What do I need to know in order to solve this questions. Go in the order of the questions?
2023 AP® Chemistry Free-Response Questions © 2023 College Board. College Board, Advanced Placement, AP, AP Central, and the acorn logo are registered trademarks of College Board. Visit College Board on the web: collegeboard.org. AP Central is the official online home for the AP Program: apcentral.collegeboard.org. 2 AP® CHEMISTRY EQUATIONS AND CONSTANTS Throughout the exam the following symbols have the definitions specified unless otherwise noted. L, mL = liter(s), milliliter(s) g = gram(s) nm = nanometer(s) atm = atmosphere(s) mm Hg = millimeters of mercury J, kJ = joule(s), kilojoule(s) V = volt(s) mol = mole(s) ATOMIC STRUCTURE E = energy  = frequency  = wavelength Planck’s constant, h = 6.626  1034 J s Speed of light, 1 c = 2.998  108 m s Avogadro’s number = 6.022  1023 mol1 Electron charge, e = 1.602 × 1019 coulomb E = h c =  EQUILIBRIUM Equilibrium Constants Kc (molar concentrations) Kp (gas pressures) Ka (weak acid) Kb (weak base) Kw (water) c d [C] [D] Kc = , where a A + b B  c C + d D a b [A] [B] c d ( ) ( P P ) C D Kp = a b ( ) ( P P ) A B + - [H ][A ] Ka = [HA] - + [OH ][HB ] Kb = [B] K = [H+][OH] = 1.0  1014 w at 25C = Ka  Kb pH = log[H+] , pOH = log[OH] 14 = pH + pOH [A - ] pH = pK + log a [HA] pKa = logKa , pKb = logKb KINETICS k = rate constant t = time t ½ = half-life [A]t  [A] 0 =  kt ln[A]t  ln[A] 0 =  kt 1 1 - = kt [] [] A A t 0 0.693 t ½ = k 3 GASES, LIQUIDS, AND SOLUTIONS P = pressure V = volume T = temperature n = number of moles m = mass M = molar mass D = density KE = kinetic energy v = velocity A = absorbance  = molar absorptivity b = path length c = concentration Gas constant, R = 8.314 J mol1K1 = 0.08206 L atm mol1 K1 = 62.36 L torr mol1 K1 1 atm = 760 mm Hg = 760 torr STP = 273.15 K and 1.0 atm Ideal gas at STP = 22.4 L mol−1 PV = nRT moles A PA = Ptotal  XA, where XA = total moles = PA + PB + PC P + . . . total m n = M K = C + 273 m D = V 1 KEmolecule = mv 2 2 Molarity, M = moles of solute per liter of solution A =  bc THERMODYNAMICS / ELECTROCHEMISTRY q = heat m = mass c = specific heat capacity T = temperature S = standard entropy H = standard enthalpy G = standard Gibbs free energy n = number of moles E = standard reduction potential I = current (amperes) q = charge (coulombs) t = time (seconds) Q = reaction quotient Faraday’s constant, F = 96,485 coulombs per mole of electrons 1 joule 1 volt = 1 coulomb q = mcT S =  S products -  S reactants H    =  DH products -  DH reactants f f G    =  DGf products -  DGf reactants G = H  TS = RT ln K =  nF E q I = t o RT Ecell = Ecell - lnQ nF 4 AP® Chemistry 2023 Free-Response Questions Begin your response to QUESTION 1 on this page. CHEMISTRY SECTION II Time—1 hour and 45 minutes 7 Questions Directions: Questions 1–3 are long free-response questions that require about 23 minutes each to answer and are worth 10 points each. Questions 4–7 are short free-response questions that require about 9 minutes each to answer and are worth 4 points each. For each question, show your work for each part in the space provided after that part. Examples and equations may be included in your responses where appropriate. For calculations, clearly show the method used and the steps involved in arriving at your answers. You must show your work to receive credit for your answer. Pay attention to significant figures. 1. Answer the following questions related to manganese compounds. (a) Manganese has several common oxidation states. (i) Write the complete electron configuration for an Mn atom in the ground state. (ii) When manganese forms cations, electrons are lost from which subshell first? Identify both the number and letter associated with the subshell. A student performs an experiment to produce a manganese salt of unknown composition, MnxCly(aq), and determine its empirical formula. The student places a sample of Mn(s) in a beaker containing excess HCl(aq), as represented by the following equation. GO ON TO THE NEXT PAGE. © 2023 College Board. Visit College Board on the web: collegeboard.org. 5 y x Mn(s) + y HCl(aq) → MnxCly(aq) + H ( 2 g) 2 AP® Chemistry 2023 Free-Response Questions Continue your response to QUESTION 1 on this page. The student heats the resulting mixture until only MnxCly(s) remains in the beaker. The data are given in the