Final exam practice problems

Final Exam Practice Problems
(Answers at end)
Honors Chemistry
Formulas
1. A compound containing carbon and hydrogen in a mole ratio of 1 to 2 has a molecular weight of 42. What is its molecular formula? 2. What is the percentage by mass of carbon in oxalic acid, H2C2O4? 3. Dysprosium oxide, Dy2O3, reacts with hydrochloric acid to produce only water and a salt. 4. A sample of Ni3(PO4)2•8H20 contains 0.25 mol of phosphorus. How many moles of water 5. When 10.0 g of molybdenum metal, Mo, react with an excess of sulfur, S, the metal sulfide has a mass of 16.6 g. What is the formula of the metal sulfide? Reactions and Stoichiometry
6. Using only whole numbers, what is the coefficient of oxygen when this equation is ___ FeS2 + ___ O2  ___ Fe2O3 + ___ SO2 7. When 10.0 g of ethene reacts with excess bromine, 20.0 g of dibromomethane forms. What CH4 (g) + 2 O2 (g)  CO2 (g) + 2 H2O (g) If 32 g of methane, CH4, and 32 g of oxygen, O2, react, the quantity of reactant remaining is 9. What is the sum of the coefficients of the following equation when it is balanced? If 5.8 grams of Ag(NH3)+1 yields 1.4 g of ammonia, how many moles of silver ion are produced? 11. Aspirin (C9H8O4) is prepared by the following reaction: How many moles of salicylic acid (C7H6O3) are needed to prepare six 5 grain aspirin tablets? (1 gram = 15.5 grains) III. Gases
12. A 322 mL sample of warm HCl solution is reacted with excess Zn. The volume of dry H2 collected at 31C and 0.92 atm is 5.21 L. What is the original molarity of the hydrochloric acid? Zn (s) + 2 H+1(aq)  Zn +2 (aq) + H2 (g) 13. What is the pressure of 0.100 g of NO2 at 25C in a sealed 500 mL container? 14. A flask holds 3.00 moles of hydrogen, H2. It is emptied and then filled with methane, CH4, at the same temperature and pressure. What mass of methane does it hold? 15. 0.500 mol of hydrogen, H2, 0.500 mole of nitrogen, N2, and 1.00 mole of helium, He, are placed in the same container, giving an internal pressure of 860 mm Hg. What is the partial pressure, in torr, due to hydrogen, H2? CH4 (g) + 2 O2 (g)  CO2 (g) + 2H2O (l) What volume of carbon dioxide, CO2, at STP is produced by burning 16.00 g of ethane in excess oxygen? 17. What is the molar mass of a gas that diffuses at one-third the rate of methane, CH4? 18. To what Celsius temperature must 40.0 L of gas at 22C be changes so it has a volume of 19. What volume will 19.6 g of methane, CH4, occupy at 27C and 1210 mm Hg? 20. What is the density of a gas at 76 torr and 37C (MM = 25 g)? 21. A sample containing CO2, O2, and N2 is enclosed in a container at 25C and standard pressure. The average kinetic energy of the O2 molecules is: a. less than the average kinetic energy of N2 molecules b. greater than the average kinetic energy of CO2 molecules c. equal to the kinetic energy of each individual O2 molecule d. equal to the average kinetic energy of both N2 and CO2 molecules IV. Solutions
22. Which 0.100 m aqueous solution will have the lowest vapor pressure at 25C? 23. A 6.25 M aqueous solution of sodium hydroxide, NaOH, has a density of 1.22 g/mL. 24. Data are collected to determine the molar mass of an unknown organic substance. The experimentally determine molar mass (in grams) is ____. unknown organic compound in camphor Kf of camphor 25. To what volume must 10.0 mL of 5.0 M HCl be diluted to make a 0.50 M solution? 26. Which of the following will be the most electrically conductive? 27. Which of the following correctly describes the solubility of potassium chloride (KCl)? V. Equilibrium
28. Equal volumes of 0.100 M Pb(NO3)2 and 0.100 M KI are mixed. The ion in the resulting solution with the lowest concentration is ____. (Ksp for PbI2 = 8.4 x10-9) Which combination of conditions favors the production of ammonia, NH3? Temperature
