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FRQ Calculations with:Thermo, Electro, Kinetics

Stoich, Solutions, Gases, Labs, etc.

FRQ’s with :Bonding/IMAF’s

Atomic Structure, PeriodicityDescriptive (colors, precipitates)/Labs, etc.

6 Questions: (ALL are former Questions from the last 10 years of AP Exams)

Section IIFREE-RESPONSE QUESTIONS

AP Chemistry

Points Scored 6 Question Topics

___/ 10 = ______% 2. Electro, Stoich

___/ 09 = ______% 3. Descriptive, Stoich (limiting reactant)

___/ 09 = ______% 3. Stoich, Gases, Kinetics

___/ 08 = ______% 5. Lewis Str., Mol Geom., IMAFs, Redox, Thermo (∆S, ∆H)

___/ 09 = ______% 5. Descriptive (gas tests, pH solutions, precipitates)

___/ 08 = ______% 6. Elect. Configuration, Periodicity (Radius, IE), IMAFs

5 Fe2+(aq) + MnO4−(aq) + 8 H+(aq) → 5 Fe3+ (aq) + Mn2+(aq) + 4 H2O(l)

2. A galvanic cell and the balanced equation for the spontaneous cell reaction are shown above. The two reduction half-reactions for the overall reaction that occurs in the cell are shown in the table below.

(a) On the diagram, clearly label the cathode.

(b) Calculate the value of the standard potential, E°, for the spontaneous cell reaction.

(c) How many moles of electrons are transferred when 1.0 mol of MnO4–(aq) is consumed in the

overall cell reaction?

(d) Calculate the value of the equilibrium constant, Keq , for the cell reaction at 25°C. Explain what the magnitude of Keq tells you about the extent of the reaction.

Three solutions, one containing Fe2+(aq) , one containing MnO4–(aq) , and one containing H+(aq) ,

are mixed in a beaker and allowed to react. The initial concentrations of the species in the mixture are 0.60 M Fe2+(aq) , 0.10 M MnO4

–(aq) , and 1.0 M H+(aq) .

(e) When the reaction mixture has come to equilibrium, which species has the higher concentration, Mn2+(aq) or MnO4

–(aq) ? Explain.

(f) When the reaction mixture has come to equilibrium, what are the molar concentrations of Fe2+

(aq) and Fe3+(aq) ?

2010B AP® CHEMISTRY FREE RESPONSE QUESTIONS

Half-ReactionEo(V) at 298 K

Fe3+(aq) + e– Fe2+(aq) +0.77

MnO4−(aq) + 8 H+(aq) + 5 e– → Mn2+(aq) + 4 H2O(l) +1.49

2010B AP® CHEMISTRY FREE RESPONSE QUESTIONSANSWER SHEET

QUESTION 2 Your Score: ____ out of 10


QUESTION 2 (cont’d)

2008B AP® CHEMISTRY FREE RESPONSE QUESTIONS

8 H+(aq) + 4 Cl−(aq) + MnO4−(aq) 2 Cl2(g) + Mn3+(aq) + 4 H2O(l)

3. Cl2(g) can be generated in the laboratory by reacting potassium permanganate with an acidified solution of sodium chloride. The net-ionic equation for the reaction is given above.

(a) A 25.00 mL sample of 0.250 M NaCl reacts completely with excess KMnO4(aq) . The Cl2(g) produced is dried and stored in a sealed container. At 22°C the pressure of the Cl2(g) in the container is 0.950 atm.

(i) Calculate the number of moles of Cl−(aq) present before any reaction occurs.

(ii) Calculate the volume, in L, of the Cl2(g) in the sealed container.

An initial-rate study was performed on the reaction system. Data for the experiment are given in the table below.

Trial [Cl–] [MnO4–] [H+] Rate of Disappearance of MnO4– in M s–1

1 0.0104 0.00400 3.00 2.25 x 10–8

2 0.0312 0.00400 3.00 2.03 x 10–7

3 0.0312 0.00200 3.00 1.02 x 10–7

(b) Using the information in the table, determine the order of the reaction with respect to each of the following. Justify your answers.

(i) Cl−

(ii) MnO4−

(c) The reaction is known to be third order with respect to H+ . Using this information and your answers to part (b) above, complete both of the following:

(i) Write the rate law for the reaction.

(ii) Calculate the value of the rate constant, k, for the reaction, including appropriate units.

(d) Is it likely that the reaction occurs in a single elementary step? Justify your answer.

2010 AP® CHEMISTRY FREE RESPONSE QUESTIONS

2010 AP® CHEMISTRY FREE RESPONSE QUESTIONSANSWER SHEET


5. Hydrazine is an inorganic compound with the formula N2H4 .

(a) In the box below, complete the Lewis electron-dot diagram for the N2H4 molecule by drawing in all the electron pairs.

(b) On the basis of the diagram you completed in part (a), do all six atoms in the N2H4 molecule lie in the same plane? Explain.

(c) The normal boiling point of N2H4 is 114°C, whereas the normal boiling point of C2H6 is −89°C. Explain, in terms of the intermolecular forces present in each liquid, why the boiling point of N2H4 is so much higher than that of C2H6 .

(d) Write a balanced chemical equation for the reaction between N2H4 and H2O that explains why a solution of hydrazine in water has a pH greater than 7.

N2H4 reacts in air according to the equation below.

N2H4(l) + O2(g) → N2(g) + 2 H2O(g) ΔH° = −534 kJ mol−1

(e) Is the reaction an oxidation-reduction, acid-base, or decomposition reaction? Justify your answer.

(f) Predict the sign of the entropy change, ΔS, for the reaction. Justify your prediction.

(g) Indicate whether the statement written in the box below is true or false. Justify your answer.


The large negative ΔH° for the combustion of hydrazine results from the large release of energy that occurs when the strong bonds of the reactants are broken.

SiO2 CO2

6. Answer the following questions related to sulfur and one of its compounds.

(a) Consider the two chemical species S and S2– .

(i) Write the electron configuration (e.g., 1s2 2s2 . . .) of each species.

(ii) Explain why the radius of the S2− ion is larger than the radius of the S atom.

(iii) Which of the two species would be attracted into a magnetic field? Explain.

(b) The S2− ion is isoelectronic with the Ar atom. From which species, S2− or Ar , is it easier to remove an electron? Explain.

(c) In the H2S molecule, the H–S–H bond angle is close to 90°. On the basis of this information, which atomic orbitals of the S atom are involved in bonding with the H atoms?

(d) Two types of intermolecular forces present in liquid H2S are London (dispersion) forces and dipole-dipole forces.

(i) Compare the strength of the London (dispersion) forces in liquid H2S to the strength of the London (dispersion) forces in liquid H2O . Explain.

(ii) Compare the strength of the dipole-dipole forces in liquid H2S to the strength of the dipole-dipole forces in liquid H2O . Explain.


Answer KEY

2. 2010B #2 Electro, Stoich

3. 2008B #3 Descriptive (precipitate), Stoich (limiting reactant)

3. 2010 #3 Stoich, Gases, Kinetics

5. 2011 #5 Lewis Str., Mol Geom., IMAFs, Redox, Thermo (S, ∆H)

5. 2005 #5 Descriptive (gas tests, pH solutions, precipitates)

6. 2009 #6 Elect. Configuration, Periodicity (Radius, IE), IMAFs

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