following table. Mass of empty beaker 60.169 g Mass of beaker and Mn(s) 61.262 g Mass of beaker and Mn Cl after heating to constant mass x y 62.673 g (b) Calculate the mass of Cl in the sample of MnxCly(s) remaining in the beaker. (c) Calculate the number of moles of Cl in the sample of MnxCly(s) remaining in the beaker. (d) The student determines that 0.0199 mol of Mn was used in the experiment. Use the data to determine the empirical formula of the Mn Cl (s) x y . (e) The student repeats the experiment using the same amounts of Mn and HCl and notices that some of the MnxCly splatters out of the beaker as it is heated to dryness. Will the number of moles of Cl calculated for this trial be greater than, less than, or equal to the number calculated in part (c) ? Justify your answer. GO ON TO THE NEXT PAGE. © 2023 College Board. Visit College Board on the web: collegeboard.org. 6 AP® Chemistry 2023 Free-Response Questions Continue your response to QUESTION 1 on this page. (f) Another compound of manganese, MnO2, is used in alkaline batteries, represented by the following diagram. Some half-reactions are given in the table. (i) Based on the half-reactions given in the table, write the balanced net ionic equation for the reaction that has the greatest thermodynamic favorability. (ii) Calculate the value of Ecell for the overall reaction. (iii) Calculate the value of ΔG° in kJ/molrxn. (iv) A student claims that the total mass of an alkaline battery decreases as the battery operates because the anode loses mass. Do you agree with the student’s claim? Justify your answer. GO ON TO THE NEXT PAGE. © 2023 College Board. Visit College Board on the web: collegeboard.org. 7 2. In the gas phase, AlCl3 is a molecular substance. A reaction of gaseous AlCl3 at high temperature is represented by the following balanced equation. Reaction 1: AlCl 3(g) → Al(g) + 3 Cl(g) ΔH = ? 1 AP® Chemistry 2023 Free-Response Questions Begin your response to QUESTION 2 on this page. (a) How many grams of Cl(g) can be formed from 1.25 mol of AlCl3(g) ? Additional reactions that involve Al or Cl are shown in the following table. Reaction Number Equation ΔH (kJ/mol ) rxn rxn 2 3 Al(s) + Cl (g) → AlCl (g) 2 3 2 −583 3 Al(s) → Al(g) +326 4 Cl 2(g) → 2 Cl(g) +243 (b) Calculate the value of ΔH1 , in kJ/molrxn, for reaction 1 above using reactions 2, 3, and 4. GO ON TO THE NEXT PAGE. © 2023 College Board. Visit College Board on the web: collegeboard.org. 8 AP® Chemistry 2023 Free-Response Questions Continue your response to QUESTION 2 on this page. (c) A potential energy diagram for Cl2 is shown in the following graph. (i) Based on the graph, what is the bond length, in picometers, for Cl2 ? _________ (ii) A student finds that the average Al − Cl bond length is 220 picometers and the average bond energy is 425 kJ/mol. Draw the potential energy curve for the average Al − Cl bond on the preceding graph. (d) Three proposed Lewis diagrams for the AlCl3(g) molecule are shown. (i) The AlCl3(g) molecule has a trigonal planar geometry. Which diagram (1, 2, or 3) can be eliminated based on geometry? Justify your choice based on VSEPR theory. GO ON TO THE NEXT PAGE. © 2023 College Board. Visit College Board on the web: collegeboard.org. 9 AP® Chemistry 2023 Free-Response Questions Continue your response to QUESTION 2 on this page. (ii) Which of the three diagrams is the best representation for the bonding in AlCl3 ? Justify your choice based on formal charges. AlCl3 is known to dimerize reversibly in the gas phase. The dimerization equilibrium is represented by the following equation. 2 AlCl3(g) Al2Cl6(g) (e) Write the expression for the equilibrium constant, Kp, for this reaction. A particle-level diagram of an equilibrium mixture of AlCl3(g) and Al2Cl6(g) at 400°C in a 25 L closed container is shown. (f) Using the particle-level diagram, calculate the value of Kp for the reaction if the total pressure in the container is 22.1 atm. GO ON TO THE NEXT PAGE. © 2023 College Board. Visit College Board on the web: collegeboard.org. 10 AP® Chemistry 2023 Free-Response Questions Begin your response to QUESTION 3 on this page. 3. Answer the following questions about an experiment in which CaCO3(s) is combined with HCl(aq), represented by the following balanced equation. CaCO3(s) + 2 HCl(aq) → CaCl2(aq) + CO2(g) + H2O(l) (a) Write the balanced net