U N I T T E S T P R A C T I C E

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1 South Pasadena AP Chemistry Name 3 Chemical Equilibrium Period Date U N I T T E S T P R A C T I C E Part 1 Multiple Choice You should allocate 30 minutes to finish this portion of the test. No calculator should be used. A periodic table and data table will be provided. Select the answer that best responds to each question. 1. Hemoglobin (Hb) is a protein with a binding site for oxygen. In cell tissue, the decreased dissolved O 2 causes bound hemoglobin (Hb O 2) to release the oxygen: Hb O 2 Hb + O 2 At a given moment, which of the following provides evidence that equilibrium in a body tissue has been established? (A) The amount of bound hemoglobin and unbound hemoglobin are equal. (B) The amount of bound hemoglobin and unbound hemoglobin do not change. (C) There is no more bound hemoglobin left. (D) There is no more oxygen dissolved in the tissue. 2. Consider the following reversible processes: CaCO 3 (s) Ca 2+ (aq) + CO 3 2 (aq) K c = Ca(OH) 2 (s) Ca 2+ (aq) + 2 OH (aq) K c = HCO 3 (aq) H + (aq) + CO 3 2 (aq) K c = H 2O (l) H + (aq) + OH (aq) K c = What is the value of the equilibrium constant, K c, for the following reaction? CaCO 3 (s) + OH (aq) + H 2O (l) Ca(OH) 2 (s) + HCO 3 (aq) (A) (B) (C) (D) Consider the vaporization of water: H 2O (l) H 2O (g) K p = 1 at 373 K A sample of H 2O (l) is placed in a container where the partial pressure of H 2O (g) is 0.8 atm. Which of the following best describes this process? (A) The rate of condensation is greater than the rate of vaporization. (B) The rate of vaporization is greater than the rate of condensation. (C) Water is vaporizing and condensing at the same rates. (D) The rates of vaporization and condensation cannot be compared. 4. Consider the following process: CO (g) + NO 2 (g) CO 2 (g) + NO (g) The value of K c = 1.5. If 0.5 mol of CO (g), NO 2 (g), CO 2 (g), and NO (g) are placed in a 1.0 L container, in which direction will the reaction shift? (A) There will not be a shift because Q = 1. (B) To the left because Q > K p. (C) To the right because K c > 1. (D) To the right because Q < K p.

2 5. A sample of A (g) was placed in a reaction vessel and allowed to reach equilibrium according to the following reaction: 3 A (g) 4 B (g). The concentration of the substances was plotted against time, and the following graph was produced. concentration (M) time (s) Approximately what is the value of the equilibrium constant, K c? (A) (B) 0.40 (C) 4.0 (D) Consider the following reversible reaction: 2 PF 3 (g) 2 P (s) + 3 F 2 (g) An empty vessel was filled with PF 3 (g) to a pressure of 2.0 atm, and allowed to react until equilibrium was reached. If pressure of the reaction mixture at equilibrium was 2.4 atm, what is the value of K p? (A) 1.2 (B) 0.96 (C) 0.40 (D) For the reaction A (g) + B (g) AB (g) + heat, the following represents the ratio of molecules at equilibrium: A = B = AB = [B] [A] 8. A sample of X (g) is placed in a vessel and brought to equilibrium according to the reaction: X (g) Y (g). When the temperature is decreased, the concentration of Y in the reaction vessel increases. Which of the following could explain this observation? (A) The molecules are colliding with less energy, so the reaction shifts to the right. (B) The reaction is endothermic, so when the temperature is decreased, the reaction shifts to the right. (C) When the temperature is decreased, the value of K increases, so the reaction shifts to the right. (D) When the temperature is decreased, the value of Q also decreases, so the reaction shifts to the right. 9. Consider the process: heat + N 2O 4 (g) + 2 H 2 (g) N 2H 4 (l) + 2 O 2 (g) Which of the following will increase the yield of N 2H 4 (l)? (A) Adding O 2 (g) to the reaction mixture. (B) Decreasing the temperature. (C) Decreasing the volume of the container. (D) Removing H 2 (g) from the reaction mixture. 10. Consider the following process: 2 HI (g) H 2 (g) + I 2 (s) To a reaction at equilibrium, some I 2 (s) is added. How will the amount of HI (g) change? (A) It cannot be predicted how the amount of HI will change because the value of K eq is not given. (B) The amount of HI (g) will decrease since Q < K eq. (C) The amount of HI (g) will increase since Q > K eq. (D) The amount of HI (g) will remain unchanged as Q = K eq. What can be concluded about the value of K p? (A) K p >> 1 (B) K p 1 (C) K p << 1 (D) Nothing can be concluded about the magnitude of K p.

