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Practice Test 10 - AP Chemistry

20 questions. Answer them in any order, then submit to see your score and every explanation.

  1. The noble gases He, Ne, and Ar are in Group 18. Which element has the lowest first ionization energy?
  2. A solution of a colored compound is measured at 400 nm. In a 1.00 cm cuvette, A=0.10A=0.10 for a solution with c=2.0×10−5 Mc=2.0\times10^{-5}\ \text{M}. What is ε\varepsilon at 400 nm?
  3. A 500. mL solution of 0.10 M acetic acid, CH3COOHCH_3COOH, is prepared. Given that the acid-dissociation constant, KaK_a, for acetic acid is 1.8×10−51.8 \times 10^{-5}, what is the approximate number of moles of H+H^+ ions at equilibrium?
  4. Element P has atomic number 9. What is the most likely charge of the monatomic ion formed by P?
  5. A reaction-energy diagram shows two peaks with a deep valley (intermediate) between them. Which statement is correct about identifying the rate-determining step? (Vertical axis: potential energy; horizontal axis: reaction coordinate.)
  6. In the cyanate ion, OCN−^-, consider these resonance structures: (1) − ⁣^-\!O–C≡N, (2) O=C=N−^-, and (3) O≡C–N−^-. Which resonance structure is expected to be the most stable contributor?​
  7. The formation of an ionic bond between a metal atom and a nonmetal atom is primarily driven by the
  8. A student examines the reaction between aqueous sodium thiosulfate and aqueous hydrochloric acid, which produces sulfur as a precipitate (mechanism assumed unchanged between trials). Trial 1 uses a more concentrated Na2S2O3(aq)\text{Na}_2\text{S}_2\text{O}_3(aq) solution; Trial 2 uses a more dilute Na2S2O3(aq)\text{Na}_2\text{S}_2\text{O}_3(aq) solution. The HCl concentration, temperature, and total volume are the same in both trials. The precipitate forms faster in Trial 1. Which statement best explains the faster rate based on collisions?
  9. A student dissolves a small amount of ethanol, CH3CH2OH(l)\text{CH}_3\text{CH}_2\text{OH}(l), in water. Which particulate-level description best represents how ethanol is dispersed and interacts with water?
  10. A cell is assembled with two half-cells and a salt bridge. When the external circuit is completed, electrons flow through the wire without any external power supply, and the system can be used to charge a phone briefly. Which statement best describes the cell and the reaction driving electron flow?
  11. A reaction mixture is at equilibrium for CO2(g)+H2(g)⇌CO(g)+H2O(g)\text{CO}_2(g)+\text{H}_2(g)\rightleftharpoons \text{CO}(g)+\text{H}_2\text{O}(g). The equilibrium concentrations are [CO2]=0.25 M[\text{CO}_2]=0.25\,\text{M}, [H2]=0.50 M[\text{H}_2]=0.50\,\text{M}, [CO]=0.10 M[\text{CO}]=0.10\,\text{M}, and [H2O]=0.20 M[\text{H}_2\text{O}]=0.20\,\text{M}. What is the value of KcK_c?
  12. Element F has a mass spectrum with peaks at m/z=40m/z=40 (96) and m/z=42m/z=42 (4). Assuming singly charged ions, what is the average atomic mass of F?
  13. At a given temperature, the equilibrium constant for the reaction PCl5(g)⇌PCl3(g)+Cl2(g)\mathrm{PCl_5(g) \rightleftharpoons PCl_3(g) + Cl_2(g)} is KK. What is the relationship between KnewK_{\text{new}} and KK for the reaction 2PCl5(g)⇌2PCl3(g)+2Cl2(g)\mathrm{2PCl_5(g) \rightleftharpoons 2PCl_3(g) + 2Cl_2(g)}?
  14. Use the average bond enthalpies given to estimate ΔH\Delta H for the reaction: H2(g)+Br2(g)→2HBr(g)\mathrm{H_2(g) + Br_2(g) \rightarrow 2HBr(g)}. Bond enthalpies: H−H=436 kJ/mol\mathrm{H-H}=436\ \text{kJ/mol}, Br−Br=193 kJ/mol\mathrm{Br-Br}=193\ \text{kJ/mol}, H−Br=366 kJ/mol\mathrm{H-Br}=366\ \text{kJ/mol}. What is the estimated enthalpy change, ΔH\Delta H, for the reaction?
  15. A student is balancing the equation Fe+O2→Fe2O3\mathrm{Fe + O_2 \rightarrow Fe_2O_3}. Which statement reflects the key conservation principle used to balance any chemical equation?
  16. A sealed container initially holds 2.0 mol\mathrm{2.0\,mol} of O2(g)\mathrm{O_2(g)} and 1.0 mol\mathrm{1.0\,mol} of N2(g)\mathrm{N_2(g)} thoroughly mixed at constant temperature. The gases are then separated into two equal-volume compartments by inserting an impermeable partition so that one side contains only O2(g)\mathrm{O_2(g)} and the other side contains only N2(g)\mathrm{N_2(g)}. What is the sign of ΔS\Delta S for the system?
  17. Two bases are compared: I: NH3 II: NF3 Which best explains why NH3 is a stronger BrnstedLowry base than NF3?
  18. A student tries to dissolve calcium carbonate, CaCO3(s), in water, H2O(l), at room temperature. CaCO3 is an ionic solid with relatively strong lattice energy; water is polar and can form ion–dipole interactions. Is CaCO3 likely to be very soluble in pure water, and why?
  19. At 1 atm, liquid nitrogen, N2_2(l), warms and boils to form N2_2(g) in an open container. Considering the nitrogen as the system during boiling (liquid to gas), does entropy increase, decrease, or remain approximately constant?
  20. Which of the following properties of aluminum is primarily explained by the delocalized nature of its valence electrons?

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