ionic equation for the reaction. A student performs an investigation to study factors that affect the rate of the reaction. In each trial the student combines 50.0 mL of HCl(aq) at 21.2° C with 1.00 g of CaCO3(s) and measures the time required for the reaction to go to completion. The data are given in the following table. Trial Concentration of HCl(aq) (M ) Particle Size of CaCO (s 3 ) Time of Reaction (s) 1 1.00 Fine powder 67 2 1.00 Small chunks 112 3 1.00 Large chunk 342 4 3.00 Fine powder 22 5 3.00 Small chunks 227 6 3.00 Large chunk 114 (b) The student correctly identifies that trial 5 is inconsistent with the other trials. Explain why the student’s claim is correct using the data in the table. GO ON TO THE NEXT PAGE. © 2023 College Board. Visit College Board on the web: collegeboard.org. 11 AP® Chemistry 2023 Free-Response Questions Continue your response to QUESTION 3 on this page. (c) Based on the reaction conditions and the collisions that occur between particles, explain the reason for the difference in the reaction times for trial 2 and trial 3. (d) The student claims that the reaction is zero order with respect to HCl(aq). Do you agree or disagree with the student’s claim? Justify your answer using the student’s data. (e) The HCl(aq) was present in excess in all trials of the experiment. Determine the molarity of the HCl(aq) in the beaker after the reaction is complete in trial 2. Assume that the volume of the mixture remains constant at 50.0 mL throughout the trial. (The molar mass of CaCO3 is 100.09 g/mol.) GO ON TO THE NEXT PAGE. © 2023 College Board. Visit College Board on the web: collegeboard.org. 12 AP® Chemistry 2023 Free-Response Questions Continue your response to QUESTION 3 on this page. CaCO3(s) + 2 HCl(aq) → CaCl2(aq) + CO2(g) H+ 2O(l) In order to measure the enthalpy of the reaction shown, the student repeats trial 1 by mixing 50.0 mL of HCl(aq) with 1.00 g of CaCO3(s) using a coffee cup calorimeter. The student records the temperature of the system every 20 seconds. The data are given in the following table. Time (s) Measured Temperature of Solution ( C) ° 0 21.20 20 21.51 40 21.70 60 21.85 80 21.90 100 21.90 (f) Is the reaction endothermic or exothermic? Justify your answer using the information in the table. GO ON TO THE NEXT PAGE. © 2023 College Board. Visit College Board on the web: collegeboard.org. 13 AP® Chemistry 2023 Free-Response Questions Continue your response to QUESTION 3 on this page. (g) Based on the experimental data, the mass of the system is 51.0 g, and the specific heat of the reaction mixture is 4.0 J / (g · ° C). (i) Calculate the magnitude of heat transfer, q, in joules. (ii) Calculate the enthalpy of reaction in units of kJ/molrxn. Include the algebraic sign on your answer. GO ON TO THE NEXT PAGE. © 2023 College Board. Visit College Board on the web: collegeboard.org. 14 AP® Chemistry 2023 Free-Response Questions Begin your response to QUESTION 4 on this page. 4. A student is asked to prepare a buffer solution made with equimolar amounts of CH3 2 NH (aq) and CH3NH3Cl(s). The student uses 25.00 mL of 0.100 M CH3NH2(aq), which contains 0.00250 mol of CH3NH2, to make the buffer. (a) Calculate the mass of CH3NH3Cl(s) that contains 0.00250 mol of CH NH Cl 3 3 . The student has the following materials and equipment available. • Distilled water • 0.100 M CH3NH2(aq) • Solid CH NH Cl 3 3 • Electronic balance • Weighing paper • 50.00 mL buret • 50 mL beaker • 10.0 mL graduated cylinder • Small spatula • Pipets • pH meter (b) The following table contains a partial procedure for making the buffer solution. Fill in steps 1 and 4 to complete the procedure using only materials and equipment selected from the choices given. (Not all materials listed will be used. Assume that all appropriate safety measures are already in place.) Step Procedure 1 2 Place the solid in the 50 mL beaker. 3 Clean the buret and rinse with distilled water. 4 5 Use the buret to add 25.00 mL of 0.100 M CH NH ( 3 2 aq) to the beaker. 