3 11. A saturated solution was prepared by placing solid Ag 2CrO 4 in pure water. If [Ag + ] = M. what is the value of the solubility product of Ag 2CrO 4? (A) (B) (C) (D) Use the following data: K sp for AgCl is K sp for Ag 2CO 3 is Flask A contains a saturated solution of AgCl, and flask B contains a saturated solution of Ag 2CO 3. These solutions were prepared by placing the solids in 50.0 ml pure water. Which flask contains a higher concentration of Ag +? (A) Flask A because AgCl has a larger K sp. (B) Flask B because Ag 2CO 3 has a higher K sp. (C) Flask A because AgCl has higher molar solubility. (D) Flask B because Ag 2CO 3 has higher molar solubility. 13. The K sp of lead iodide is To a 1.0 L solution containing M Pb(NO 3) 2, solid KI is slowly added. What is the maximum amount of KI that could be added before a precipitate starts to form? (A) mol (B) mol (C) mol (D) mol 14. Addition of all of the following will affect the solubility of FeCO 3 except: (A) H 2CO 3 (B) HCl (C) Na 2CO 3 (D) NaCl mol NaCl and mol AgCl are combined in a 1.0 L solution. What is the value of [Ag + ] in this solution? The K sp of AgCl is (A) M (B) M (C) M (D) M

4 Part 2 Free Response You should allocate 30 minutes to finish this portion of the test. You may use a scientific calculator. A periodic table and data table will be provided. Respond to each part of the questions completely. Be sure to show your work clearly for questions that involve calculators. 16. Answer the following questions about the solubility of silver carbonate, Ag 2CO 3. At 25 C, the solubility product, K sp, of Ag 2CO 3 is (a) Write the dissociation equation for silver carbonate. (b) A g sample of Ag 2CO 3 (molar mass g mol 1 ) is placed in pure water to form a 1.00 L solution, and a precipitate forms. i. Find the concentration of Ag + in mol L 1. ii. What is the minimum volume of water that should be added to dissolve all of the precipitate? (c) What is the molar solubility of Ag 2CO 3 in a M AgNO 3 solution? (d) Consider the following process: Ag + (aq) + 2 NH 3 (aq) Ag(NH 3) 2 + (aq) K c = i. Find the value of K c for the reaction: Ag 2CO 3 (s) + 4 NH 3 (aq) 2 Ag(NH 3) CO 3 2 ii. Does the addition of NH 3 increase, decrease, or has no effect on the solubility of Ag 2CO 3? Justify your answer.

5 17. Consider the following reaction: SO 3 (g) + SCl 2 (g) SOCl 2 + SO 2 (g) + heat At a particular temperature K p = A reaction mixture contains the following in a 2.0 L container: P SO3 = 0.25 atm PS Cl2 = 0.50 atm P SOCl2 = 1.00 atm P SO2 = 1.00 atm (a) Write the equilibrium constant expression, K p, for the reaction. (b) Determine whether the reaction mixture is at equilibrium, or which direction it will shift. Justify your answer. (c) What is the value for K c? Explain. (d) If the temperature is raised, will the value for K p increase or decrease or remain the same? Justify your answer.

6 South Pasadena AP Chemistry Name 3 Chemical Equilibrium Period Date U N I T T E S T B L U E P R I N T Part 1: Multiple Choice Format: 15 questions, four answer choices: (A)-(D) Expected time: 30 minutes Allowed resources: Periodic Table, Equations and Constants. No calculators. Q Lesson Topic Objective Equilibrium Mixture Describe the reaction mixture of a system at equilibrium qualitatively, graphically, and quantitatively Equilibrium Constant Write and find the value for the equilibrium expression when the balanced equation is changed or when equations are combined Reaction Quotient Le Chatelier s Equilibrium Constant Write the mass action expression of a reversible reaction in concentrations (Q c or K c) and pressures (Q p or K p) Solving Equilibrium Problems Determine the concentrations of substances at equilibrium using an ICE Chart Equilibrium Mixture Describe the reaction mixture of a system at equilibrium qualitatively, graphically, and quantitatively Le Chatelier s Le Chatelier s Le Chatelier s Solubility Equilibrium Compare solubilities of various insoluble salts and use them to selectively precipitate various ions. Calculate the solubility of an insoluble salt using an ICE Box Solubility Product Write the expressions for the solubility product (K sp) Precipitation Determine whether precipitation occurs when solutions are combined Common Ions Predict how ions in solution affect the solubility of a salt Common Ions Calculate the solubility of a salt in a solution with a common ion. Part 2: Free Response Format: o 1 long question (5-8 parts) o 1 short questions (2-4 parts) Expected time: 30 minutes Allowed resources: Periodic Table, Equations and Constants, and scientific calculators. Topics: Any