2023 AP Chemistry Free-Response Questions
Advanced PlacementAP ChemistryFree ResponseScience
7 questions46 pts
7 gradable46 rubric criteria0 dependencies
q1Question 1
q1
Question 1
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, MnₓClᵧ(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. x Mn(s) + y HCl(aq) → MnₓClᵧ(aq) + y/2 H₂(g) The student heats the resulting mixture until only MnₓClᵧ(s) remains in the beaker. The data are given in the following table. | Measurement | Mass | |---|---| | Mass of empty beaker | 60.169 g | | Mass of beaker and Mn(s) | 61.262 g | | Mass of beaker and MnₓClᵧ after heating to constant mass | 62.673 g | (b) Calculate the mass of Cl in the sample of MnₓClᵧ(s) remaining in the beaker. (c) Calculate the number of moles of Cl in the sample of MnₓClᵧ(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 MnₓClᵧ(s). (e) The student repeats the experiment using the same amounts of Mn and HCl and notices that some of the MnₓClᵧ 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. (f) Another compound of manganese, MnO₂, is used in alkaline batteries, represented by the following diagram. Some half-reactions are given in the table. Diagram labels: Graphite Rod; MnO₂ Paste; KOH Paste; Zinc Case. | Reduction Half-Reaction | E° (V) | |---|---:| | Zn²⁺(aq) + 2 e⁻ → Zn(s) | −0.76 | | ZnO(s) + H₂O(l) + 2 e⁻ → Zn(s) + 2 OH⁻(aq) | −1.28 | | 2 MnO₂(s) + H₂O(l) + 2 e⁻ → Mn₂O₃(s) + 2 OH⁻(aq) | 0.15 | (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 E°cell 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.
Rubric Criteria (10)
C1The response gives the complete ground-state electron configuration of a manganese atom as 1s2 2s2 2p6 3s2 3p6 4s2 3d5 or [Ar]4s2 3d5.
1.0000pts
C2The response identifies the 4s subshell as the subshell from which electrons are lost when manganese forms cations, consistent with the electron configuration in part (a)(i).
1.0000pts
C3The response calculates the mass of chlorine in the dry solid as 1.411 g Cl, using the stated experimental values.
1.0000pts
C4The response converts 1.411 g Cl to 0.03980 mol Cl, consistent with the mass calculated in part (b).
1.0000pts
C5The response uses 0.03980 mol Cl and 0.0199 mol Mn to obtain a 2:1 mol ratio of Cl to Mn and identifies the empirical formula as MnCl2.
1.0000pts
C6The response states that the calculated chlorine amount would be less than the actual amount and explains that splattering would reduce the final mass of the dry beaker and MnxCly, thereby reducing the calculated mass and moles of chlorine in the dry solid.
1.0000pts
C7The response gives the balanced overall equation 2 MnO2(s) + Zn(s) → Mn2O3(s) + ZnO(s).
1.0000pts
C8The response calculates E°cell as 1.43 V using 0.15 V − (−1.28 V), consistent with the balanced equation in part (f)(i).
1.0000pts
C9The response calculates ΔG° as −276 kJ/molrxn using ΔG° = −nFE° with n = 2 mol e− per mol reaction and E°cell = 1.43 V, consistent with part (f)(ii).
1.0000pts
C10The response disagrees that the battery's mass changes and justifies this by stating that the battery is enclosed or sealed and that all reactants and products are solid, so no gases enter or exit.
1.0000pts
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