6 Mix well. 7 Check the pH with the pH meter. GO ON TO THE NEXT PAGE. © 2023 College Board. Visit College Board on the web: collegeboard.org. 15 AP® Chemistry 2023 Free-Response Questions Continue your response to QUESTION 4 on this page. The value of Kb for CH3NH2(aq) is 4.4 ¥ 10−4 , and the pH of the buffer the student prepared is 10.64. (c) The student prepares a second buffer solution. The student uses 25.00 mL of 0.050 M CH3NH2(aq) instead of 25.00 mL of 0.100 M CH3NH (aq) 2 , and half the mass of CH3NH3Cl(s) that was used in the first buffer. Is the pH of the second buffer greater than, less than, or equal to the pH of the first buffer? Justify your answer. Unauthorized copying or reuse of this page is illegal. Page 13 GO ON TO THE NEXT PAGE. © 2023 College Board. Visit College Board on the web: collegeboard.org. 16 AP® Chemistry 2023 Free-Response Questions Begin your response to QUESTION 5 on this page. 5. HCl is a molecular gas as a pure substance but acts as an acid in aqueous solution. (a) A sample of HCl(g) is stored in a rigid 6.00 L container at 7.45 atm and 296 K. (i) Calculate the number of moles of HCl(g) in the container. (ii) The rigid 6.00 L container of HCl(g) is cooled to a temperature of 271 K. Calculate the new pressure, in atm, of the HCl(g). (b) When HCl ionizes in aqueous solution, Cl−(aq) ions are formed. In the following box, draw three water molecules with proper orientation around the Cl− ion. Use to represent water molecules. GO ON TO THE NEXT PAGE. © 2023 College Board. Visit College Board on the web: collegeboard.org. 17 AP® Chemistry 2023 Free-Response Questions Continue your response to QUESTION 5 on this page. Acid (HA) Anion ( ) A− K Value a HNO2 − NO2 −4 5.6 ¥ 10 HCl − Cl 7 2.0 ¥ 10 HClO4 − ClO4 15 1.6 ¥ 10 The Ka values for three acids are shown in the preceding table. (c) The following particulate diagram represents the ionization of one of the acids in the data table. Water molecules have been omitted for clarity. Which acid (HNO2, HCl, or HClO4) is represented in the diagram? Justify your answer using the information in the table. GO ON TO THE NEXT PAGE. © 2023 College Board. Visit College Board on the web: collegeboard.org. 18 AP® Chemistry 2023 Free-Response Questions Begin your response to QUESTION 6 on this page. 6. Answer the following questions related to HBr(l) and HF(l). (a) In the following table, list all of the types of intermolecular forces present in pure samples of HBr(l) and HF(l). Liquid HBr(l) HF(l) Intermolecular forces present (b) The enthalpy of vaporization, ΔH vap, for each liquid is provided in the following table. Liquid HBr l)( HF( )l ΔH vap 17.3 kJ / mol 25.2 kJ / mol (i) Based on the types and relative strengths of intermolecular forces, explain why ΔH of HF(l) vap is greater than that of HBr(l). (ii) Calculate the amount of thermal energy, in kJ, required to vaporize 6.85 g of HF(l). GO ON TO THE NEXT PAGE. © 2023 College Board. Visit College Board on the web: collegeboard.org. 19 AP® Chemistry 2023 Free-Response Questions Continue your response to QUESTION 6 on this page. (c) Based on the arrangement of electrons in the Br and F atoms, explain why the bond length in an HBr molecule is greater than that in an HF molecule. GO ON TO THE NEXT PAGE. © 2023 College Board. Visit College Board on the web: collegeboard.org. 20 AP® Chemistry 2023 Free-Response Questions Begin your response to QUESTION 7 on this page. 7. Strontium hydroxide dissolves in water according to the following equation. The Ksp expression for strontium hydroxide is provided. 2+ 2+ − 2 Sr(OH) (s) Sr (aq) + 2 OH−(aq) K = [Sr ][OH ] 2 sp (a) A student draws the particulate diagram shown to represent the ions present in an aqueous solution of Sr(OH) 2. (Water molecules are intentionally omitted.) Identify the error in the student’s drawing. (b) The student prepares a saturated solution by adding excess Sr(OH) (s) 2 to distilled water and stirring until no more solid dissolves. The student then determines that [Sr2+ ] = 0.043 M in the solution. (i) Calculate the value of − [OH ] in the solution. (ii) Calculate the value of Ksp for Sr(OH) 2. GO ON TO THE NEXT PAGE. © 2023 College Board. Visit College Board on the web: collegeboard.org. 21 AP® Chemistry 2023 Free-Response Questions Continue your response to QUESTION 7 on this page. (c) The student prepares a second saturated solution of Sr( OH)2 in aqueous 0.10 M Sr(NO3) 2 instead of water. Will the value of − [OH ] in the second solution be greater than, less than, or equal to the value in the first solution? Justify your answer. (Assume constant temperature.) STOP END OF EXAM © 2023 College Board. Visit College Board on the web: collegeboard.org. 22