have the highest ph? 31. Which of the acids shown above has a Kb of 2.9 x 10-7? 32. Which of the following is not true concerning a solution at 25 0 C that has a hydroxide concentration of 2.5 x 10-6 M? a. It is a base. b. It s ph is 5.60 c. The [H3O + ] is 4.0 x 10-9 M d. The Kw for this solution is 1.0 x The ph of a M HNO3 solution is: a b c d The ph of acid rain may be as low as What is the concentration of hydrogen ions in such acid rain? a M b M c. 1.6 x 10-3 M d. 6.3 x M

5 35. The source of hydrogen ions in an aqueous mixture of weak acids is primarily from the a. ionization of water. b. ionization of the weakest acid present c. ionization of the strongest acid present d. conjugate base of the acid 36. The ph of a 0.02 M KOH solution is a. 1.7 b. 2.0 c d The poh of a 0.10 M solution of Ba(OH)2 is a b c d The Ka for the ionization of the first hydrogen ion of a polyprotic acid is 1.3 x The Ka for ionization of the second hydrogen ion a. Is also 1.3 x 10-4 b. Is greater than 1.3 x 10-4 c. Is smaller than 1.3 x 10-4 d. Cannot be predicted 39. An acid with a relatively small percent dissociation value will a. have a relatively high Ka value b. have a relatively low Ka value c. be a strong acid d. have a very weak conjugate base 40. Consider the K values below when answering this question. Which of the following solutions will have the highest ph? a. 2.0 M HClO4 Ka = 3.5 x 10-8 b. 2.0 M NH3 Kb = 1.8 x 10-5 c. 2.0 M pyridine Kb = 1.7 x 10-9 d. 2.0 M aniline Ka = 2.6 x Identify an aqueous solution of each of the following as a. Acidic b. basic c. Neutral 41. Solution of NaNO3 42. Solution of NaCN 43. Solution of C6H5NH3Cl 44. Which of the following factors is most important in determining the acid strength of an oxyacid? e. The size of the molecule. f. The identity of the central atom in the molecule. g. The number of oxygens in the molecule

6 45. Calculate the ph of a solution that is 0.50 M in HF (Ka = 7.2 x 10-4 ) and 0.60 M in NaF b c d What is the ph of a solution that is 1.5 M NH3 (Kb = 1.8 x 10-5 ) and 1.5 M NH4Cl. a b c d Which of the following would be the best choice for making a buffer of ph 4? a. Lactic acid Ka = 1.4 x 10-4 b. HCN Ka = 6.2 x c. Phenol Ka = 1.6 x d. HF Ka = 3.5 x Which of the following would be the best buffer at ph 9.26? a M HC2H3O2 (Ka = 1.8 x 10-5 ) and 0.10 M Na C2H3O2 b. 5.0 M HC2H3O2 (Ka = 1.8 x 10-5 ) and 5.0 M Na C2H3O2 c M NH3 (Kb = 1.8 x 10-5 ) and 0.10 M NH4Cl d. 5.0 M NH3 (Kb = 1.8 x 10-5 ) and 5.0 M NH4Cl 49. The addition of NaCN to a solution of the weak acid HCN will a. Lower the ph of the solution b. Raise the ph of the solution c. Not change the ph of the solution. 50. Consider two buffer solutions: Buffer A: 3.0 M HOCl and 3.0 M NaOCl; Buffer B: 0.50 M HOCl and 0.50 M NaOCl. How do the phs of these solution compare? a. The ph of Buffer A is higher than that of Buffer B. b. The ph of Buffer A is lower than that of Buffer B. c. Both buffers will have the same ph. d. No conclusions can be drawn about their phs without a Ka value. Consider the carbonic acid/carbonate buffer system for questions 51-52: H2CO3 + H2O HCO3-1 + H3O Any HCl added to this buffer will react with the a. H2CO3 b. H2O c. HCO3-1 d. H3O Any NaOH added to this buffer will react with the a. H2CO3 b. H2O c. HCO3-1 d. H3O Which of the following sulfides is most soluble in water? a. MnS Ksp = 2.3 x c. CuS Ksp = 8.5 x b. CoS Ksp = 5 x d. HgS Ksp = 1.6 x What is the molarity of a saturated solution of AgOH (Ksp = 2.0 x 10-8 )? a. 1.4 x 10-4 M b. 2.0 x 10-8 M c. 4.0 x M d. 1.0 x 10-8 M

