2013 frq.pdf - 2013 AP\u00ae CHEMISTRY FREE-RESPONSE QUESTIONS 2 Answer the following questions involving the stoichiometry and thermodynamics of reactions

2013 frq.pdf - 2013 AP® CHEMISTRY FREE-RESPONSE QUESTIONS...

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2013 AP ® CHEMISTRY FREE-RESPONSE QUESTIONS © 2013 The College Board. Visit the College Board on the Web: . GO ON TO THE NEXT PAGE. -7- 2. Answer the following questions involving the stoichiometry and thermodynamics of reactions containing aluminum species. 2 Al 2 O 3 ( l ) + 3 C( s ) ¡ 4 Al( l ) + 3 CO 2 ( g ) An electrolytic cell produces 235 g of Al( l ) according to the equation above. (a) Calculate the number of moles of electrons that must be transferred in the cell to produce the 235 g of Al( l ). (b) A steady current of 152 amp was used during the process. Determine the amount of time, in seconds, that was needed to produce the Al( l ). (c) Calculate the volume of CO 2 ( g ), measured at 301 K and 0.952 atm, that is produced in the process. (d) For the electrolytic cell to operate, the Al 2 O 3 must be in the liquid state rather than in the solid state. Explain. When Al( s ) is placed in a concentrated solution of KOH at 25°C, the reaction represented below occurs. 2 Al( s ) + 2 OH 0 ( aq ) + 6 H 2 O( l ) ¡ 2[Al(OH) 4 ] 0 ( aq ) + 3 H 2 ( g ) Half-reaction E ° (V) [Al(OH) 4 ] 0 ( aq ) + 3 e 0 ¡ Al( s ) + 4 OH 0 ( aq ) 0 2.35 2 H 2 O( l ) + 2 e 0 ¡ H 2 ( g ) + 2 OH 0 ( aq ) 0 0.83 (e) Using the table of standard reduction potentials shown above, calculate the following. (i) E °, in volts, for the formation of [Al(OH) 4 ] 0 ( aq ) and H 2 ( g ) at 25°C (ii) D G °, in kJ/mol rxn , for the formation of [Al(OH) 4 ] 0 ( aq ) and H 2 ( g ) at 25 q C
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AP ® CHEMISTRY 2013 SCORING GUIDELINES © 2013 The College Board. Visit the College Board on the Web: . Question 2 Answer the following questions involving the stoichiometry and thermodynamics of reactions containing aluminum species. 2 Al 2 O 3 ( l ) + 3 C( s ) 4 Al( l ) + 3 CO 2 ( g ) An electrolytic cell produces 235 g of Al( l ) according to the equation above. (a) Calculate the number of moles of electrons that must be transferred in the cell to produce the 235 g of Al( l ). 1 mol Al 235 g Al = 8.71 mol Al 26.98 g Al Al 3+ + 3 e Al , therefore, 3 mol e transferred per mol Al 3 mol 8.71 mol Al 26.1 mol 1 mol Al e e 1 point is earned for the number of moles of Al. 1 point is earned for correct stoichiometry and the number of moles of electrons.
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