Pressure
30. Initially, all four gases in this reaction are at the same concentration of 5.0 x 10-3M. When equilibrium is established, what is the concentration of SO3? Keq = 33 at 773 K. 31. Determine the solubility of La(OH)3 (Ksp = 2.0 x 10-21) in a 0.030 M aqueous NaOH solution. 32. Exactly 2.50 mol nitrosyl chloride, NOCl, is placed in a closed 1.50 L container and heated to 400C. At equilibrium 28.0% of the NOCl is dissociated. What is the value of the equilibrium constant for this reaction? At equilibrium the concentrations are [CO] = 2.0, [O2] = 1.0, and [CO2] = 16. What is the value of the equilibrium constant, Keq? 34. If K >>1, the equilibrium mixture c. amount of products and reactants are equal VI. Acids and Bases
35. Which aqueous solution is most acidic? 36. What is the concentration of hydroxide ion, [OH-1], in a 0.0020 M HCl solution? 37. Consider the acids given in the following table. Which has the strongest conjugate base? 38. What is the pH of a saturated solution of Ca(OH)2? Ksp of Ca(OH)2 = 1.36 x 10-6 39. What is the pH after 20.0 mL of 0.10 M NaOH solution is mixed with 10.0 mL of 0.10 M HCl 40. What volume of 0.150 M NaOH is needed to neutralize 30.0 mL 0f 0.500 M HNO3? NH3 (aq) + H2O (l)  NH4+1 (aq) + OH-1 (aq) VII. Thermochemistry
42. Which changes are accompanied by an increase in entropy? 43. A certain reaction is spontaneous at room temperature. At lower temperature the reaction is non-spontaneous. Which could be true for this reaction? 16.2 kcal + N2 (g) + 2 O2 (g)  2 NO2 (g) Calculate the heat of formation (Hf) for one mole of NO2 (g). 45. Given the data provided in the table below, determine the heat of reaction, Hrxn for: CH3CH2OH (l) + 3O2 (g)  2 CO2 (g) + 3 H2O(l) Reaction
H (kJ/mol)
CH3CH2OH (g) + 3 O2(g)  2 CO2 (g) + 3 H2O (g) 46. As solid NH4NO3 dissolves in water, the solution becomes colder. Which are the correct 47. How much heat must be removed from 20.0 g of a liquid at 55.0C to completely freeze it at 48. What is the heat capacity of a 10.0 g sample that has absorbed 100 cal over a temperature 49. A 50.0 g sample of metal was heated to 100C and the dropped into a beaker containing 50 g of water at 25C. If the specific heat of the metal is 0.25 cal/gC, what is the final temperature of the water? VIII. Kinetics
50. Kinetic data are obtained for the reaction: H3AsO4 + 2H3O+1 +3I-1 HAsO2 + I3-1 +4H2O [H3AsO4]
Initial Rate
51. All of the following are true statements concerning reaction orders except: a. the rate of a zero order reaction is constant b. After three half-lives, a radioactive sample will have one-ninth of its original c. The units for the rate constant for a first order reaction is sec-1 d. If doubling the concentration of a reactant doubles the rate of the reaction, then the reaction is first order in that reactant. 52. Which is most likely to increase the rate of a reaction? a. decreasing the temperature b. increasing the volume of the reaction vessel c. reducing the activation energy d. decreasing the concentration of the reactant(s) 53. The number of undecayed nuclei in a sample of bromine-87 decreased by a factor of 4 over a period of 112 seconds. What is the rate constant for the decay of bromine-87? 54. The equilibrium constant, Keq, of a certain first order reaction is 0.16. A catalyst is added to the reaction. The the equilibrium constant for the catalyzed reaction is: 55. The activation energy for a reaction in the forward direction is 78 kJ. The activation energy for the same reaction in the reverse direction is 300kJ. If the energy of the products is 25 kJ, what is the enthalpy change for the forward reaction?
Answers to Honors Practice Final Exam

1. ignore 21. D

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