7 PART II: Problem Solving Answer 2 of the following problems (3 options). Show all work for full credit. 8 pts each A. In a recent study by Cornell University, Grade A dark maple syrup was found to be 66.2 % sucrose (C12H22O11) by mass. Assume this is the sucrose content of maple sugar for all questions that follow. a. Calculate the mole fraction of sucrose in maple syrup and the molality of maple syrup. Assume water is the solvent. b. Based on your answer to a, calculate the boiling point and the freezing point of maple syrup. c. In reality maple syrup contains many solutes in addition to sucrose. Given this, if you were to take the boiling point of maple syrup would that boiling point be higher than, less than or equal to the boiling point you calculated in b? Explain your answer.

8 B. The breakdown of the antihistamine diphenhydramine is a first order reaction. In children this breakdown has a half-life of 5.3 hours, while in the elderly the half-life for the breakdown of this medication is 11.7 hours. Select children or the elderly for question a and b. a. Determine the value of k for this medication in either the elderly or for children. Clearly indicate if you have selected children or the elderly. (2 points) b. (I am making the next part up.) To avoid a potential overdose, a second dose should not be given until the level of the medication from the first dose has dropped by 80.0%. Continue answering this question for children or the elderly. How many hours would does it take for the concentration of diphenhydramine to drop by 80.0% in the population you have selected? (4 points) c. Assume the same dose, in mg/kg body weight, of this medication is given to a child and to an older person. A second dose is then taken earlier than the prescribed amount of time. Who is more likely to experience overdose symptoms, the child or the older person? Explain your answer. (2 points)

9 C M CO, M H2O are combined in a closed container and allowed to establish an equilibrium. What is the concentration of each member of the reaction at equilibrium? Show work for full credit. (8 points) CO(g) + H2O(g) H2(g) + CO2(g) Kc = 4.03

10 2. Answer any three of the following: 5 options pick any 3! (4 points each = 12 points) A. Determine the ph and percent dissociation of a 3.5 M HOCl solution. Show that any assumption made is appropriate. B. Consider a solution that is 1.50 M HF (Ka = 7.2 x 10-4 ) and 2.00 M HCN (Ka = 6.2 x ). What is the ph of this solution and the CN -1 concentration of this solution?

11 C. Calculate the ph of a 2.5 M ascorbic acid solution. Ka1 = 8.0 x 10-5 Ka2 = 1.6 x D. Calculate the ph of a solution that is 0.75 M ethylamine and 1.5 M C2H5NH3Cl E. A key buffer system in the body is the carbonic acid/carbonate buffer, shown below. Calculate the ratio of carbonate ion to carbonic acid in a solution of this buffer that has a ph of 7.3. The first Ka for carbonic acid is 4.3 x H2CO3 + H2O H3O + + HCO3 -

12 3. A simplified version of the why Flint Michigan s water system became contaminated by high levels of lead ions. The lead contamination problem in Flint s water system occurred when a change in water source/processing resulted in the breakdown of a protective layer of lead phosphate that had previously lined the lead water pipes. This layer of lead phosphate was maintained by adding phosphates to the water. When a switch was made to using water from the Flint River, the process of adding phosphates to the water stopped and the protective layer slowly broke down exposing bare lead pipes. As a result the lead pipes reacted with chloride ions in the chlorinated water to form lead chloride. Research the Ksp values for lead (II) phosphate and lead (II) chloride. Use these values to explain why lead (II) phosphate offers a protective layer and how adding phosphate to the water helps maintain that protective layer. In addition, explain lead levels in the water went up when the protective layer was gone.